Activation and Metacognition of Inaccessible Stored ...

Jotltnal of Expo'imental Psychology: Learning, Memory, and ~ i t i o n 1987, Vol. 13, No. 2, 187-205

Copyright 1987 by the American Psychological Assooation, Inc. 0278-7393/87/$120.75

Activation and Metacognition of Inaccessible Stored Information: Potential Bases for Incubation Effects in Problem Solving Ilan Yaniv and David E. Meyer University of Michigan Two experiments were conducted with a hybrid procedure that involved a battery of indirect criterion tests designed to study the activation and metacognition of inaccessible stored information. In each experiment, subjects first attempted to recall some rare target words in response to a series of deflnitions meant to tue retrieval from long.term semantic memory. For the words that could not be recalled initially, the subjects rated their feelings of knowing. They then performed a lexicaldecision task in which the target words and other control words were presented. Reaction times were measured as a function of the feeling-of-knowing ratings and the length of the interval between the initial exposure to the definitions and the subsequent lexical decisions. Faster decisions occurred for the target words than for the controls, especially when strong feelings of knowing had been expressed about the tarsets. Similar facilitation was obtained in a subsequent old-new recognition task. It appears that unsuccessful attempts to retrieve inaccessible stored information prime the later recognition of the information through a process of spreading activation. Such activation may sensitize people to future occurrences of stimulus inputs needed for insightful solutions of semantically rich problems.

People often seem to have retained bits of information that, at rimes, cannot be retrieved from long-term memory. For example, in a discourse on retrieval failures, William James ( 1890/1950, p. 251) wrote that there is "a gap that is intensely active" in the memory of a person who is trying to recall a forgotten name; when wrong names corne to mind, the gap acts to reject them as if they do not fit a requisite mold. Two striking phenomena may accompany such memory gaps. First, individuals who experience a gap sometimes think that they can report how weU they know the desired information, despite being unable to recall it at the moment. Second, after a retrieval failure, the associated gap may remain active for an extended period of rime. It is not uncommon that an unrecalled naine will enter consciousness unexpectedly during subsequent unrelated activities (cf. Norman & Bobrow, 1976). In certain respects, this surprise recall resembles flashes ofinsight during ditticult problem solving (Koestler, 1964; Wallas, 1926). The present article describes some o f o u r research on feelings of knowing and memory performance following subjects' unsuccessful attempts at retrieval. We begin by reviewing past literature on feelings of knowing and their potential relation to

incubation effects in problem solving. Next, we outline a hybrid procedure that combines a rare-word definition task, a lexicaldecision task, and an old-new recognition task to investigate the activation of inaccessible stored information. We then report two representative experiments with this procedure. The results of the experiments demonstrate that unsuccessful retrieval attempts prime subjects for later recognition of unrecalled items, and that the degree of priming is positively correlated with feelings of knowing elicited at the rime of the initial retrieval failure. A process of spreading activation in long-term semantic memory may mediate the priming effect and pave the way to eventual accurate recall. It is also conceivable that this activation process provides a partial basis for incubation effects and insight in problem solving.

Feelings o f K n o w i n g Intuitively, feelings of knowing constitute a form of metacognition (Wellman, 1977). Being unable to produce some requested information, an individual may instead supply a subjective judgment about the underlying status of that information in his or her long-terre memory. Such performance is particularly interesting in light of current cognitive theories, which hypothesize that forgetting results not from permanent loss of information but from temporary inaccessibility (Crowder, 1976, chap. l; Tulving & Pearlstone, 1966). According to these theories, contextual cues play an important role in recall, and they significantly modulate the retrieval of stored information. A retrieval failure that induces a confident feeling of knowing could then be due to the presence of partially but not completely adequate cues to recall, and future encounters with more adequate cues could yield successful retrieval despite the prior failure.

Portions ofthis research were first presented at a meeting ofthe Midwestern Psychological Association, Chieago, IUinois (Yaniv & Meyer, 1985). Partial support was provided by National Institute of Mental Health Grant R01-MH3884 to The University of Michigan, David E. Meyer, Principal Investigator. We thank Janet Metcalfe, Thomas Nelson, Henry L. Roediger III, and Daniel Schacter for helpful comments on an earlier version ofthe paper. We also thank Nancy Lisch for technical assistance. Correspondence concerning this article should be addressed to David E. Meyer, Human Performance Center, Department of Psychology,University of Michigan, 330 Paekard Road, Ann Arbor, Michigan 48104. 187

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The PrototypicalParadigm Because of the preceding considerations, some experimental research has explored the extent to which feelings of knowing are indeed accurate. Feeling-of-knowing studies have relied on a prototypical paradigm with three phases: an initial question period, subsequent feeling-of-knowing judgments, and a final criterion test. During the initial question period, a subject is asked to recall the answers to difl9 general-information questions. This yields a subset of questions for which the subject cannot currently provide the correct answers. Next, the subject makes feeling-of-knowing judgments about every item in that subset. Finally, to assess the accuracy ofthe judgments, the subject is given the criterion test, whose positive outcome does hOt require successful retrieval per se, but does require the previously unrecalled information to be stored in memory and to be evidenced in some salient way. The criterion test may involve multiple-choice recognition (Freedman & l_andauer, 1966; Hart, 1965, 1967; Read & Brute, 1982; Schacter, 1983), cued recaU (Gruneberg & Monks, 1974), reminiscence (Read & Bruce, 1982), perceptual identification (Nelson, Gerler, & Narens, 1984), or relearning (Nelson et al., 1984). A general conclusion from this research is that feelings of knowing are far from perfect. When such feelings are strong, however, they do tend to predict above-chance performance on the final criterion test, and they may reflect the amount of partially activated information in memory after an initial confrontation with a ditt9 retrieval task. For example, Brown and McNeill (1966) precipitated "tip-of-the-tongue" experiences by presenting definitions of low-frequency English words to subjects and asking them to recall the designated words from longterre memory. Subjects who failed to recall the words but who had tip-of-the-tongue experiences could report the initial letters and the numbers of syllables in the words at a level greater than chance. Similar results have been reported by other investigators as well (e.g., Koriat & Lieblich, 1974, 1977). People's ability to have accurate feelings of knowing seems especially useful given that human memory, unlike artificial memory systems, is sometimes capricious. With a computer memory, for example, a failure to retrieve some desired information ordinarily implies that the information does not exist in memory. However, with human memory, such failures do not necessarily imply the complete absence of sought for information, soit is adaptive for a person to have ancillary indicators that signal when inaccessible stored information may become available later. Strong feelings of knowing could indicate significant activation of memory traces related to an apparently missing target item. In turn, this activation might influence the course of future performance atter unsuccessful retrieval attempts, perhaps facilitating the assimilation of relevant information encountered subsequently.

Mechanismsfor Feelingsof Knowing To explain exactly how accurate feelings of knowing might be achieved, two alternative classes of mechanisms have been proposed. Nelson et al. (1984) referred to these as "trace-access mechanisms" and "inferential mechanisms." Although the various alternatives share certain commonalities, they emphasize

different potential bases on which feelings of knowing mig,ht rest. With the trace-access mechanisms, a person is assumed to have partial access to a memory trace of an unrecalled target item, and some aspect ofthis trace directly mediates feeling-ofknowing judgments about the item. The relevant aspects for accurate judgments could include the level of subthreshold trace strength, residual semantic or physical features contained in the trace, and so forth (Nelson et al., 1984). By contrast, the inferential mechanisms assume that feelings of knowing do not enrail access to a residual trace ofthe targeted item itself. Instead, other relevant facts supposedly are monitored by a subject to predict indirectly the likelihood of correct criterion-test performance. Some useful sources of such facts would include related episodic information stored in long-term memory, familiarity with the initial probe question posed to cue the recall of the target item, and tbe subject's assessment of lais or ber general expertise regarding the topic area in question (Nelson et al., 1984). At present, it is still not clear to what extent each of these various types of mechanisms contributes to feelings of knowing. However, a plausible scenario would be that they somehow operate combinatorially. Perhaps the output of one mechanism provides inputs to others, and vice versa, as proposed in interactive-activation models of information processing (e.g., McClelland & Rumelhart, 1981). As will be outlined later, our studies bear on this d a i m by testing when and how the memory trace ofa currently inaccessible item may be at least partially primed for a period oftime after information is processed from an initial probe question concerning the item. I n c u b a t i o n Effects in P r o b l e m Solving Besides their import for theories of memory performance, feeling-of-knowing studies also have some potential bearing on the source of incubation effects in problem solving (cf. Metcalfe, 1986). By definition, the term incubationrefers to an increased likelihood of successfully solving a ditticult problem as a result of placing a delay between an initial period of intense work on the problem and another subsequent period of conscious effort toward completing the problem's solution (Posner, 1973, chap. 7, p. 171). Such an increase has been documented in several experiments (e.g., Fulgosi & Guilford, 1968; Murray & Denny, 1969; Silveira, 1971, cited in Posner, 1973, chap. 7, p. 172). The circumstances surrounding apparent occurrences of incubation seem at least somewhat similar to those associated with research on feelings of knowing. In particular, scientists, artists, and other creative individuals have reported anecdotally that reaching the solution to a difl~cult problem often involves four successive phases, including (a) intense but unsuccessful confrontation with the problem, (b) a decision to put the problem aside, (c) a dormant period with no further conscious work on the problem, and (d) a flash of insight in which the solution suddenly enters consciousness while the individual is dreaming or engaged in idle thought (Koestler, 1964; Patrick, 1937; Wallas, 1926). The following well-known quote from the mathematician Poincar› illustrates this sequence ofevents: For fiffeen days I strove to prove that there could not be any functions like those I have since called Fuchsian functions. I was then very ignorant; every day I seated myself at my work table,

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ACTIVATION AND METACOGNITION stayed there an hour or two, tried a great number of combinations and reached no results. One evening, contrary to my usual custom, I drank black coffee and could hOt sleep. Ideas rose in crowds; I felt them collide until pairs interlocked, so to speak, making a stable combination. By the next morning I had established the existence of a class of Fuchsian functions, those which corne from the hypergeometric series; I had only to write out the results, which took but a few hours. (Poincare, 1952, pp. 36-37)

Here we see certain aspects of the situation that closely resemble those present when feelings of knowing arise. The similarities include an initial unsuccessful attempt to produce a satisfactory output (i.e., solution/answer) in response to a ditt9 stimulus input (i.e., problem/question), foUowed by a subsequent coalescence of mental elements that together resolve the initial difficulty. Like trying to answer questions about relatively unfamiliar facts, the creative solution to a problem may involve retrieving and integrating diverse bits of information through remote associations in long-term memory (Glucksberg & Weisberg, 1966; Judson, Cofer, & Gelfand, 1956; Penney & Winsor, 1982; Weisberg & Alba, 198 l). To the extent that the relevant information is stored but currently inaccessible, the problem solution would then be precluded for a period of time in the saine manner as when item recall fails during feeling-ofknowing studies. An initial failure could occur, for example, because the stimulus confguration at the start of processing provides inadequate retrieval cues and/or because components ofthe memory traces are too weak for present purposes. Of course, we do hOt mean to imply that the tasks faced by subjects in the typical feeling-of-knowing paradigm and creative problem solving are exact equivalents. To answer a ditficuit factual question or generate feelings ofknowing about it, a subject could rely entirely on prestored information. This is hOt the case for diflicult problems, which, by definition, require new knowledge structures and novel combinations of ideas to be generated. Nevertheless, prestored bits of information, which may be inaccessible at the outset, could still presumably play an integral role as part of most problem solutions. It is hard to imagine situations in which the solution to a problem emerges without any contributions from past experience. It is easy to imagine how the various types of mechanisms proposed to account for accurate feelings of knowing (Nelson et al., 1984) might contribute to incubation effects in problem solving. If both the partial access of key items' memory traces and the progression of inferences through other relevant stored information generate some spreading activation, then subsequent enhanced memory performance ultimately could yield successful solutions. As previous cognitive theorists have noted, the "dormant period" between consecutive confrontations with a problem offers opportunities for an individual to experience new environmental stimulus inputs, which may trigger chains of associations and suggest analogies toward a good solution (Gick & Holyoak, 1980; Judson et al., 1956; Penney & Winsor, 1982; Posner, 1973, chap. 7; Read & Bruce, 1982). When the individual has appropriate memory traces activated from past solution failures (i.e., a "prepared mind"; Pasteur, cited in Posner, 1973, chap. 7, p. 148), the assimilation of these new stimuli presumably would occur more efl]ciently and with higher probability. Consequently, by investigating where, when, what, and how the activation of inaccessible stored information

takes place, we may gain footholds on some ofthe bases underlying incubation effects. Overview o f Experiments The experiments reported in this article deal specifically with a number of related questions about memory performance that involves inaccessible stored information. Can the future recognition ofcurrently unrecaUable items be primed by past unsuccessful retrieval attempts? Is it possible for a priming effect to occur without explicit reference to the original probe stimulus that elicited the retrieval failure? To what extent do feelings of knowing provide accurate predictors of this priming? Might spreading activation in long-terre memory, which has been studied as part of research on semantic information processing (e.g., Meyer & Schvaneveldt, 1971, 1976; Meyer, Schvaneveldt, & Ruddy, 1972, 1975), mediate the magnitude of observed priming and reported feelings? Is the processing of episodic as weU as semantic information influenced by the activation? Given our results, it will not be possible to answer ail of these questions definitively, but we may take further steps toward resolving them. H y b r i d Procedure

We used a hybrid procedure with several phases. The phases included a rare-word definition task (Brown & McNeill, 1966), feeling-of-knowing judgments (Hart, 1965), a lexical-decision task (Meyer & Schvaneveldt, 1971), and an old-new recognition task. On each trial of the first phase, a definition of some relatively rare English target word was presented to a subject. The subject tried to recall the target word designated by the definition, and then typed the outcome, if any, on a computer keyboard. The definition task induced the subject t o b e in one ofthree possible memory states. These consisted of(a) a correctrecall state reached when the target word was successfully retrieved from memory, (b) an incorrect-recall state reached when some word other than the target was retrieved, and (c) a norecall state reached when no word was retrieved. If the subject could hOt produce any word, then he or she judged how strong the feeling of knowing was, despite being unable to retrieve the target word at the moment. The next phase of the procedure implemented the lexicaldecision task, in which the subject had to classify various strings of letters as English words or nonwords. For each letter string presented, a positive or negative decision was made, and reaction time was measured as a function of how the test stimuli were related to the initial definitions and to the different subjective memory states induced by these definitions. Our test stimuli consisted of the relevant target words that would have qualified as appropriate responses to the definitions, other control words that were irrelevant to them, and nonwords. The final phase ofthe procedure was a speeded old-new recognition task, in which subjects were presented with ail of the old words used in the prior lexical-decision task, including both the ones relevant to the initial definitions (targets) and the irrelevant ones (controls). There were also new distractor words hOt shown before. Subjects had to give positive judgments for the old words and negative judgments for the new distractors.

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Again, we measured reaction time and accuracy as a function of the subjects' memory states and the relation between the test stimuli and the definitions.

Rationale On the basis of a preliminary normative study described later, we anticipated that the rare-word definition task would induce retrieval failures even among subjects who had some knowledge of the designated target words. The subsequent lexical-decision and old-new recognition tasks tested the strength of residual semantic and episodic memory traces for the target words following unsuccessful attempts to retrieve them. This allowed us to assess some basic hypotheses about feelings of knowing and the activation of inaccessible stored information. As part ofthe assessment, the control words that were irrelevant to the presented definitions helped establish useful performance benchmarks. Lexical-decision task. We used the lexical-decision task because previous research has documented its ability to reveal the effects of factors, such as semantic and repetition priming, that influence the accessibility of information in long-term memory. Meyer and Schvaneveldt (1971) showed that reaction times to make lexical decisions about pairs of words are shorter if the words have close semantic relations. Similarly, Scarborough, Cortese, and Scarborough (1977) showed that repeating a word in a lexical-decision task reduces the latency of responses to that word. To explain such data, a number of theorists have proposed that lexical decisions depend on the presence of spreading activation in long-terre memory and on variations in the resting activation levels of semantic-network nodes (e.g., Collins & Loftus, 1975; McClelland & Rumelhart, 1981; Meyer & Schvaneveldt, 1971, 1976; Morton, 1969). Assuming the merit of these proposais, the lexical-decision task may provide a way of tapping into mechanisms that underlie feelings of knowing and priming of stored but temporarily inaccessible information. At the saine time, some important differences should be noted between our use ofthe lexical-decision task and most earlier applications of it. The stimuli selected for experiments on semantic priming have typically consisted of words with relatively high familiarity and strong associations (e.g., bread-butter, nurse-doctor, etc.; Meyer & Schvaneveldt, 1971, 1976; cf. Fischler, 1977, 1981). Also, the time interval between the presentation of an initial context (i.e., priming word or sentence) and subsequent test item (i.e., word or nonword) has typically been quite brief (viz., a few seconds or less). Combining brief interstimulus intervals with strong word associations maximizes the prospects of obtaining large facilitation effects. On the other hand, the present research used materials with considerably longer intervals and weaker associations. Conceivably, this could eliminate most, if not ail, of the apparent priming. Indeed, Meyer et al. (1972) found that semantic facilitation effects may be reduced on the order of 50% or more merely by inserting a single unrelated word or an unfilled interval of 4 s between two closely related words. It is n o t a foregone conclusion that significant priming would occur in the experiments reported here. Our approach also differs in some ways from previous re-

search on feelings of knowing. An important aspect of the difference involves a distinction that we draw between "direct" and "indirect" criterion tests. As described earlier, the prototypical feeling-of-knowing paradigm incorporates three phases: initial question period, feeling-of-knowingjudgments, and final criterion test. In many past studies, the criterion tests used to assess subjects' feelings of knowing have been "direct" ones, specifically referring to the probe questions that evoked those feelings. For example, one such test required subjects to make a multiple-choice selection among a set of alternative items displayed along with some previously unanswered question (Freedman & Landauer, 1966; Hart, 1965, 1967; Metcalfe, 1986; Read & Bruce, 1982; Schacter, 1983). The subjects were supposed to evaluate the items as correct answers with respect to the question, choosing the best item from the set. This tends to limit the informativeness of the test. The amount of effort expended in attempting to make an accurate choice could be influenced by prior feelings of knowing about the question at hand, creating a potential confound between metacognition and capacity allocation; that is, a person may try harder to select the correct answer after he or she has given a confident feelingof-knowing judgment (cf. Gruneberg, Monks, & Sykes, 1977). A similar concern applies to other direct criterion tests (e.g., cued recall; Gruneberg & Monks, 1974). By contrast, the present criterion test involving the lexical-decision task is an "indirect" one that helps overcome such concerns. It does not require subjects to make their decisions about the target words with respect to prior probe questions (i.e., rare-word definitions). The necessary lexical decisions are logically independent of the initial question period; they could be reached even ifthere were no exposure to the questions and no evoked feelings of knowing. Moreover, the subjects' lexical-decision performance on the target words may be compared with their performance on the control words, further alleviating concerns over troublesome confounds. There has been one feeling-of-knowing study with a criterion test similar in some respects to the lexical-decision task. After an initial question period and judgment about feeling ofknowing, Nelson et al. (1984) had subjects attempt to identify a target word displayed tachistoscopically. The probability of correct identification was measured as a function of the word's exposure duration. In principle, performance of the identification task, like performance of the lexical-decision task, could have proceeded without any explicit reference to the prior question period or feelings of knowing elicited by it. However, in Nelson et al.'s (1984) application, subjects were specifically instructed to view the displayed target as being "the answer" to the prior question, and the question itselfwas visible during the criterion test. This compromises Nelson et al?s finding that higher identification probabilities occurred for the target word when the associated question induced strong as opposed to weak feelings of knowing. The higher probabilities may have resulted from ancillary response biases and "off-line" processing ofthe target word after its brief exposure. It seems likely that the lexicaldecision task would provide a more sensitive indicator of unbiased "on-line" processing (Fischler, 1981), and that by temporally separating the target-word exposures from the initial questions, as we do here, a better assessment of residual memory-trace strength could emerge.

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Old-new recognition task. Another sensitive indicator is provided by the old-new recognition task. As described earlier (Hybrid Procedure), the "old" items for the recognition task included both the target words and the control words presented during the prior lexical-decision task. This let us assess whether the assimilation of episodic information about previously inaccessible stored items depends on the extent to which memory traces of them already have been activated by unsuccessful retrieval attempts. In particular, the rare-word definitions initially served to prime the traces of the targets but hOt the controis, so that when the subjects later performed the lexical-decision task, there was a potentially better basis for encoding the explicit encounters that the lexical-decision task entailed with the targets. We reasoned that if residual trace activation facilitates the encoding process, and if apparent answers to problematic questions attract attention because of the facilitation, then retrospective judgments about the targets should benefit correspondingly at the time of the old-new recognition task. If, on the other hand, residual trace activation does not promote the uptake of relevant episodic information, then "old" judgments about the controls might equal those about the targets. Like the lexical-decision task, the old-new recognition task is an indirect criterion test requiring no explicit reference to the original probe questions or to the feelings ofknowing induced by them. Construction of Definition Norms Before our main experiments, we conducted a preliminary normative study. The objective of this study was to construct a set of rare low-frequency words that exist in the passive vocabularies of most college students and to generate appropriate definitions for these words. Selected definitions were then used in the initial phases of the main experiments for inducing retrieval failures and subjective feelings of knowing. The corresponding low-frequency words were used as target and control items in the subsequent lexical-decision and old-new recognition tasks. A total of 240 potential word definitions were taken from Webster's Collegiate Dictiona~ and several other definitions were adapted from the materials of Brown and McNeiU (1966). We divided this set into four subsets of 60 definitions each. Ten subjects (University ofMichigan undergraduates) were assigned to each subset. They read the definitions one by one, trying to write the target word designated by each definition on an answer sheet. When an appropriate word could not be retrieved, the subjects answered "yes" or "no" to the question, " D o you feel that you may know the word later?" After the first pass through each list, we asked the subjects to read again those definitions that were still unfinished, and to report any word retrieved as a response during the second pass. Then a list ofthe actual words targeted by the definitions was presented. The subjects rated their familiarity with each word on a 5-point scale (1 = low, 5 = high), and for each definition not yet completed, they indicated whether any target word on the list was appropriate toit. By using the data from the normative study, we formed a derived set of 84 definitions that appeared to be suitable for our purposes. The words targeted by these definitions had recall probabilities with a range of .0 to .75. The familiarity ratings ranged from 3 to 5. Along with the derived set of 84 definitions,

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20 other definitions were selected from the Nelson and Narens (1980) norms. The words targeted by these definitions had recaU probabilities ranging from .015 to .60. Their median feeling-of-knowing ratines ranged from 3 to 9 on a 9-point scale. Our final overall set of definitions included 104 members. The targeted words contained 4-13 letters each. According to the Thorndike and Lorge (1944) frequency counts, 84 of these words had 0.22-20 occurrences per million, and another 3 of the words fell above that range; no frequency counts were available for the rest ofthe words. A complete listing ofthe selected words and definitions is given in the Appendix. In addition, a set of nonwords for the lexical-decision task was generated by replacing one or two letters of real words with other letters. The resulting nonwords (e.g., trinsfer, dexicon, and institote) were ail pronounceable according to English phonology and had orthographic structures similar to words. Another set of filler words was prepared as well. The range of frequency counts for these words was 0.22-100 per million. Experiment 1 The purpose ofExperiment 1 was to obtain some initial data regarding the feasibility and informativeness of our procedure. We had subjects perform the lexical-decision task after the rareword definition task and feeling-of-knowing judgments, but omitted the final old-new recognition task. A moderate (i.e., about 1 min) time interval was inserted between the presentation of a particular definition and the subsequent lexical decisions about the corresponding target and control words. The chosen interval helped ensure that if any residual activation of inaccessible memory traces was present after the semantic processing of a definition, then it might still be a t a detectable level during the lexical-decision task. Later, in Experiment 2, we significantly lengthened the intervening interval and added the final old-new recognition task as a means of further investigating subjects' performance.

Method Subjects. The subjects were 45 undergraduate students recruited from an introductory-psychology pool at the University of Michigan. One subject was excluded because he produced a high error rate (greater than 30%) on the lexical-decision task. Apparatus. The experiment was conducted in a sound-attenuation booth under the control of a digital computer (DECPDP 11/34). Subjects sat in front ofthe display screen ofthe computer terminal at a viewing distance of approximately 35 cm. Instructions and stimulus materials were presented on the display screen. Subjects entered their responses via the terminal keyboard. Stimuli and design. From the 104 definitions selected in the normarive study, two separate experimental lists that each contained 52 distinct definitions were created for the rare-word definition task. Half of the subjects received List I, and the other half received List 2 (sec Appendix). Corresponding to each list and the definitions on it, there were also 52 different sequences of test stimuli generated for the lexical-decision task. Ail subjects ruade lexical decisions about the items in ail of these sequences, regardless ofwhich definition list was assigned to them. Each sequence consisted of six items, including one target word, one 9 control word, one, two, or three nonwords, and one, two, or three filler words. Neighboring target and control words occurred as matched

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pairs. The target words were the answers to the definitions on a subject's list. The control words were the answers to the de finitions on the other list not seen by that subject. Ail words within a given sequence were the same length. Under this arrangement, exactly the same items served as both target words and control-words across subjects, which helped equate ancillary lexical factors. Some subjects saw the definition ofthe word BANDANNA, for example, and did not see the definition of the word ASTEROID, whereas the opposite was true o f other subjects. Correspondingly, BANDANNA and ASTEROID were, respectively, target and control words in the first case, and the roles of these words were reversed in the second case. As a result, overall differences between performance on the targets and the controls cannot be attributed simply to artifactual differences between the two types ofstimuli. Contingent on certain constraints, the serial positions o f stimulus types (i.e., target words, control words, filler words, and nonwords) within each six-item sequence were counterbalanced across trials. Items in the first two positions o f a sequence always consisted o f fdler words and nonwords, which serval as warm-up stimuli. The target and control words occurred in the remaining four positions, mixed along with other nonwords and filler words. No individual item was presented more than once per subject. Similarly, no definition was presented more than once as part ofthe rare-word definition task. Procedure. Each subject was tested individually in a single session that lasted approximately 75 min. At the start ofthe session, the subject practiced making lexical decisions. On each trial ofthis warm-up phase, a single test stimulus appeared at the center o f the display screen. The slash (/) key ofthe terminal's keyboard was pressed to indicate a positive (word) dr and the z key was pressed to indicate a negative (nonword) decision. Reaction time was measured from the onset o f t h e test stimulus until the response occurred. The stimulus was removed as soon as the subject responded or 2 s elapsed. Following an incorrect response, the message ERROR was displayed for 250 ms. If a response did not occur within 2 s afier the onset of a letter string, error feedback was given. An interval o f I s separated the end o f o n e trial from the beginning o f t h e next. A total of 80 four-letter strings were presented for the practice lexical decisions; half were common English words, and half were pronounceable nonwords. None o f these practice items appeared again during the remainder o f t h e experiment. When subjects had completed the practice lexical-decision task, they were given instructions for the main part o f the experiment involving the rare-word definitions, feeling-of-knowing judgments, and subsequent criterion (lexical decision) test. The instruction period included three trials with materials other than those used in the actual experimental tasks and served to familiarize the subjects with the definition task. The order o f t h e remaining trials was randomized. Subjects were not told that any specific relation existed between the definition task and the subsequent lexical-decision task. Figure 1 shows the sequence of events during a typical trial o f the experiment. Each trial began with a subject pressing the "return" key of the computer terminal to indicate that he or she was ready. Next, a definition from one o f t h e assigned lists appeared at the top o f t h e display screen. After 15 s, a prompt ("THE WORD IS:") to enter the designated word was presented under the definition. Both the definition and the prompt remained on the screen while the subject tried to recall a word and enter a response using the terminal keyboard. The subject was encouraged to enter any word that came to mind and seemed appropriate. There was no specific time limit on responding. Responses typically took l min or less to make. If the subject failed to recall any word in response to the definition, then he or she simply pressed the "return" key. Next the question, "DID YOU ENTER A WORD (Y/N).9'' appeared on the screen. Ifthe subject's answer was positive, then an instruction appeared on the screen saying, "RATE YOUR CONFIDENCE IN THE WORD

YOU ENTERED," and the subject had to make a confidence rating on a scale from 1 to 5 ( 1 = low, 5 = high). The right branch o f Figure 1 was followed after a " n o " answer to the question "DID YOU ENTER A WORD.9" In this case, the subject had to judge how strong Iris or her feeling o f knowing was, despite being unable to recall the word designated by the definition. These judgments were ruade by responding to two additional prompts. One prompt was the question, "IS THE WORD ON THE TIP OF YOUR TONGUE (Y/N).9", it required a yes/no answer. The other prompt was the request, "RATE YOUR FEELING OF KNOW1NG," which required a response on a scale from 1 to 5 ( 1 = love, 5 = high). There were two related goals in taking both measures. First, we used each as a means o f checking the reliability of the other. Second, we combined them subsequently into a composite variable whose predictive value was greater than either of its components alone (see Data analyses). AIter the ratings were finished, the terminal screen was cleared, and the subject prepared for making a sequence o f six lexical decisions. This procedure paralleled the earlier practice phase o f the lexical-decision task. Subjects were instructed to respond as quickly and accurately as possible to each item presented in the sequence. As described earlier (see Stimuli and design), the stimuli included the target word designated by the definition, a matched control word relevant to some definition on the other (unassigned) list, filler words, and nonwords. When the sequence oflexical devisions was finished, the subject rested for a period o f 2 s and then proceeded to the next trial involving another rare-word definifion, feeling-of-knowingjudgment, and lexical-decision

Figure 1. The sequence ofevents on a typical trial in Experiment 1.

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ACTIVATION AND METACOGNITION sequence, as Figure 1 illustrates. Fifty-two trials were included for each subject, corresponding to the 52 definitions on his or her assigned list. Data analyses. A total of 2,288 trials were conducted with the rareword definitions and lexical-decision sequences (44 subjects × 52 definitions per list). The data for each trial consisted of a subject's response to the definition on that trial, his or her ratings concerning the relevant target word, and reaction times of the six lexical decisions made after the definition. To analyze the data, we began by labeling the memory state induced immediately after a definition had been presented on a trial. A correctrecall state was deemed to have occurred if a subject correctly recalled the target word designated by the definition. An incorrect-recall state was deemed to have occurred if the subject recalled some word other than the nominally correct target. A no-recall state was deemed to have occurred when the subject did not recall any word in response to the definition. Subjects exhibited the correct-recall state on 27% of the trials, the incorrect-recall state on 29% of the trials, and the no-recall state on 44% of the trials. All of the possible memory states occurred for each of the subjects. Most of the definitions (91 out of 104) induced all of the states. Given the structure of the data set, we used regression analyses and analyses of variance to assess how the memory states induced by the rare-word definition task affected subsequent performance on the lexical-decision task. In each regression analysis, reaction time was the dependent variable and subjects were independent variables. When subjects exhibited the no-recall state, the feeling-of-knowing ratings and/ or the tip-of-the-tongue answers also served as independent (predictor) variables. Most of the analyses reported for the no-recall state involved combining the tip-of-the-tongue answers and feeling-of-knowing ratings into a composite measure that we call latent accessibility A value of 3 on the latent-accessibility scale corresponded to subjects answering "yes" to the tip-of-the-tongue question and rating their feeling of knowing as high (i.e., 4 or 5) in the no-recall state. A value of I on the latent-accessibility scale corresponded to subjects answering "no" to the tip-of-thetongue question and rating their feeling of knowing as low (i.e., 1 or 2). A value of 2 on the latent-accessibility scale corresponded to all other intermediate response combinations (e.g., "no" to the tip-of-the-tongue question and 3 for the rated feeling of knowing). This let us circumvent some of the inherent unreliability in the rated feelings of knowing and tip-of-the-tongue answers, because subjects' introspective reports about feelings of knowing typically have more than two but fewer than five levels of gradation (Brown & McNeill, 1966; Hart, 1965, 1967; Lathman, Lachman, & Thronesbery, 1979; Nelson, 1984). The analyses of data from the no-recall state were further complemented by nonparametric gamma correlations calculated for each subject separately. Nelson (1984) has recommended the gamma correlation as being particularly well suited to assess effects associated with feelings of knowing, because this statistic only assumes that feelings of knowing constitute an ordinal scale. (For other applications of gamma correlations, see Nelson et al., 1984; Nelson, Leonesio, & Landwehr, 1986; for a detailed comparison of gamma correlations with other covariance measures, see Nelson, 1984.) As part of all data analyses, an attempt was made to remove possible artifactual effects caused by a priori differences in the difficulties of individual words (e.g., systematic variations of word frequency and length). For each word, the reaction times produced in response to it were adjusted by the amount of difference between the mean of those times and the grand-mean reaction time across all words. This kind of adjustment has been found useful by some previous investigators (e.g., Kolers & Palef, 1976; McKoon & Ratcliff, 1980).

Results Three major types of test stimuli were presented in the lexical-decision task: target words, control words, and nonwords.

Table 1

Results From the Lexical-Decision Task: Experiment 1 Stimulus type

Mean RT (ms)

% Errors

Target word Control word Nonword

835 865 988

8.5 16.0 15.6

Mean reaction times o f correct lexical decisions and error rates for each stimulus type are shown in Table 1. O n the average, responses to target words were faster than responses to control words, t(43) = 3.30, p < .005, and error rates were lower, t(43) = 7.80, p < .001. The following subsections focus more specifically on the relation between the subjects' m e m o r y states immediately after the definition task and the reaction times for lexical decisions about the target and control words. Correct- and incorrect-recall states. Performance during the lexical-decision task depended systematically on whether the correct-recaU state or incorrect-recall state was involved. O n trials where the target word was recalled correctly, subjects made faster lexical decisions for it than for a matched control word. The facilitation there was highly significant (mean difference = 121 ___14 ms), t(2100) = 8.5,p < .001. However, on trials in which an incorrect word (i.e., one other than the nominal target) was recalled, the reaction times to make lexical decisions about the correct target word did not differ significantly from the reaction times to make lexical decisions about the control word (mean difference = 9 ___ 12 ms), t(2100) = 0.7, p > .2. These c o m b i n e d results support our expectation that the lexical-decision task may provide a sensitive diagnostic indicator o f the residues left by prior successful and unsuccessful retrieval attempts. No-recall state. M o r e important, some interesting results emerged from trials involving the no-recall state. Figure 2 shows the m e a n reaction times o f lexical decisions about the target and control words separately for the no-recall state as a function o f the latent-accessibility scale described earlier, in which a value o f 3 indicates a "yes" answer to the tip-of-thetongue question and a high feeling-of-knowing rating, and a value o f 1 indicates a " n o " answer to the tip-of-the-tongue question and a low feeling-of-knowing rating (see Data analyses). Again, we found that there was a significant main effect o f word type (target vs. control). When subjects did not produce any response to the rare-word definitions, they were still faster on the average at making subsequent lexical decisions about the target words than about the control words, t(1648) = 1.86, p
.5. No-recall state. W h e n subjects experienced the no-recall state (i.e., did hot produce any item in response to a given definirion), the effect o f word type (target vs. control) on lexical decisions interacted with the measure o f latent accessibility (i.e., c o m b i n e d rip-of-the-tongue answers and feeling of knowing rarings) that we introduced earlier. Figure 4 iUustrates this interaction for the m e a n reaction rimes ofdecisions about unrecalled target words and control words plotted as a function o f latent accessibility, where a value o f 3 indicates that the accessibility was potentially high and a value of I indicates that it was low. A pattern similar to the one in Experiment 1 (Figure 2) again emerged. As before, the target words yielded reacrion rimes having a significant inverse relation to the latent-accessibility scale (linear slope = - 1 7 _ 9 ms per accessibility unit), t(855) = 1.82,p < .05, one tailed; R 2 = .25, whereas the control words did not (linear slope = 2 _+ 9 ms per accessibility unit), t(89 l) = .22, p > .4. This occurred even though a considerably longer temporal interval than in Experiment 1 separated the lexical decisions from the prior definirion task. 3 Correspondingly, for each subject, the g a m m a correlarions between m e a n reaction times and latent accessibility depended on word type (Figure 3). In the case o f target words, the withinsubjects g a m m a correlations averaged - 0 . 1 6 across subjects, t(45) = 1.67, p < .05, one tailed, whereas they averaged only 0.03 in the case o f c o n t r o l words, t(45) = 0.43, p > .3.

Table 4

Results From the Lexical-Decision Task: Experiment 2 Stimulus type

Mean RT (ms)

% Errors

Target word Control word Nonword

781 810 910

13.8 17.1 16.2

3 Similar regression analyses performed with the original feeling-ofknowing ratings also revealed that feeling of knowing was a significant predictor of reacrion rimes. The linear siope for the target words was - 1 2 + 5 ms per feeling-of-knowing unit, t(855) = 2.13, p < .05, R 2 = .25, whereas the slope for the control words was only - 4 _ 6 ms per feeling-of-knowing unit, t(891) = .79, p > .2.

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Results: Old-New Recognition Task The dependent variables of interest from the old-new recognition task inClude the mean reaction rimes and error rates of judgments about the old target words, old control words, and new words, as shown in Table 5. Before analyzing the error rates, vve normalized them with an arcsin transformation. Analyses of variance across ail memory states with word type and subjects as factors revealed that error rates (i.e., incorrect "new" judgments) were lower on the average for old target words than for old control words, F(I, 45) = 22.2, p < .001. Similarly, reaction times were shorter on the average for old target words than for old control words, F(I, 45) = 7.59, p < .01. These effects attributable to word type suggest that residual priming of memory traces during the initial rare-word definition task facilitated subsequent storage ofepisodic information encountered during the lexical-decision task, which in turn facilitated old-new judgments about the stored episodic information. Correct- and incorrect-recall states. As in the lexical-decision task, the effects ofword type (target vs. control) on the reaction times of old-new judgments varied systematically with the memory states induced by the prior definitions. After target words bad been recalled correctly in response to their definitions, correct old judgments about those words were faster than those about the control words (mean difference = 84 _+ 12 ms), /(2005) = 7.05, p < .001. This happened even though subjects saw both types ofwords as part ofthe intervening lexical-decision task, before the old-new recognition task was performed. However, when incorrect (nontarget) items were recalled in response to the definitions, the reaction times of old judgments about the targets tended to be longer than the reaction rimes of old judgments about the control words (mean difference = 20 _+ 13 ms),/(2005) = 1.56,p < .1, one tailed. No-recall state. The mean reaction rimes of old judgments about unrecalled target words and paired controls appear in Figure 5 as a function of out composite latent-accessibilitymeasure. These data were obtained under the no-recaU memory state, in which subjects failed to produce any item in response to the prior definitions. A multiple regression analysis was performed with latent accessibility, word type (target vs. control), and the Latent Accessibility • Word Type interaction as predictors. The analysis showed significant main effects of latent accessibility, t(1702) = 2.58, p < .01, and word type,/(1702) = 2.55, p < .0 l, and a significant interaction between the two factors,/(1702) = 2.96, p < .0 l. This pattern of results closely resembles those obtained during the prior lexical-decision task (cf. Figures 2 and 4). Reaction rimes to recognize old unrecalled target words decreased sub-

Table 5

Results From the Old-New Recognition Task: Experiment 2 Stimulus type

Mean RT (ms)

% Errors

OId target word Old control word New word

797 816 906

16.0 23.0 20.6

Figure 5. Mean reaction times from the old-new recognition task of Experiment 2 ruade by subjects in the no-recall memory state for the target words and control words as a function of latent aecessibility.

stantially as their position on the latent-accessibility scale increased (linear slope --- - 4 0 + 9 ms per accessibility unit), /(836) = 4.25, p < .001, R 2 = .25. The decrease occurred even though an interval of 30 min or more separated subjects' initial exposure to the definitions from their subsequent old-new recognition judgments. Control words did not enjoy such benefit (linear slope = 4 ___ 10 ms per accessibility unit),/(821) = .45, p > .3. 4 G a m m a correlations computed within subjects between mean reaction rimes and latent accessibility further substantiated the latter results (Figure 3). Across subjects, these correlations averaged - 0 . 3 4 for the target words, /(45) = 3.49, p < .001, and only - 0 . 0 4 for the control words,/(45) = 0.43, p > .3.

Discussion Experiment 2 reinforces and extends Experiment 1. The results from both the lexical-decision task and the old-new recognition task (Tables 3-5, Figures 3-5) were very similar to those obtained previously (Tables 1-2, Figure 2-3). After target words had been recalled correctly in the definition task, the reaction rimes to make responses during the subsequent indirect criterion tests were shorter and the error rates were lower for the target words than for control words. Analogous differences 4 A multiple-regression analysis was also performed with feeling of knowing, word type, and the Feeling of Knowing • Word Type interaction as predictors. There were a significant feeling-of-knowingeffect, t(1702) = 3.05, p < .01, a significant word-type effeet t(1702) = 2.07, p < .05, and a significant interaction between feeling-of-knowingand word type t(1702) = 2.55, p < .05. The linear slope for the target words was -26 _+6 ms per feeling-of-knowingunit, t(836) = 4.59, p < .0001, R2 = .26, whereas it was 1 _+6 ms per feeling-of-knowingunit for the control words, t(821) = .21, p > .3.

ACTIVATION AND METACOGNITION between the reaction rimes and error rates for these word types (i.e., targets vs. controls) also occurred when no items were recalled in response to the initial rare-word definirions. However, when subjects recalled other incorrect items instead ofthe target words, the reaction rimes and error rates for the targets were about the saine as, or greater than, those for the control words. Likewise, the subjective feelings of knowing observed here had effects similar to those in Experiment 1. When subjects failed to recall any word for a given definition, their reaction rimes to make subsequent lexical decisions and old-new judgments about the target words were inversely related to their feelings of knowing. Shorter rimes occurred in cases that elicited strong feelings of knowing than in cases that elicited weak feelings. These feelings did not affect performance on the control words, which were irrelevant to the presented definirions. Our findings have at least two interesting implicarions. First, it appears that if temporarily inaccessible memory traces are parrially primed by an initial induction stimulus (e.g., rareword definition), then such priming may later influence both semanric-memory (e.g., lexical decision) and episodic-memory (e.g., old-new recognition) performance. In particular, the better recognirion of old unrecalled target words than of matched control words, foUowing their exposure during the lexical-decision task, can be attributed to enhanced assimilation of temporally dated (i.e., episodic) information. This enhancement, which correlates posirively with prior feelings of knowing, perhaps helps ensure that repeated retrieval failures do not happen once the objective of an unsuccessful retrieval attempt is encountered subsequently. We infer that the encoding processes needed to avoid such failures may be relatively spontaneous and unpremeditated, given that subjects were unaware of the impending old-new recognition task but still benefitted more from making intermediate lexical decisions about the target words than about the control words. Second, it appears that if the rime between an unsuccessful retrieval attempt and a future criterion test is extended, then primed memory traces can still have a significant impact on ulrimate memory performance. We increased the interval between the rare-word definition task and the lexical-decision task by several minutes in Experiment 2. More distracting activity was included during it than in Experiment 1. There was an even longer interval (i.e., 30 min), with more distraction, between the definirion task and the old-new recognirion task. Nevertheless, some facilitarion of criterion-test responses to the inirially unrecalled target words remained. The last outcome casts doubt on the conscious-expectancy hypothesis that we considered previously as a possible account of the results from Experiment 1. According toit, the facilitation of performance achieved through retaining and rehearsing partial fragments ofa target word in short-term memory should essentially vanish when the interval before the criterion test is lengthened by the amount used in Experiment 2. Such lengthening presumably would impose too great a load on the limited capacity of short-term memory for it to continue helping a subject after he or she has processed a number of other irrelevant inputs (Crowder, 1976, chap. 6). The fact that subjects still benefitted from their initial exposures to the rare-word definirions, even after a fairly extended period of rime, points toward an unlimited-capacity mecha-

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nism as one likely source of the observed facilitation (cf. Neely, 1976, 1977; Posner & Snyder, 1975). As we hypothesized previously (Experiment 1, Discussion), the priming oftemporarily inaccessible memory traces may stem at least in part from unconscious automaric spreading activation (Collins & Loftus, 1975; Meyer & Schvaneveldt, 1971, 1976), which is generated when subjects process a diflicult retrieval prompt (e.g., rareword definirion). This activarion could persist in a residual form despite an increase of the load on short-term memory as imposed by Experiment 2. It would provide a potenrial basis both for differential feelings of knowing and for faster lexical decisions about the target words, consistent with the class of traceaccess mechanisms proposed by Nelson et al. (1984). General Discussion From a retrospective standpoint, Experiments 1 and 2 have broadened the apparent sphere of influence attribut,able to feelings of knowing and their underlying mediators. We found that feelings ofknowing elicited in response to diflicult factual probe questions were at least moderately accurate predictors of future memory performance, supporting claims ruade by previous investigators (e.g., Freedman & Landauer, 1966; Gruneberg & Monks, 1974; Hart, 1965, 1967; Nelson et al., 1984; Read & Brute, 1982; Schacter, 1983). Moreover, our results demonstrated reliable metacognirive judgments even when the final criterion tests involved only indirect performance measures obtained through lexical-decision and old-new recognirion tasks. It was not necessary to reconfront subjects with the initial quesfions or make direct references back to their attempted answers. The correlarion between strong feelings and high performance occurred in a seemingly spontaneous and incidental fashion, extending over the domains of both semanric and episodic memory. What we found might, indeed, be taken as further evidence for the inherent integrality ofthese two memory domains (McKoon, Ratcliff, & Dell, 1986; cf. Tulving, 1972, 1986).

Relation to Semantic-Priming Research Given that a process of unconscious automatic spreading acrivarion may account for the present findings, they are especially interesting in light ofpast research on semanric priming. As we noted earlier, semanric-priming research during the last two decades has typicaUy used prime stimuli (e.g., single words, or word combinarions) with close associations to subsequent familiar test srimuli (e.g., first-order free associates), maximizing the prospects of obtaining large facilitation effects (Fischler, 1981). A few studies of this genre have, however, revealed an effect induced by weaker primes through rather remote associations (e.g., Fischler, 1977). On the basis ofthis outcome, spreading activation gained credibility as one significant component of the priming process. Some investigators have even reported facilitarion attributable to spreading activarion under circumstances in which the subjects were nominaUy unaware of the prime srimuli that induced it (Fowler, Wolford, Slade, & Tassinary, 1981; Marcel, 1983). Such results and the present findings could be viewed as complementary, in that they exhibit priming by relatively minimal, perhaps subconscious, retrieval cues. In addition, our results suggest a more extended rime course

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than was previously acknowledged for spreading activation to have its effects. Most studies of lexical-decision making (e.g., Meyer et al., 1972), word naming (e.g., Warren, 1972), and cued word production (e.g., Loftus, 1973) have limited the time between prime stimuli and subsequent test stimuli to 30 s or less. The facilitation found there could not necessarily be assumed to persist over longer intervals of minutes or hours. On the other hand, such an assumption now seems more plausible, because we observed facilitation effects up to at least halfan hour after subjects' original exposure to selected prime stimuli. 5

Relation to Other Memory Phenomena The extended time course of spreading activation may be related to some other well-known memory phenomena. For example, consider the finding known to social psychologists as the Zeigarnik effect, which was first demonstrated by one of Kurt Lewin's students (Zeigarnik, 1927, cited in Baddeley, 1976, p. 269). Zeigarnik's study concerned the memorial consequences of interrupting subjects while they were in the midst of performing a series of challenging manual and intellectual tasks. The tasks included threading beads, learning a poem, and drawing a vase. She allowed the subjects to complete half the tasks, ofwhich there were 22 in ail, but prevented them from finishing the remainder. When subsequently asked to list ail ofthe tasks, the subjects consistently recalled more of the interrupted tasks. Similar effects have been found for the recall of anagrams when attempts to solve them were interrupted (Baddeley, 1963). Zeigarnik's explanation of her effect was that the unfinished tasks caused "unresolved tension," which supposedly served to maintain the memory traces of them at least temporarily. In our own terms, such tension could correspond to residual activation of those traces concerning important task elements. The activation might have significant benefits across a variety oftask domains. Because of it, people would be more prepared to resume a given task after its interruption, and they would perhaps be better able to assimilate intervening information relevant to task completion. Given that Zeigarnik found enhanced recaU of multiple interrupted tasks, it seems likely that several memory traces may remain simultaneously active for a period of time while attention is directed toward other matters. If the hypothesized connection between the Zeigarnik effect and spreading activation is valid, then this could help answer the question of how long the activation of a particular memory trace persists. Follow-up studies of the Zeigarnik effect showed that recall enhancement disappeared after subjects were allowed to complete the formerly unfinished tasks, thus dissipating their "unresolved tensions" (Ovisiankina, 1928, cited in Baddeley, 1976, p. 270). This suggests a possible causal link between task completion and degree of residual activation. Perhaps there is an internal monitor of some kind that checks the status of temporarily suspended endeavors and maintains a modicum of extra activation in their memory traces until they have been completed.

We call this the memory-sensitization hypothesis. According to it, the initial unsuccessful attempt to solve a problem may partially activate stored, but currently inaccessible, memory traces critical to the problem's solution. Then, during a subsequent intervening period of other endeavors, the activation may sensitize a person to chance encounters with related external stimuli that raise the critical traces above threshold and trigger their integration with other available information. As the incubation period increases, the probability of solution could increase as well, even if the residual activation level remains constant or even declines somewhat, because there would be more and more opportunities over time for relevant stimulus encounters. Similar hypotheses have appeared in accounts by other investigators of incubation effects (e.g., Penney & Winsor, 1982; Posner, 1973). To the extent that we found evidence for activation of inaccessible long-term memory traces, which subsequently facilitated stimulus recognition and classification, these accounts now stand on somewhat firmer ground. The memory-sensitization hypothesis is likewise supported by some classic experiments on problem solving. For example, in one well-known study, Maier (1931) asked subjects to solve a problem that involved tying together the loose ends of two strings that were suspended vertically from the ceiling of a test room. The distance between the strings was large enough that a subject could not simply grasp one of the strings and carry it over to the other before tying them together. Instead, the strings could only be tied together by somehow getting both of their ends into the c,enter of the room at the same time while they were angled obliquely with respect to the ceiling. The preferred solution required making one ofthe strings into a pendulum by attaching toit one of several small objects scattered around the room. Afler improvising the swing pendulum, the subject could put it in motion, go quickly over to the other string, pull the other string toward the moving string pendulum, catch the string pendulum as it swung nearby, and then tie the ends of the two strings together. Maier (193 l) found that although the pendulum solution was not easily reached at first, subjects frequently caught on right after they received a subtle hint from the experimenter, who casually brushed against one ofthe strings, setting it gently into motion, which mimicked the swing of a pendulum. This hint triggered the solution very quickly (i.e., within less than a minute), but the assimilation of the hint seemed tobe subconscious. Subjects were unaware ofthe experimenter's directive actions, and did not mention them in retrospective accounts ofhow they arrived at the pendulum solution. FoUowing Maier's (1931) work, Judson et al. (1956) showed that subjects' solutions ofthe two-string problem were also facilitated by the performance of a prior incidental-recall task. They had subjects learn a series of word lists before attempting the problem. No explicit connection was made apparent between the problem and the lists. However, for some subjects, one ofthe lists included the key words string, pendulum, and swing, which provided an indirect hint to the solution. Subjects who received this list later solved the problem more frequently in the preferred manner. Again, the beneficial effects of the hint

Explanation of Incubation Effects in Problem Solving The results of Experiments 1 and 2 also suggest a possible further explanation of incubation effects in problem solving.

5 For additional evidence of persistent facilitation effectsand a discussion of their possible theoretical implications, see Foss (1982).

ACTIVATION AND METACOGNITION

seemed to be subconscious; subjects failed to mention it during their introspective reports. By using another related procedure involving Duncker's (1945) candle problem, Glucksberg and Weisberg (1966) obtained similar results as well, showing subconscious facilitation of solution attempts af~r an incidental exposure to relevant verbal precues. These findings are what we would expect undš the memorysensitization hypothesis. Both the original learning of the keyword list in Judson et al?s (1956) study and the initial problem confrontation in Maier's (1931) study may have partially activated relevant weak memory traces (e.g., the concept of a pendulum). Such activation could provide a basis for assimilating later subtle hints (e.g., the experimenter gently brushing against a string) and/or reaching the preferred solution spontaneously, through fleeting encounters with other external stimuli. It would not necessarily require subjects to have a conscious awareness of what led them to reach their goal. Ifthe memory-sensitization hypothesis is valid, then it would calt for some reformulation ofideas about the nature of incubation effects in problem solving. The term incubation has a popular connotation that people's state ofmind somehow "matures" or "consolidates" gradually over an interval between one attempt and the next to salve a ditl9 problem, much like the physical state of an egg changes gradually during its stay in an incubator before hatching (Posner, 1973, chai). 7). However, the operational definition of"incubation" does not necessarily imply such a gradual change. As we have argued, the passage of time, which offers opportunities for chance external stimulus encounters, could increase the probability of ultimate successfui solutions without any intervening change of mental state, once an initial confrontation with a ditficult problem has partially activated relevant memory traces. The level of activation associated with those traces and the connections between them might remain relatively stable throughout the interim until an appropriate encounter happens to occur. Theoretical Reservations Of course, some investigators might express theoretical reservations about the views outlined here. Several alternative accounts have been proposed to explain the occurrence of incubation effects in problem solving. At the simplest level, an effect of incubation could result from the release of mental or physical fatigue that builds up during intense effort at solving a problem (Silveira, 1971). Underlying knowledge structures might remain constant, but the processing capacity available to deal with them might increase as the fatigue dissipates. At a more complex level, incubation could also involve an unconscious "blind variation" of ideas, in which new, potentially relevant knowledge structures are formed and accepted or rejected over time as potential problem solutions (CampbeU, 1960). Our experiments do not rule out these possibilities. We have only demonstrated the potential impact of memory sensitization, which might operate jointly with other mechanisms. The present demor8 was conducted in a setting in which the information needed to solve a problem (i.e., rare-word definition) was prestored. Subjects were under no obligation to generate entirely new associations among old bits of information. Thus, there remains the question ofwhether other mechanisms

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would contribute to the occurrence of incubation effects when novel solutions are necessary. A question also remains about how feelings of knowing and problem solving are related. Because fe• of knowing may lac based on partial activation ofcurrently inaccessible mœ traces, and because such traces may conceivably contribute to ultimate successful solutions of problems, we would posit that incubation effects and feelings of knowing could be mediated by the hypothesized memory-sensitization process. However, this position is open to debate based on some prior feeling-of-knowing studies. In particular, Metcalfe (1986) presented subjects with "insight" problems such as the sixteen-dot puzzle, which requires an array of sixteen dots to be connected by six contiguous line segments. After a brief exposure to a problem, the subjects had to judge how likely they were to eventually solve it. Metcalfe hypothesized that these judgments ("warmth" ratings) might be made analogously to ones obtained in the typical feeling-ofknowing memory paradigm, but contrary to this hypothesis, her data revealed only a marginal positive correlation between the predicted and actual solution rates. The correlation was much higher for feelings of knowing induced by ditticult general-information questions in a standard recall task. Consequently, she inferred that feelings of kno~5ng and their underlying mediators, although undoubtedly relevant to basic memory performance, perhaps have little to do with insightful problem solving (cf. Weisberg & Alba, 1981). This inference, which contrasts with our account of incubation effects based on memory sensitization, merits further study. Although Metcalfe's (1986) correlations between feelings of knowing and problem-solution rate were quite low, they did exhibit some positive trends. The lack of higher correlations may bave stemmed in part from the fact that her subjects received only a brief (viz., 5-s) exposure to the problems before having to make their judgments. ƒ brief exposures could preclude the activation and/or metacognition of relevant stored information, which might otherwJse become more influential after a longer period of time. It is also possible that higher correlations between feelings of knowing and solution rates would emerge in response to some types ofproblems other than those used by Metcalfe (1986). Her problem domain was a relatively restricted one, consisting primarily of geometric puzzles with limited semantic content and seemingly little relation to past experience. A richer domain might leave more avenues open for feelings ofknowing to contribute toward successfui solution attempts. Conclusion In conclusion, the preceding discussion calls for further work with an elaborated version of the feeling-of-knowing paradigm and stimuli drawn from different domains, not just rare-word definitions or simple puzzles. We need to study more carefuUy the role played by activation and metacognition oftemporarily inaccessible stored information under conditions in which problem solutions are hOt entirely prestored, but may be generated by integrating diverse bits of information in long-term memory. Perhaps by using indirect criterion tests such as the lexical-decision and old-new recognition tasks, it will become

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clearer how m e m o r y sensitization and other related mechanisms yield unanticipated products ranging from the recall of forgotten names (James, 1890/1950) to the clever p r o o f of mathematical theorems (Poincar› 1952) and the tying together of loose ends (Maier, 1931). References Baddeley, A. D. (1963). A Zeigarnik-like etfect in the recall ofanagram solutions. Quarterly Journal of Experimental Psycholog~, 15, 63-64. Baddeley, A. D. (1976). The psychology ofmemory New York: Basic Books. Brown, R., & McNeill, D. (1966). The "tip ofthe tongue" phenomenon. Journal of Verbal Learning and Verbal Behavior, 5, 325-337. Campbell, D. T. (1960). Blind variation and selective retention in creative thought as in other knowledge processes. PsychologicalReview, 67, 380--400. Collins, A. M., & Loftus, E. E (1975). A spreading-activation theory of semantic processing. PsychologicalReview, 82, 407--428. Crowder, R. (1976). Principles oflearning and memory. Hillsdale, N J: Erlbaum. Duncker, K. (1945). On problem solving. Psychological Monographs, 58 (5, Whole No. 270), Fischler, I. (1977). Associative facilitation without expectancy in a lexical decision task. Journal of Experimental Psychology." Human Perception and Performance, 3, 18-26. Fischler, I. ( 1981 ). Research on context effects in word recognition: Ten years back and forth. Cognition, 10, 89-95. Foss, D. J. (1982). A discourse on semantic priming. Cognitive Psycholog~, 14, 590-607. Fowler, C. A., Wolford, G., Slade, R., & Tassinary, L. (1981). Lexical access with and without awareness. Journal ofExperimental Psychology: General, 110, 341-362. Freedman, J. L., & Landauer, T. K. (1966). Retrieval of long-terre memory: "Tip-of-the-tongue" phenomenon. Psychonomic Science, 4, 309-310. Fulgosi, A., & Guilford, J. P. (1968). Short-term incubation in divergent production. American Journal of Psycholog~, 81, 241-246. Gick, M. L., & Holyoak, K. J. (1980). Analogical problem solving. Cognitive Psychology, 12, 306-355. Glucksberg, S., & Weisberg, R. W. (1966). Verbal behavior and problem solving: Some effects of labeling in a functional fixedness problem. Journal of Experimental Psycholog~, 71, 659-664. Gruneberg, M. M., & Monks, J. (1974). "Feeling ofknowing" and cued recall. Acta Psychologica, 38, 257-265. Gruneberg, M, M., Monks, J., & Sykes, R. N. (1977). Some methodological problems with feeling of knowing studies. Acta Psychologica, 41, 365-371. Hart, J. T. (1965). Memory and the feeling-of-knowing experience. Journal of Educational Psychology, 56, 208-216. Hart, J. T. (1967). Memory and the memory-monitoring process. Journal of Verbal Learning and Verbal Behavior, 6, 685-691. James, W. (1950). Principles ofpsychology (Vol. 1). New York: Dover Publications. (Original work published 1890). Judson, A. J., Cofer, C. N., & Gelfand, S. (1956). Reasoning as an associative process: II. "Direction" in problem solving as a function of reinforcement of relevant respon~s. PsychologicalReports, 2, 501507. Koestler, A. (1964). The act ofcreation. New York: Dell. Kolers, E A., & Palef, E R. (1976). Knowing not. Memory& Cognition, 4, 553-558. Koriat, A., & Lieblich, I. (1974). What does a person in a "TOT" state know that a person in a "don't know" state doesn't know. Memory & Cognition, 2, 647-655.

Koriat, A., & Lieblich, I. (1977). A study of memory pointers. Acta Psychologica, 41, 151-164. Lachman, J. L., Lachman, R., & Thronesbery, C. (1979). Metamemory through the adult lifespan. Developmental Psycholog~, 15, 543-551. Lot'tus, E. E (1973). Activation of semantic memory. American Journal of Psychology, 86, 331-337. Maier, N. R. E (1931). Reasoning in humans. II. The solution ofa problem and its appearance in consciousness. Journal of Comparative Psycholog~, 12, 181-194. Marcel, A. J, (1983). Conscious and unconscious perception: Experiments on visual masking and word recognition. Cognitive Psycholog~, 15, 197-237. McClelland, J. C., & Rumelhart, D. E. (1981). An interactive activation model of context effects in letter perception: Part I. An account of basic findings. PsychologicalReview, 88, 375--407. McKoon, G., & Ratcliff, R. (1980). Priming in item recognition: The organization of propositions in memory for text. Journal of Verbal Learning and VerbalMemorg, 19, 369-386. McKoon, G., Ratcliff, R., & Dell, G. S. (1986). A critical evaluation of the semantic-episodic distinction. Journal of Experimental Psychology: Learning, Memo~ and Cognition, 12, 295-306. Metcalfe, J. (1986). Feeling of knowing in memory and problem solving. Journal of Experimental Psychology: Learning, Memo~ and Cognition, 12, 288-294. Meyer, D. E., & Schvaneveldt, R. W. (1971). Facilitation in recognizing pairs of words: Evidence of a dependence between retrieval operations. Journal of Experimental Psycholog~, 90, 227-234. Meyer, D. E., & Schvaneveldt, R. W. (1976). Meaning, memory structure, and mental processes. Science, 192, 27-33. Meyer, D. E., Schvaneveldt, R. W., & Ruddy, M. G. (1972, November). Activation oflexical memory. Paper presented at the meeting of the Psychonomic Society, St. Louis, Missouri. Meyer, D. E., Schvaneveldt, R. W., & Ruddy, M. G. (1975). Loci of contextual effects on visual word recognition. In P. M. A. Rabbitt & S. Dornic (Eds.), Attention and performance X (pp. 98-118). London: Academic Press. Monsell, S., & Banich, M. T. (1982, November). Lexicalpriming. Repetition effects across input and output modalities. Paper presented at the meeting of the Psychonomic Society, Minneapolis, Minnesota. Morton, J. (1969). Interaction of information in word recognition. Psychological Review, 76, 165-178. Murray, H. G., & Denny, J. P. (1969). Interaction of ability level and interpolated activity (opportunity for incubation) in human problem solving. PsychologicalReports, 24, 271-276. Neely, J. H. (1976). Semantic priming and retrieval from lexical memory: Evidence of facilitatory and inhibitory processes. Memory & Cognition, 4, 648-654. Neely, J. H. (1977). Semantic priming and retrieval from lexical memory: Roles ofinhibitionless spreading activation and limited-capacity attention. Journal of Experimental Psychology: General, 106, 226254. Nelson, T. O. (1984). A comparison ofcurrent measures ofthe accuracy of feeling-of-knowing predictions. Psychological Bulletin, 95, 109133. Nelson, T. O., Geder, D., & Narens, L. (1984). Accuracy of feeling-ofknowing judgments for predicting perceptual identification and relearning. Journal of Experimental Psychology: General, 113, 282-

300. Nelson, T. O., Leonesio, R. J., & Landwehr, R. S. (1986). A comparison ofthree predictors of an individual's memory performance: The individual's feeling of knowing versus the normative feeling of knowing versus base-rate item difliculty. Journal ofExperimental Psychology: Learning, Memor~, and Cognition, 12, 279-287. Nelson, T. O., & Narens, L. (1980). Norms of 300 general information

ACTIVATION AND METACOGNITION questions: Accuracy of recall, latency of recall, and feeling-of-knowing ratings. Journal of Verbal Learning and Verbal Behavior, 19, 338-368. Norman, D. A., & Bobrow, D. G. (1976). On the role of active memory processes in perception and cognition. In C. N. Cofer (Ed.), The structure ofhuman memory (pp. 114-132). Sala Francisco: Freeman. Patrick, C. (1937). Creative thought in artists. Journal of Psycholog)g, 4, 35-73. Penney, C. G., & Winsor, B. (1982, November). Incubation viewed as a retrieval phenomenon. IMper presented at the meeting of the Psychonomic Society, Minneapolis, Minnesota. Poincar› H. (1952). Mathematical creation. In B. Ghiselin (Ed.), The creativeprocess (pp. 36-37). New York: Mentor. Posner, M. l. (1973), Cognition: An introduction. Glennview, IL: Scott and Foresman. Posner, M. I., & Snyder, C. R. R. 0975). Facilitation and inhibition in the processing of signais. In E M. A. Rabbitt & S. Dornic (Eds.), Attention and performance V (pp. 669-682). New York: Academic Press. Read, J. D., & Bruce, D. (1982). Longitudinal tracking ofdit~cult memory retrievals. Cognitive Psycholog?z, 14, 280-300. Scarborough, D. L., Cortese, C., & Scarborough, H. S. (1977). Frequency and repetition effects in lexical memory. Journal of Experi-

mental Psychology: Human Perception and Performance, 3, l - 17. Schacter, D. L. (1983). Feeling of knowing in episodic memory. Journal

of Experimental Psychology: Learning, Memor~, and Cognition, 9, 39-54. Schuberth, R. E., & Eimas, E D. (1977). Effects ofcontext on the classification ofwords and nonwords. Journal of ExperimentalPsychology: Human Perception and Performance, 3, 27-36. Silveira, J. M. (1971). Incubation: The effect of timing and length on problem solution and quality of problem processing. Unpublished master's thesis, University of Oregon.

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Slamecka, N. J., & Graf, E (1978). The generation effect: Delineation of a phenomenon. Journal of Experimental Psychology: Human Learning and Memo~ 4, 592-604. Thorndike, E. L., & Lorge, I. (1944). The teacher's word book of 30,O00 words. New York: Columbia University Press. Tulving, E. (1972). Episodic and semantic memory. In E. Tulving and W. Donaldson (Eds.), Organization ofmemory (pp. 381-403). New York: Academic Press. Tulving, E. (1986). What kind of a hypothesis is the distinction between episodic and semantic memory? Journal of Experimental Psychology: Learning, MemooE and Cognition, 12, 307-31 l. Tulving, E., & Gold, C. (1963). Stimulus information and contextual information as determinants of tachistoscopic recognition of words. Journal of Experimental Psychology, 66, 319-327. Tulving, E., & Pearlstone, Z. (1966). Availability versus accessibility of information in memory for words. Journal of Verbal Learning and Verbal Behavior, 5, 381-39 l. Wallas, G. (1926). The art ofthought. New York: Harcourt, Brace. Warren, R. (1972). Stimulus encoding and memory. Journal of Experimental Psychology, 94, 90-100. Weisberg, R. W., & Alba, J. W. (1981). An examination ofthe alleged foie of"fixation" in the solution of several "insight" problems. Journal of Experimental Psychology: General, 110, 169-192. Wellman, H. M. (1977). Tip of the tongue and feeling of knowing experiences: A developmental study of memory monitoring. Child Developinent, 48, 13-2 l. Yaniv, I., & Meyer, D. E. (1985, May). Activation and incubation revealed by a problematic memory-retrieval task. Paper presented at the meeting of the Midwestern Psychological Association, Chicago, Illinois.

Appendix Definitions and Target Words Below are the 104 definitions and target words used in Experiments I and 2, separated according to the two lists on which they appeared. For each definition, the word within parentheses at the end is the designated target, and the adjacent two-digit number is an index used to denote how the target words were paired with other control words. Ifa particular target word on one list (e.g., SEXTANT)has the saine numerical index (e.g., 01) as a target word (e.g., VERTIGO)on the other list, then these two words served as the paired eontrols for each other across subjects assigned the different lists.

AN A N I M A L ABLE T O LIVE B O T H O N L A N D A N D IN WATER; AIRCRAFq" DESIGNED T O TAKE-OFF F R O M A N D A L I G H T O N EITHER L A N D O R WATER; FLAT B O T I ' O M E D VEHICLE ABLE T O MOVE IN WATER A N D O N LAND. (6 AMPHIBIAN) A SMALL PLANET; ONE O F T H E T H O U S A N D S O F SMALL PLANETS BET W E E N MARS A N D J U P I T E R W I T H DIAMETERS F R O M A F R A C T I O N O F A MILE T O N E A R L Y 500 MILES. (7 ASTEROID) A STYLE O F ARTISTIC EXPRESSION P R E V A L E N T IN T H E 17TH C E N T U R Y T H A T IS M A R K E D G E N E R A L L Y BY E X T R A V A G A N T F O R M A N D ELABORATE O R N A M E N T A T I O N , ESP. IN MUSlC A N D ARCHITECTURE. (8 BA-

Definition List 1 A N A V I G A T I O N A L I N S T R U M E N T USED IN M E A S U R I N G A N G U L A R DISTANCES, ESP. T H E A L T I T U D E O F T H E SUN, M O O N A N D STARS A T SEA. ( l SEXTANT) A SMALL BOAT USED IN T H E RIVER A N D H A R B O R TRAFFIC O F C H I N A A N D JAPAN, PROPELLED W I T H AN OAR. (2 SAMPAN) AN INFECTIOUS A N D U S U A L L Y FATAL BACTERIAL DISEASE O F ANIMALS, ESP. CA'I-I'LE A N D SHEEP. (3 A N T H R A X ) A PERSON W H O BELIEVES T H A T N O T H I N G C A N BE K N O W N A B O U T GOD; EXPRESSING I G N O R A N C E O F GOD; N O T AN ATHEIST. (4 AGNOSTIC) IN O L D G R E E K STORIES, T H E F O O D O F T H E GODS; SUPPOSED T O GIVE I M M O R T A L I T Y T O A N Y H U M A N W H O ATE IT; A N Y T H I N G T H A T HAS A D E L I G H T F U L TASTE. (5 AMBROSIA)

ROQUE) T H E CAPITAL O F SYRIA. (9 DAMASCUS) B U I L D I N G IN W H I C H MUSLIMS W O R S H I P ALLAH. ( l0 MOSQUE) A SOVIET T R A V E L E R B E Y O N D T H E E A R T H ' S ATMOSPHERE; ASTRON A U T . (1 l C O S M O N A U T ) ILLEGAL TRADE; S M U G G L I N G G O O D S I N T O O R O U T O F A C O U N T R Y , C O N T R A R Y T O T H E LAW. ( 12 C O N T R A B A N D ) A STATE O F BEING UNABLE T O FEEL PAIN, HEAT, ETC.; BRANCH 1N C H E M I S T R Y C O N C E R N E D W l T H SUBSTANCES P R O D U C I N G THIS STATE. ( 13 ANESTHESIA) A W O R D MADE BY C H A N G I N G T H E O R D E R O F THE LETTERS IN ANO T H E R W O R D ; E.G. P L U M - L U M P . ( 14 A N A G R A M ) T H E FIRST N A M E O F T H E C H A R A C T E R 'SCROOGE' IN DICKENS' "A CHRISTMAS CAROL". ( 15 EBENEZER)

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GOBLET, CONSECRATED CUP, WINE CUP, ESP. ONE USED IN C H U R C H FOR C O M M U N I O N . ( 16 CHALICE) A NEW CONVERT, ESP. A N E W L Y BAPTIZED CHRISTIAN; GENERALLY, A BEGINNER O R NOVICE. ( 17 NEOPHYTE) A M I X T U R E O F METALS, ESP. A METAL O F L O W Q U A L I T Y W I T H A METAL O F H I G H E R VALUE. ( 18 ALLOY) A G R O T E S Q U E CARVED O R SCULPTED F I G U R E P R O J E C T I N G AT T H E

T H E ZEPPELIN T H A T E X P L O D E D IN L A K E H U R S T N.J. IN 1937. (48 HINDENBURG) T H E MOST P O P U L A R PIN-UP G I R L O F W O R L D W A R Il. (49 GRABLE) T H E CAPITAL O F AUSTRALIA. (50 CANBERRA) LISTLESSNESS; STATE O F A P A T H Y O R INDIFFERENCE. (51 L E T H A R G Y ) F O R M A T I O N O F W O R D S IN I M I T A T I O N O F N A T U R A L SOUNDS. (52 ONOMATOPOEIA)

UPPER PART O F A BUILDING, USUALLY FROM A R O O F G U T T E R . (19 GARGOYLE)

Definition List 2

A FANATICAL PARTISAN; ONE W H O IS CARRIED A W A Y IN HIS P U R S U I T O F A CAUSE O R OBJECT. (20 ZEALOT) A N OBJECT BELIEVED BY PRIMITIVE PEOPLE T O HAVE MAGICAL

POWER T O P R O T E C T O R A I D ITS OWNER; A N OBJECT O F SPECIAL DEVOTION. (21 FETISH) A U T H O R I Z E D PERIOD O F DELAY IN P E R F O R M A N C E O F A LEGAL OBLIG A T I O N O R THE P A Y M E N T O F A DEBT; A W A I T I N G PERIOD SET BY AN A U T H O R I T Y ; A SUSPENSION O F ACTIVITY. (22 M O R A T O R I U M )

DIZZINESS O R S W I M M I N G O F T H E HEAD; GIDDINESS; NAUSEA; N O T DRUNKENNESS. ( 1 VERTIGO) AN I N S T R U M E N T H A V I N G F R O M 30 T O 40 STRINGS OVER A S H A L L O W H O R I Z O N T A L S O U N D I N G BOX, A N D PLAYED W I T H PICKS A N D FINGERS; N O T A HARP. (2 ZITHER) T H E CAPITAL O F BURMA. (3 R A N G O O N ) UNSELFISH BENEVOLENCE, GENEROSITY. PRINCIPLE O F C O N S I D E R I N G

OFFICER W H O ACTS AS A GO-BETWEEN FOR T W O ARMIES. (23 LIAISON)

T H E WELL BEING A N D HAPPINESS O F O T H E R S FIRST; UNSELFISHNESS. (4

PICTURE W R I T I N G USED BY A N C I E N T EGYPTIAN PRIESTHOOD. (24 HI-

ALTRUISM)

EROGLYPHIC) ANY O F THE N U M E R O U S E X T I N C T PLEISTOCENE ELEPHANTS DISTING U I S H E D FROM RECENT ELEPHANTS BY LARGE SIZE, VERY L O N G TUSKS T H A T C U R V E UPWARDS, A N D WELL-DEVELOPED BODY HAIR. (25 MAMMOTH) THE TECHNICAL T E R M I N O L O G Y O R CHARACTERISTIC I D I O M O F A SPECIAL ACTIVITY O R G R O U P ; A N OBSCURE A N D OFYEN P R E T E N T I O U S LANG U A G E M A R K E D BY C I R C U M L O C U T I O N S A N D L O N G WORDS. (26 JARGON) PUZZLE; AN OBSCURE SPEECH O R WRITING; S O M E T H I N G H A R D T O UND E R S T A N D O R EXPLAIN; AN INSCRUTABLE O R MYSTERIOUS PERSON. (27 ENIGMA) A STYLE O F COOKING; M A N N E R O F P R E P A R I N G FOOD. (28 CUISINE) T R U N K O F A STATUE W l T H HEAD A N D LIMBS MISSING. (29 TORSO) STRENGTH, STAYING POWER, ENDURANCE. (30 STAMINA) FIFTIETH ANNIVERSARY O F AN EVENT; ITS C O M M E M O R A T I O N , O R CELEBRATION. (31 JUBILEE) COMBAT BETWEEN M O U N T E D K N I G H T S W l T H WEAPONS SUCH AS LANCES, SWORDS, O R BATTLE-AXES, ESP. AS P A R T O F A T O U R N A M E N T . (32 JOUST) BRANCH O F Z O O L O G Y DEALING W l T H BIRDS. (33 O R N I T H O L O G Y ) A PERSON W H O APPEALS T O PEOPLE'S PREJUDICES, M A K I N G FALSE CLAIMS A N D PROMISES IN O R D E R T O G A I N POWER; FALSE LEADER O F PEOPLE. (34 D E M A G O G U E ) A T R A C K CONTEST CONSISTING O F TEN DIFFERENT TRACK-ANDFIELD EVENTS (35 D E C A T H L O N ) T O PLACE SIDE BY SIDE; P U T CLOSE T O G E T H E R . (36 JUXTAPOSE) T H E FIRST ARTIFICIAL SATELLITE P U T IN O R B I T BY RUSSIA IN 1957. (37 SPUTNIK) THE A U T H O R O F T H E B O O K ' 1984". (38 ORWELL) THE APOLLO L U N A R M O D U L E T H A T L A N D E D THE FIRST M A N O N T H E MOON. (39 EAGLE) THE CAPITAL O F CANADA. (40 OTTAWA) T H E C O U N T R Y O F W H I C H B A G D A D IS T H E CAPITAL. (41 IRAQ) LAST NAME O F BATMAN'S SECRET I D E N T I T Y IN T H E BATMAN COMICS. (42 WAYNE) SEDIMENT DEPOSITED BY R U N N I N G WATER. (43 SILT) THE CHAPEL WHOSE CEILING WAS P A I N T E D BY MICHELANGELO. (44 S1STINE)

T H E CAPITAL O F FINLAND. (5 HELSINKI) W I T H I D E N T I T Y CONCEALED; DISGUISED. (6 I N C O G N I T O ) LARGE B R I G H T C O L O R E D H A N D K E R C H I E F .

BRIGHTLY COLORED

SQUARE O F M A T E R I A L W I T H RED O R Y E L L O W SPOTS USUALLY W O R N R O U N D T H E NECK. (7 B A N D A N N A ) T H E ACT O F AN A U T H O R I T Y BY W H I C H P A R D O N IS G R A N T E D T O A LARGE G R O U P O F INDIVIDUALS; G E N E R A L P A R D O N , ESP. FOR OFFENSES A G A I N S T T H E STATE. (8 AMNESTY) FISSURE, N A R R O W O P E N I N G IN A ROCK, WALL, ETC., R E S U L T I N G F R O M A SPLIT O R CRACK. (9 CREVICE) T H E F R E N C H A U T H O R O F "THE PLAGUE'. ( 10 CAMUS) INCAPABLE O F BEING EXPRESSED IN WORDS; INDESCRIBABLE; UNSPEAKABLE O R UNUTTERABLE; INEXPLICABLE; INEXPRESSIBLE. (11 INEFFABLE) T O EXPOSE M1LI~ CHEESE, O R F E R M E N T E D LIQUIDS T O A H I G H TEMP E R A T U R E BUT BELOW T H E BOILING P O I N T F O R A GIVEN PERIOD O F TIME, K I L L I N G BACTERIA A N D ARREST1NG FERMENTATION. (12 PASTEURIZE) MADE O R D O N E O N O R AS IF O N T H E S P U R O F T H E MOMENT; IMPROVISED; C O M P O S E D O R U T T E R E D W I T H O U T PREVIOUS PREPARATION; EXTEMPORANEOUS. ( 13 I M P R O M P T U ) H A R D E N E D , UNFEELING, O R I N D I F F E R E N T T O lNSULTS A N D THE SUFF E R I N G O F OTHERS. ( 14 CALLOUS) A MONSTER, H A L F B U L L T H A T WAS C O N F I N E D IN A L A B Y R I N T H W H E R E IT C O N S U M E D ITS T R I B U T E O F A T H E N I A N Y O U T H S A N D MA1DENS, U N T I L SLAIN BY THESEUS. (15 M I N O T A U R ) A R I G I D AIRSHIP O F A LARGE DIRIGIBLE TYPE. ( 16 ZEPPELIN) BESTOWAL O R I N V O C A T I O N O F DIVINE FAVOR. (l 7 BLESSING) A H I D I N G PLACE USED BY EXPLORERS F O R C O N C E A L I N G O R PRESERVI N G PROVISIONS O R IMPLEMENTS. ( 18 CACHE) BELIEF T H A T EVENTS ARE D E T E R M I N E D BY FORCE BEYOND H U M A N CONTROL; A D O C T R I N E T H A T EVENTS ARE F I X E D IN ADVANCE FOR ALL TIME IN SUCH A M A N N E R T H A T H U M A N BEINGS ARE POWERLESS T O C H A N G E THEM. (19 FATALISM) T H E DENSE, FIBROUS, OPAQUE, WHITE, O U T E R C O A T O F THE EYEBALL. (20 SCLERA) T H E CAPITAL O F THAILAND. (21 B A N G K O K ) A C H A R T E R O F LIBERTIES T O W H I C H T H E ENGLISH BARONS FORCED K I N G J O H N T O GIVE HIS ASSENT IN 1225; A D O C U M E N T C O N S T I T U T I N G A F U N D A M E N T A L G U A R A N T E E O F RIGHTS. (22 MAGNA-CARTA)

OPPOSITION T O WAR O R VIOLENCE AS A MEANS O F SETTLING DIS-

A C E R E M O N I A L EMBRACE; A C E R E M O N Y O R SALUTE T O M A R K T H E

PUTES; REFUSAL T O BEAR ARMS O N M O R A L O R RELIGIOUS G R O U N D S .

CONFERRING OF KNIGHTHOOD, OR MARKING THE RECOGNITION OF

(45 PACIFISM)

SPECIAL MERIT; AWARD, AN EXPRESSION O F PRAISE. (23 ACCOLADE)

LAST NAME O F THE M A N W H O ASSASSINATED PRESIDENT J O H N F. KENNEDY. (46 OSWALD) AN EXPERT IN CHILDREN'S DISEASES. (47 PEDIATRICIAN)

T H E SCIENCE O F COINS. (24 NUMISMATICS) A CONNOISSEUR O F F O O D A N D D R I N K . (25 G O U R M E T ) SORCERER; ONE SKILLED IN MAGIC; MAGICIAN. (26 W I Z A R D )

ACTIVATIONAND METACOGNITION

205

SHALLOW BODY OF WATER, NEAR OR CONNECTED TO A LARGER BODY OF WATER. (27 LAGOON)

FROM STEM TO STERN ALONG THE B o T r o M AND SUPPORTING THE WHOLE FRAME. (41 KEEL)

HOME SICKNESS; AN EXCESSIVELY SENTIMENTALCONDITION YEARN-

THE RUBBER ROLLER ON A TYPEWRITER. (42 PLATEN) HEATHEN; IDOLATER OR WORSHIPER OF MANY GODS. (43 PAGAN) ANIMAL OR PLANT LIVING ON ANOTHER; TOADY; SYCOPHANT. (44 PARASITE)

ING FOR RETURN TO OR OF SOME PAST PERIOD OR IRRECOVERABLE CONDITION. (28 NOSTALGIA) SMALL GROUP, OFTEN OF MILITARY OFFICERS, THAT RULES A COUNTRY AFTER A COUP ]D'ETAT AND BEFOR‚ A Lƒ GOVERNMENT IS FORMED; USED ESP. IN CENTRAL AND SOUTH AMERICA, (29 JUNTA) A MYTHICAL FIGURE, HALF MAN, HALF HORSE. (30 CENTAUR) A STATEMENT THAT 15 SEEMINGLY CONTRADICTORY OR OPPOSED TO COMMON SENSE AND YET IS PERHAPS TRUE. (31 PARADOX) DWARF; AN AGELESS AND OFTEN DEFORMED MAN OF FOLKLORE

OEHE THREE-LEAF CLOVER THAT IS THE EMBLEM OF IRELAND. (45 SHAMROCK) THE COUNTRY OF WHICH BUDAPEST IS THE CAPITAL. (46 HUNGARY) THE PROPER NAME FOR A BADMINTON BIRD, (47 SHUTTLECOCK) THE MOUNTAtN RANGE IN WHICH MOUNT EVEREST IS LOCATED. (48 HIMALAYAS)

RIGHT TO EXERCISE LEGAL AUTHORITY OR THE TERRITORY OVER WHICH AUTHORITY IS EXERCISED. (33 JURISD1CTION)

FORMER MEASURE OF DISTANCE, EQUAL TO ABOUT THREE MILES; USED NAUTICALLY. (49 LEAGUE) THE KIND OF POISON SOCRATES TOOK AT HIS EXECUT1ON. (50 HEMLOCK)

COLLECTOR AND DISPOSER OF REFUSE; ANIMAL THAT DEVOURS REFUSE AND CARRION. (34 SCAVENGER)

LARGE TENT, ESP. ONE SOPPORTED ON POSTS OR A TEMPORARY OPEN BUILDING FOR SHELTER, ENTERTAINMENT ETC. (51 PAVILLON)

99 AGENT; ANY OF NUMEROUS SYNTHETIC,WATERSOLUBLE OR LIQUID ORGANIC PREPARATIONS THAT ARE ABLE TO ‚ OILS, AND HOLD DtRT IN SUSPENSION. (35 DETERGENT)

THE PROCESS BY WHICH PLANTS MARE THEIR FOOD. (52 PHOTOSYNTHES1S)

WHO LIVES IN THE EARTH AND GUARDS PRECIOUS ORES OR TREASURFS. (32 GNOME)

THE ACT OF TALKING TO ONESELF; A DRAMATIC MONOLOGUE THAT GIVES THE ILLUSION OF BEING A SERIES OF UNSPOKEN REFLECTIONS. (36 SOLILOQUY) FALSE TESTIMONY WHILE UNDER OATH. (37 PERJURY) THE FIRST SIGNER OF THE "DECLARAT1ON OF INDEPENDENCE'. (38 HANCO99 SOCRATES" MOST FAMOUS STUDENT. (39 PLATO) THE AUTHOR WHO WROTE UNDER THE PSEUDONYM OF MARK TWAIN. (40 CLEMENS) CHIEF AN D LOWEST TI MBE R OR STEEL PLATE OF A VESSEL EXTENDING

Practice Definitions MONEY ALLOWANCE PAID BY A MAN TO HIS W1FE OR FORMER WIFE BY A JODGE'S ORDER, E.G, AFTER DIVORCE. (1 ALIMONY) A SECRETION FROM THE SPERM OF A WHALE, USED IN THE MANUFACTURE OF PERFUME. (2 AMBERGRIS) LOSS OF POWER OR SENSATION OF" MOVEMENT IN PARTS OF TUE BODY. (3 PARALYSIS)

Received September 18, 1985 Revision received August 3 l, 1986 9