Effects of attentional load and ageing on word-stem

EUROPEAN JOURNAL OF COGNITIVE PSYCHOLOGY, 2000, 12 (3), 395± 412

EŒects of attentional load and ageing on word-stem and word-fragment implicit memory tasks David Clarys, Michel Isingrini, and AureÂlie Haerty UniversiteÂ FrancË ois Rabelais, Tours, France

The joint eŒects of reduced attention and age on repetition priming in implicit memory tests of word-fragment completion (WFC) and word-stem completion (WSC) were investigated. An attention load during the study phase reduced the extent of repetition priming in the WSC condition but not in WFC. This ® nding provides support for the view that WSC and WFC involve diŒerent processes. However, there was no evidence of an age eŒect on either of these two types of implicit tasks. The data also revealed an overall signi® cant eŒect of age and reduced attention on explicit cued recall tasks.

Over the past 15 years, a large body of research in cognitive psychology and neuropsychology has focused on the distinction between explicit and implicit memory tests (Roediger & McDermott, 1993; Schacter, 1987). Explicit memory tests such as free recall, cued recall, and recognition are based on the intentional, conscious recollection of a previous experience, and are measured by having subjects think back about some prior event and report on it. In contrast, implicit memory tests measure performance facilitation due to the prior presentation of stimuli, but without intentional or conscious recollection of the experience (e.g., Schacter, 1987). Interest in priming tasks has increased as a result of several studies showing that performance on implicit and explicit memory tests can be dissociated. Studies of patients with organic amnesia, who are severely

Requests for reprints should be addressed to D. Clarys, Laboratoire de Psychologie ExpeÂrimentale, UPRES 2114, UniversiteÂ de Tours, 3 rue des Tanneurs, B.P. 4103, 37041 Tours cedex 1, France. Email: clarys@ univ-tours.fr This research was supported by the ``SanteÂ et socieÂteÂ: Vieillissement individuel et socieÂtal’ ’ program of the French National Research Centre (CNRS). The authors thank Michael Burton, Ricardo Russo and an anonymous reviewer for helpful comments on an earlier version of this paper.

2000 Psychology Press Ltd http://www.tandf.co.uk/journals/pp/09541446.html

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impaired on standard explicit memory tasks, indicate normal priming when the memory task is implicit (Graf, Squire, & Mandler, 1984; Jacoby & Witherspoon, 1982; Shimamura & Squire, 1984). A number of experimental variables appear to have diŒerential eŒects on explicit and implicit memory performance (for a review, see Roediger & McDermott, 1993). For instance, varying the amount of semantic processing at encoding time (by manipulating the levels of processing, for example) has substantial eŒects on many explicit memory tests, but little or no eŒect on many implicit ones (Graf & Mandler, 1984; Jacoby & Dallas, 1981; but see Challis & Brodbeck, 1992, for an exception). Conversely, similarity between the physical features of the stimuli presented at study time and those presented at test time appears to have a strong impact on many implicit memory tests, but little or no eŒect on explicit ones (Craik, Moscovitch, & McDowd, 1994; Rajaram & Roediger, 1993; Roediger & Blaxton, 1987). Such dissociations are very important from the theoretical standpoint because they seem to indicate that explicit and implicit memory tasks involve diŒerent memory systems or memory processes (Graf & Mandler, 1984; Roediger, Weldon, & Challis, 1989; Tulving & Schacter, 1991). One of the variables that has dissociative eŒects on explicit and implicit memory tests is the manipulation of attentional resources during study. Research on this topic has led to the idea that encoding processes that are attention or resource demanding are necessary for explicit memory (e.g., Fisk & Schneider, 1984), whereas less attention-demanding encoding processes may su ce for implicit memory (e.g., Eich, 1984). Some studies have demonstrated that divided attention during encoding impairs explicit test performance but may leave the amount of priming unaŒected. This has been demonstrated for implicit word-fragment completion (Parkin, Reid, & Russo, 1990), picture-fragment completion (Parkin & Russo, 1990; Russo & Parkin, 1993), lexical decision making (Smith & OscarBerman, 1990), and category exemplar generation (Isingrini, Vazou, & Leroy, 1995). In these studies, divided attention was found to lower performance on direct tests such as recognition memory (Parkin et al., 1990), recall (Parkin & Russo, 1990; Russo & Parkin, 1993), and cued recall (Isingrini et al., 1995). These ® ndings have led some authors to suggest that performance on implicit tests largely re¯ ects automatic encoding processes, whereas performance on explicit tests is crucially dependent upon controlled processes that require attentional resources (Graf & Mandler, 1984; Isingrini et al., 1995; Parkin & Russo, 1990). Such hypotheses also appeared consistent with results of studies involving the process-dissociation procedure (PDP; Jacoby, 1991). Rather than identifying controlled (conscious or explicit) and automatic (unconscious or implicit) memory processes with performance on explicit and implicit

ATTENTION, AGEING, AND IMPLICIT MEM ORY

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tests, respectively, the PDP postulates a way to assess the contributions of these two bases for responding within a single task. Studies using this procedure have found suggestive evidence indicating that only controlled in¯ uences of memory were reduced by dividing attention at study time (Jacoby, Toth, & Yonelinas, 1993; Jenning & Jacoby, 1993). However, it is not altogether clear whether we should assume that manipulating attention will have no eŒect on any implicit memory measures. Some studies have found performance declines on implicit memory tasks thought to depend primarily on conceptual rather than perceptual processing. Perceptual priming occurs in tests where the stimulus presented during the learning phase is shown on the test in a perceptually related but degraded or partial form (e.g., perceptual identi® cation tasks, word-fragment completion tasks, and word-stem completion tasks). Implicit conceptual tests, on the other hand, provide information that is related conceptually to the studied information but has no perceptual similarities (as in free association, category association, and category exemplar generation). The utility of making the distinction between these two kinds of implicit tests is supported by the ® nding that experimental manipulations can be used to dissociate the perceptual versus conceptual forms of implicit tests. Researchers have reported that unlike implicit perceptual tasks, elaborate encoding processes (e.g., levels of processing, generation, and organisation) in¯ uence priming on conceptual tests (Hamman, 1990; Rappold & Hashtroudi, 1991; Srinivas & Roediger, 1990). In line with this ® nding, recent studies on attention demands at encoding time have shown that divided attention during the study phase reduces performance on conceptual implicit memory tests such as category exemplar generation, word association, and general knowledge tests, but not on perceptual implicit memory tests like word-fragment completion (Mulligan, 1997, 1998; Mulligan & Hartman, 1996). A similar pattern of results was also recently observed by Schmitter-Edgecombe (1999) in a study involving the PDP. This author has shown that automatic in¯ uences of memory remained invariant across a manipulation of attention during study time for a perceptually driven stem cued-recall task, but was signi® cantly reduced for conceptually driven category name cued-recall task. This pattern of results supports the general conclusion that perceptual priming requires few if any attentional resources but conceptual priming relies heavily on them (Light & Prull, 1995; Mulligan, 1998). However, studies have suggested that diŒerences by manipulation of attention at study time may also have dissociative eŒects on implicit perceptual completion tasks such as word-fragment completion (WFC) and word-stem completion (WSC). In WFC, the individual is presented initially with a complete word, and then, at test time, is given a sampling

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of the word’ s letters (e.g., soldier; _o__i_r); in WSC the study phase is the same, but the ® rst three letters of the word are presented on the test (e.g., soldier; sol____). In both cases, the test instructions are to respond with the ® rst word that comes to mind. Wolters and Prinsen (1997, Exp. 1) found that dividing attention at study time reduced performance on a perceptual word-stem completion test. In line with this ® nding, the neuropsychological literature suggests that WSC may be mediated by frontal-lobe or executive functions. A signi® cant correlation between WSC and performance on the Wisconsin Card Sorting Test (WCST), which measures frontal-lobe function, was observed in normal old people by Davis et al. (1990). More recently, Winocur, Moscovitch, and Stuss (1996) used WFC and WSC on the same sample of subjects and found that only WSC was correlated with WCST performance. Such data suggest that repetition priming involves diŒerent mechanisms in WFC and in WSC, and that attentional or executive resource demands are a factor that mediates priming on WSC alone. Accordingly, one can expect that reducing attention at encoding time will have an eŒect on the WSC task only. The primary purpose of the present experiment was to validate this hypothesis by measuring WSC and WFC on the same subject sample and with use of the same materials. Age-related diŒerences between WSC and WFC have also been reported. Normal ageing is accompanied by less accuracy on explicit measures of memory, and preserved abilities on most implicit memory tasks (for reviews, see La Voie & Light, 1994), but there are notable exceptions for the WSC task. The results for this task are contradictory: some studies have reported a signi® cant age eŒect (Chiarello & Hoyer, 1988; Davis et al., 1990; Hultsch, Masson, & Small, 1991; Small, Hultsch, & Masson, 1995; Winocur et al., 1996 for institutionalised older subjects), whereas others have not (Eustache et al., 1995; Java & Gardiner, 1991; Light & Singh, 1987; Nicolas, Ehrlich, & Facci, 1996; Park & Shaw, 1992; Winocur et al., 1996 for community-dwelling participants). However, comparisons of old and young people on implicit WFC tests reliably show no diŒerences (Jelicic, Craik, & Moscovitch, 1996; Light, Singh, & Capps, 1986; Small et al., 1995; Winocur et al., 1996). The second main purpose of this study was thus to analyse the hypothesis of a dissociative eŒect of age on WSC and WFC when the two tasks involved the same group of subjects and the same words. Moreover, one possible explanation of why age diŒerences in priming may occur only on WSC tasks could be that this age eŒect is related to the attention demands of this task. As is frequently claimed, if older adults have limited processing resources, one can expect that, when compared with young adult controls, elderly performance will decline on memory tasks involving attentional processes. For this reason, one can hypothesise that


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WSC is aŒected by ageing because of reduced attentional resources in the elderly. Then, in respect of an age eŒect, a secondary aim was to examine the idea that reduced attentional resources in older subjects can be a reliable factor of age diŒerences in WSC priming. If this is true, we can expect to ® nd a signi® cant interaction between age and attention such that age diŒerences are greater under reduced attention condition than under full attention condition. In summary, the present study compared groups of young and old adults on implicit word-fragment completion (WFC) and word-stem (WSC) completion tasks, and on word-fragment and word-stem cued recall tasks, under full and reduced attention conditions at encoding time. Our main goals were (1) to con® rm the selective-attention and age-related eŒect on WSC but not on WFC, and, if successful, (2) to determine whether the age eŒect on WSC is related to the reduced attentional resources of older people. Furthermore, in the light of the ® ndings in the memory literature, we did not expect age or reduced attention at encoding time to have diŒerential eŒects on explicit tests cued by word stems or word fragments. Our attention manipulating procedure was similar to the one used by Mulligan (1997). Attention at encoding time was varied by controlling the short-term memory load. Prior to seeing each study word, the subject was presented with no attention load (full attention condition) or a ® vecharacter string load (reduced attention condition). The digits and letters in the string were to be retained in memory until a recall signal was given a few seconds later, and while the study word was being displayed. Mulligan (1997) found that a load of ® ve items caused a large performance decline on an implicit memory test on category exemplar generation. METHOD Subjects A total of 48 subjects living in a medium-sized metropolitan area served as participants. They formed two adult age groups. The younger group consisted of 24 non-students (14 females, 10 males) whose mean age was 30.83 (SD = 4.12). The older group consisted of 24 subjects (14 females, 10 males) with a mean age of 74.66 (SD = 7.16). On average, the younger adults had more education (10.25 years, SD = 1.39) than the older ones (8.00 years, SD = 0.29), t(46) = 7.75, p .001. But, the two groups did not diŒer on the Mill Hill Vocabulary Test (mean = 23.95, SD = 4.71 for the young; mean = 24.25, SD = 4.25 for the old),

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t(46) = ± 0.22. Every older subject obtained a Mini-Mental State Exam (MMSE; Folstein, Folstein, & McHugh, 1975) score above the cut-oŒof 27 points. All participants reported being in good health and said they were not taking any medication likely to aŒect cognitive behaviour. The participants were volunteers and were tested individually. Design and material For both implicit and explicit memory, the experiment included one between-subject factor (age) and two within-subject factors (type of learning: no attention load vs attention load; type of memory test: wordfragment completion vs word-stem completion). The design was a 2 (Age) 2 (Type of Learning) 2 (Type of Test) mixed design. Two study lists of 32 seven- or eight-letter common nouns were used equally often in each group (e.g., Appendix). No two words had the same stem-cue letters or fragment-cue letters. The word-frequency means of the two lists were comparable. Twelve additional items were chosen: four presented before the list as practice items, and four at the beginning and end of each list as primary and recency buŒers. The words were presented in a booklet, with each target item printed in uppercase letters on a 16 6 cm page. Within each target list, the words were randomly divided into two subsets of 16 items. The sets were balanced across encoding conditions (full attention, reduced attention) and test conditions (WFC, WSC, WF cued recall, and WS cued recall) so that each word would be presented equally often in each experimental condition. Which words served as targets and which words served as baseline items was also counterbalanced across subjects. In the attention load condition, the study items were preceded by the presentation of a string of ® ve characters (letters or digits) constructed by randomly selecting items from a set of digits (1± 9) and a set of letters (B, C, D, F, G, H, J, K, L) according to the following rules: (1) the ® rst character was a digit and the letters and digits occupied alternating positions in the string, and (2) no digit or letter was repeated within the same string. It was assumed that using these materials and rules would help to minimise chunking. Procedure The experiment consisted of a study task and four memory tests, two implicit (WSC and WFC) and two explicit (WS cued recall and WF cued recall). At the beginning of the experiment, subjects were informed that the study was designed to provide baseline materials for future research. The purpose of this mildly deceiving statement was to prevent partici-


401

pants from engaging in encoding strategies in anticipation of later retrieval requirements, and to encourage them to view later tasks as unrelated to earlier ones (until explicit memory measures were taken). Each study trial began with the 2.5 s presentation of a 16 6 cm white card showing either a ® ve-character string (in the attention load condition) or a dash (in the no-load condition). For the load trials, subjects were instructed to read the character string aloud and remember it until the ``RECALL’’ signal was given. For the no-load trials, subjects were simply instructed to say ``blank’ ’ in response to the white card. Next the study word was presented for 5 s. Subjects were instructed to look at each word carefully, read it aloud. No mention was made of any subsequent memory tests. Finally, either the word RECALL (in the load condition) or the word BLANK (in the no-load condition) appeared for 2.5 s. Subjects were instructed either to recall the digit and letter string (in the load condition) or to again say ``blank’ ’ (in the no-load condition). Loaded and non-loaded trials were randomly mixed. The implicit word completion task was separated from presentation of the study list by a ® ller task in which subjects were required to complete word stems or word fragments that served as cues to the name of a city; 5 min were allocated for the ® ller task. Then came the implicit completion test, which lasted 5 min. Participants were told they would be presented with incomplete words (a fragment or a stem) and that they had to complete each one with the ® rst word that came to mind, although they were also told that proper nouns were not acceptable. The participant was given an answer sheet consisting of 64 incomplete words: 32 were letter cues for the studied word (16 stems and 16 fragments) and 32 were cues for control words the participants had not seen before (16 stems and 16 fragments). The control words were included to provide baseline estimates of word completion. After the implicit completion test, all participants were asked whether they had noticed that they were generating previously seen list members and whether they deliberately tried to do so. Any subject who answered ``yes’ ’ to the latter question would be eliminated from the experiment (all subjects in fact answered ``no’ ’). Subjects who answered ``yes’ ’ to the ® rst question were designated as `àware subjects’ ’. Finally, a cued recall test was given as a measure of explicit memory. Subjects were told that they would now take a memory test for the words they were shown earlier on the study list. An answer sheet that listed the 32 letter cues (16 fragments and 16 stems) corresponding to the studied words was provided. Using the letter cues to remind them of the study list words, the subjects were asked to complete the cues only with words they remembered, and not to guess. No time limit was set for this task.

402


RESULTS For the study task, the mean recall rates on attention load items were .96 (SD = .03) and .88 (SD = .08) for the young and elderly groups, respectively. A t-test comparison indicated that performance was signi® cantly worse for the elderly subjects, t(46) = 4.15, p .001. The overall results for the experimental phase are summarised in Table 1 and in Table 2, which give the performance on the word completion and cued recall tests, respectively, as a function of age, type of test, and learning condition. The word completion and cued recall data were analysed in separate analyses of variance (ANOVA). Word completion For the two completion tests, the dependent measure was the amount of priming (the diŒerence between the completion rates of studied and nonstudied words). For both age groups and for all within-subject conditions (full vs reduced attention, and WSC vs WFC), signi® cantly more studied words than non-studied words were completed. All t-tests were signi® cant at p .01. Thus, a signi® cant implicit memory eŒect TABLE 1 Means and standard deviations of proportion correct on word-fragment completion and word-stem completion implicit memory tasks in young and older adults

Ð Task Fragment completion Baseline Non-loaded Target Priming Loaded Target Priming Word-stem completion Baseline Non-loaded Target Priming Loaded Target Priming

Younger (n = 24) Ð Ð Ð Ð Ð Ð Ð Ð M SD Ð

Older (n = 24) Ð Ð Ð Ð Ð Ð Ð Ð M SD

0.25

0.18

0.14

0.15

0.43 0.18

0.23 0.23

0.31 0.17

0.16 0.16

0.45 0.20

0.18 0.21

0.26 0.12

0.17 0.19

0.08

0.09

0.11

0.12

0.31 0.23

0.20 0.19

0.31 0.20

0.16 0.12

0.22 0.14

0.14 0.15

0.22 0.11

0.15 0.17


403

TABLE 2 Means and standard deviations of proportion correct on word-fragment cued recall and word-stem cued recall in young and older adults

Ð Task Fragment cued recall Non-loaded Loaded Stem cued recall Non-loaded Loaded

Younger (n = 24) Ð Ð Ð Ð Ð Ð Ð Ð M SD

Older (n = 24) Ð Ð Ð Ð Ð Ð Ð Ð M SD

0.64 0.54

0.18 0.19

0.39 0.37

0.22 0.17

0.42 0.32

0.23 0.21

0.31 0.27

0.19 0.13

occurred in both age groups, in both attention conditions, and on both implicit tests. An ANOVA on the word completion data revealed a main eŒect of attention load, F(1, 46) = 4.78, p .03, indicating that reducing attention at encoding time lowered word completion performance. There was also a signi® cant interaction between attention load and type of implicit word completion test, F(1, 46) = 4.55, p .03, indicating that only performance on the WSC implicit memory task was aŒected by the attention load. No other eŒects approached signi® cance, F(1, 46) = 1.70 for age, F(1, 46) = 0.001 for type of implicit task, F(1, 46) = 0.48 for interaction between age and attention load, and F(1, 46) = 0.04 for interaction between age and type of implicit task. A separate ANOVA on the WFC data revealed that neither the main eŒect of age, F(1, 46) = 0.84, of attention demand, F(1, 46) = 0.29, nor that of interaction between age and attention load was signi® cant, F(1, 46) = 1.63. However, on the WSC test, the main eŒect of attention load, F(1, 46) = 8.29, p .001, was signi® cant, but the age eŒect, F(1, 46) = 0.91, and the interaction between age and attention load, F(1, 46) = 0.006, were not. A more detailed look at the data showed that the largest age-related diŒerence was in the loaded learning condition of the WFC, contrary to our hypothesis (.20 for the younger group and .12 for the older group). However, this diŒerence did not reach signi® cance, t(46) = 1.41. The lack of an interaction between the attention condition and age is di cult to evaluate, because there was an age diŒerence favouring the young on the recall rate of items loaded during study. Such an age diŒerence could arise either because the older subjects had more di culty on this short-term memory task or because they devoted proportionately less eŒort to the attention load task. The latter explanation could be the

404


reason why there was no signi® cant age eŒect on WSC under loaded attention conditions. To control for a possible eŒort eŒect on the diŒerence between young and old people on memory of loaded items, the ANOVA was re-computed with loaded task performance as a covariate variable. When we did this, none of the analysis of variance, particularly the age eŒect on WSC, F(1, 46) = 0.53, gave diŒerent outcomes. An additional ANOVA with `àware’ ’ versus `ùnaware’ ’ subjects as a between-subject factor on the WSC yielded no reliable eŒect of the awareness factor, F(1, 46) = 1.47, and no interaction between awareness and attention, F(1, 46) = 1.91. These results suggest that the eŒect of reduced attention on WSC is not a function of greater explicit memory leakage. Cued recall For word completion cued recall, the dependent measure was the studieditem recall rate on the word fragment and word stem tasks. The ANOVA yielded a signi® cant main eŒect of age, F(1, 46) = 12.60, p .001, revealing reduced performance with age, as well as a signi® cant eŒect of attention load, F(1, 46) = 8.72, p .01, indicating a decrease in the number of words recalled in the loaded condition. There was also a signi® cant eŒect of task indicating that performance was worse on the WS cued-recall test, F(1, 46) = 33.00, p .001. In addition, the interaction between age and type of task was reliable, F(1, 46) = 6.26, p .05, showing that the performance of the elderly subjects was aŒected less on WS cued recall than on WF cued recall. The results indicated ® nally that neither the interaction between age and attention load, F(1, 46) = 2.09, nor the one between type of task and attention load, F(1, 46) = 0.11, was signi® cant. DISCUSSION The major feature of interest in the present study was that it examined the way in which implicit memory task performance (WFC and WSC) is aŒected by age and by diŒerences in attention load during learning. The results showed that WSC and WFC respond diŒerently to manipulations of attention: reduced attention during study decreased priming on the WSC test but not on WFC. They also showed that ageing made no diŒerence in these two implicit tasks. These ® ndings are consistent with previous results showing that WSC requires attentional processing (Wolters & Prinsen, 1997, Exp. 1), whereas WFC does not (Mulligan, 1998; Mulligan & Hartman, 1996). They therefore provide additional support for the view that priming in WFC and WSC can be dissociated.


405

However, they did not con® rm the hypothesis that WSC and WFC tests respond diŒerently to variations in age. The ® nding that reduced attention is a factor that can be used to dissociate two presumably perceptually based implicit memory tasks is important, since it goes against the traditional view that automatic processes are associated only with implicit memory tasks, and that controlled processes are associated with conscious recollection. They also limit the generality of the view that a reduced attention eŒect will be obtained only on concept-driven implicit memory tests (Mulligan, 1998; Mulligan & Hartman, 1996). Such a result thus seems to be consistent with Winocur et al.’s (1996) hypothesis that automatic processes and controlled processes contribute to conscious recollection and implicit memory. However, one possible artifactual explanation for why WSC might be aŒected by manipulation of attention at study time is based on the idea of contamination by deliberate recollection. Spontaneous test awareness during implicit testing may sometimes prompt subjects to adopt explicit recollection (e.g., Schacter, Bowers, & Booker, 1989). If such contamination did occur, it might be responsible for the eŒect of attentional manipulation in WSC. In a recent study, to verify this hypothesis, Wolters and Prinsen (1997, Exp. 2) used a variant of the PDP that allowed them to control for intentionally explicit memory responses but also for `ìnvoluntary explicit responses’ ’ Ð that is, items that are unintentionally retrieved but consciously remembered (Schacter et al., 1989). This is also a conscious memory eŒect that may cause parallel eŒects of experimental manipulations on explicit and implicit memory tests. They found a large eŒect of attentional manipulation on the controlled memory component, whereas the automatic memory component was not aŒected. This ® nding is consistent with the view that attention eŒects on implicit stem completion tasks can be explained by explicit retrieval contamination. In this account our data showing a diŒerential eŒect of reducing attention at study on WSC and WFC imply that episodic memory contamination for list words would be more bene® cial to word stem completion than to word fragment completion. Such a hypothesis needs to be tested. However, considering that subjects designated as `àware’ ’ are supposed to be those that produce more explicit responses in implicit memory tasks, the fact that, in our experiment, the eŒect of reduced attention did not appear to be reliably related to the subjects’ awareness argues against the explicit contamination account. A second explanation for the reduced attention eŒect on the WSC test is based on the distinction between perceptually driven and conceptually driven priming tasks. On the basis of this distinction, Mulligan and Hartman (1996) argued that attention eŒects at encoding time can be

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expected to be similar to level-of-processing eŒects because both manipulations aŒect the amount of semantic or conceptual processing. The fullattention condition should require more semantic and conceptual processing, whereas the reduced-attention condition should con® ne encoding operations to those necessary for stimulus identi® cation. As such, both the processing level and attention at encoding time should aŒect conceptdriven implicit tests but not data-driven ones. This view is consistent with ® ndings demonstrating a conceptual versus perceptual implicit task dissociation linked to attention (Mulligan, 1998; Mulligan & Hartman, 1996) or level of processing (Hamman, 1990; Rappold & Hashtroudi, 1991; Srinivas & Roediger, 1990). Although WSC has been regarded as a perceptually driven task (Roediger & McDermott, 1993), it is unlikely that it is purely so. Our data, which demonstrated a reliable attention eŒect on WSC, suggest that this task has a conceptual component, and that WFC is solely perceptual. The nature of the word-stem completion task is in fact open to question. Some researchers have argued that it is primarily perceptual, whereas others contend that it is mainly conceptual (see Gabrieli et al., 1994; Keane, Gabrieli, Fennema, Growdon, & Corkin, 1991; Roediger, Weldon, Stadler, & Riegler, 1992). If word-stem completion is conceptual, then attention and processing level can be expected to have an impact on this task because of its concept-driven component. Although this account seems to provide a parsimonious explanation of the present data, it must be regarded with caution when considered in the context of level-of-processing eŒects. The literature provides no clear results indicating that the processing level has a signi® cant eŒect on WSC (Graf & Mandler, 1984; Roediger & McDermott, 1993). Thus, further research is needed to clarify the status of WSC in the classi® cation of implicit memory test, and to understand why this task appears to be attention demanding, apparently without being in¯ uenced by manipulation of the processing level. Another possible explanation for the dissociative attention eŒect on WFC and WSC may relate to the lexical-perceptual view (Jenkins, Russo, & Parkin, 1998; Richardson-Klavehn & Gardiner, 1998; Weldon, 1998). According to this view, the study of Richardson-Klavehn and Gardiner (1998) provides evidence that depth-of-processing eŒects observed on perceptual priming tasks can re¯ ect lexical processing rather than conceptual processing. Consistent with this interpretation their data have shown, by using three types of encoding orienting tasks (perceptual, lexical, and semantic), that conceptual processing and lexical processing produce equivalent amounts of priming in a WSC task, both superior to the perceptual study processing. Such a ® nding is consistent with the suggestion of Weldon (1991) that lexical access at encoding is necessary for


407

perceptual implicit memory in a WSC task. Moreover, in a recent study, Crabb and Dark (1999), using a focused attention task, have shown that implicit memory probably re¯ ects initial attentional processing necessary to elicit lexical processing. Thus, with respect to the dissociative eŒect of attention on WFC and WSC tasks, one can hypothesise ® rst that lexical access at encoding may require attention and second that not all perceptual implicit tasks re¯ ect lexical encoding processing. Our results should suggest that WSC tasks require this processing but not WFC tasks. This hypothesis should be tested in further research. It seems, however, in line with the view developed by Winocur et al. (1996), that, despite stem and fragment completion being similar in that both include a perceptual component, and both tests require participants to produce the ® rst word that comes to mind, they diŒer in the types of processes evoked by the separate cues. These authors argued that, because in word-stem completion there is a generate component, this task biases the participant to search the lexicon for a word beginning with the stem. In contrast, they supposed that word-fragment completion does not evoke this strategy because unlike initial stems, letters drawn randomly from the word are poor cues for locating words in the lexicon. Then, fragment completion can be best viewed as a perceptual identi® cation test in which the fragments evoke the perceptual record of the target. With regard to ageing, our data do not con® rm that ageing has a diŒerent eŒect on WSC and WFC when these tasks are examined on the same sample of subjects. However, they are consistent with several ® ndings showing that repetition priming in both WFC (Jelicic et al., 1996; Light et al., 1986; Winocur et al., 1996) and WSC (Eustache et al., 1995; Java & Gardiner, 1991; Light & Singh, 1987; Nicolas et al., 1996; Park & Shaw, 1992; Winocur et al., 1996 for community-dwelling older subjects) is preserved in old age. In line with this idea, our data con® rm and extend previous reports and the general view of spared older-adult performance on implicit perceptually driven tasks in conjunction with impaired performance on explicit memory tasks. Moreover, given the hypothesised age-related ine ciency of controlled processing, it was expected that older people would show a greater de® cit in WSC, which is attention demanding, than in WFC, which is not. This result was not obtained. No age diŒerences were observed on either implicit memory task (WSC or WFC), and there was no indication that the magnitude of the reduced attention eŒect for WSC priming was larger for the old than for the young subjects. These data along with the fact that in implicit cued-recall tasks there was also no evidence that loading attention during encoding results in more cost to memory performance for older adults appeared inconsistent with the reduced attentional resource view of cognitive ageing. However, this ® nding is in line with previous results

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indicating that memory decrements resulting from dividing attention at encoding did not diŒer between younger and older adults (e.g., Anderson, Craik, & Naveh-Benjamin, 1998). Considering that the older subjects of our experiment were not institutionalised, the present ® nding appeared consistent with Winocur et al.’ s (1996) results, using a similar procedure in which WSC and WFC were examined on the same sample of subjects. Thus, Winocur et al. (1996) showed that diŒerences between young and older subjects appeared for an institutionalised group of older subjects but not for a communitydwelling group. With the available data, it is di cult to explain why some studies have obtained a signi® cant eŒect of age on WSC whereas others have not. Hultsch et al. (1991) noted that the eŒect is weak and shows up only when the sample size is large. This may be the reason why it did not appear in our study. Another possibility based on Winocur et al.’s (1996) results is that the age eŒect on WSC occurs only for older subjects with frontal dysfunction. Manuscript received May 1999 Revised manuscript received December 1999

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APPENDIX List 1 aquarium (aquarium) brasier (blaze) brugnon (nectarine) capuche (hood) chassis (frame) corniche (cornice) eÂcharpe (scarf) eÂcouteur (earphone) embarras (obstacle) eÂpinard (spinach) faubourg (suburb) giro¯ e (cloves) hanneton (cockchafer) hautbois (oboe) intestin (intestine) litieÁre (litter) magicien (magician) meÂlodie (melody) notaire (notary) oŒrande (oŒering) paravent (folding screen) peÂniche (barge) peuplier (poplar) plumeau (feather duster) polochon (bolster) pupitre (desk) roitelet (wren)

List 2 agreÂ ment (pleasantness) batterie (battery) boussole (compass) cellier (store-room) chignon (chignon) clavecin (harpsichord) crochet (hook) deÂ barras (junk room) eÂ pervier (sparrow-hawk) escalope (escalope) estomac (stomach) ® celle (string) fougeÁ re (fern) freÂ gate (frigate) globule (corpuscle) gourmet (gourmet) impasse (dead end) librairie (bookshop) liquide (liquid) merisier (cherry) musette (haversack) ombrelle (parasol) peluche (plush) phalange (phalanx) pivoine (peony) pruneau (prune) roulotte (caravan)

412


salaire (salary) stature (stature) tapette (carpet beater) termitte (termite) verteÁbre (vertebra)

salsi® s (salsify) soucoupe (saucer) tumulte (commotion) torture (torture) vitamine (vitamin)