Discourse Processes
ISSN: 0163-853X (Print) 1532-6950 (Online) Journal homepage: http://www.tandfonline.com/loi/hdsp20
Accessing the discourse representation during reading Jerome L. Myers & Edward J. O'Brien To cite this article: Jerome L. Myers & Edward J. O'Brien (1998) Accessing the discourse representation during reading, Discourse Processes, 26:2-3, 131-157, DOI: 10.1080/01638539809545042 To link to this article: http://dx.doi.org/10.1080/01638539809545042
Published online: 11 Nov 2009.
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DISCOURSE PROCESSES, 26(2&3), 131-157 Copyright © 1998, Lawrence Erlbaum Associates, Inc.
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Accessing the Discourse Representation During Reading Jerome L. Myers Department of Psychology University of Massachusetts
Edward J. O'Brien Department of Psychology University of New Hampshire
The process of text comprehension requires the integration of the information in the sentence currently being read with information previously read. This, in turn, implies that information presented earlier in the text must be accessed. We present a view of that access process as one in which concepts and propositions in the discourse representation resonate in response to related elements in the current sentence, initiating a process that makes available a subset of the information in the representation. In support of our position, we summarize the effects of several variables that have been shown to affect the availability of information in the discourse representation, and we describe a simulation model of the hypothesized resonance process, together with the results of several applications of that model.
The comprehension of a sentence involves more than understanding the meaning of individual words or even their relation to each other. Comprehension requires that the information in a sentence be integrated with information presented earlier in the text. This, in turn, frequently involves the reactivation of concepts and propositions presented earlier in that text. For example, distant information is often reactivated in response to the reader's need to find the antecedent to an anaphoric reference (Dell, McKoon, & Ratcliff, 1983; O'Brien, Duffy, & Myers, 1986) or in response to the reader's need to find a cause for an action that is otherwise not well motivated (Klin, 1995; Klin & Myers, 1993; Trabasso & Suh, Correspondence and requests for reprints should be sent to Jerome L. Myers, Department of Psychology, Tobin Hall, University of Massachusetts, Box 37710, Amherst, MA 01003-7710, or to Edward J. O'Brien, Department of Psychology, University of New Hampshire, Durham, NH 03824. E-mail:
[email protected] (Jerome L. Myers) or
[email protected] (Edward J. O'Brien)
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1993). Information presented earlier in a text may be reactivated even when the text is locally coherent, and there is thus no need for a conscious search for information related to the current input (Albrecht & Myers, 1995; Albrecht & O'Brien, 1993; McKoon, Gerrig, & Greene, 1996; Myers, O'Brien, Albrecht, & Mason, 1994). According to a memory-based text processing view (McKoon et al., 1996), concepts and propositions currently in working memory make contact with other concepts and propositions processed earlier and, thus, initiate a process by which some subset of earlier information becomes available to the reader for possible integration with what is currently being read. We agree, and in this article, we consider the process by which information read earlier is accessed as well as the factors that influence that process. Our approach is consistent with that presented in Kintsch's (1988) discussion of his construction-integration (C-I) model. Kintsch noted that "there is a basic, automatic construction-plus-integration process that normally is sufficient for comprehension. This process is more like perception than problem solving" (p. 168). Sanford (1990) also argued that the default mechanism that underlies comprehension is "a fast pattern-matching facility" (p. 527) and, like Kintsch, assumed that only when this fails does the reader engage "a slower, classical inference engine" (p. 527). In this article, we present evidence for, and a model of, this pattern-matching facility. The model is based on the assumption that concepts and propositions derived from the sentence currently being processed (the focal sentence), or residing in working memory as a result of reading earlier portions of text, serve as signals to the memory representation. The intensity of these signals may depend on the degree of attention given to the text elements they reflect, but the process initiated by the signals is not under the control of the reader; it proceeds autonomously. As in many models of memory (e.g., Hintzman, 1986; Ratcliff, 1978) and classification (e.g., Estes, 1994; Medin & Schaffer, 1978; Myers, Lohmeier, & Well, 1994), we assume that this process is one in which concepts and propositions in the discourse representation and in the reader's knowledge base resonate as a function of the degree of match to the input. This match depends on the overlap of semantic and contextual features among concepts and on the argument overlap of propositions. Memory elements that are contacted by the initial signal in turn signal to other memory elements. During this resonance process, activation builds, and when the process stabilizes, the most active elements enter working memory. There are two critical features of the resonance process. First, it is continual; a signal is constantly being sent to all of memory. What is resonating in long-term memory changes constantly with each change in the contents of active memory. Thus, what is active in memory is in a constant state of flux (although for the sake of simplicity, our current instantiation assumes the signal is cyclical, and changes in activation are only measured at the end of each cycle). Second, the resonance process is dumb. Information that resonates sufficiently is returned to
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working memory independent of whether that information will ultimately facilitate or hinder further processing. Presumably, there is a second process that continually evaluates the contents of working memory. This process may register failure in certain circumstances, for example, when an anaphoric reference fails to produce an appropriate antecedent, when there is more than one candidate antecedent, when no cause is activated for an action or event described by the focal sentence, or when propositions in working memory contradict each other. When the resonance process fails to provide sufficient information for comprehension to proceed smoothly or when it activates information that disrupts comprehension, there are several options. Readers may refocus on the current contents of working memory, sending new signals to memory; they may engage in some form of problem solving; or they may read the next clause or sentence. The choice made will depend on the reader's motivation, or "standard of coherence" (van den Broek, Risden, & Husebye-Hartman, 1995, p. 353). When readers do refocus, or engage in problem solving, these activities should be reflected in slower reading times. Consistent with this assumption, several lines of research indicate that sentences are read more slowly in conditions in which the resonance process might initially fail. O'Brien, Plewes, and Albrecht (1990) found that sentences containing anaphoric references were read more slowly when a backgrounded antecedent had been mentioned less often. Reading time is also slower when there are two potential antecedent candidates distinguished only by adjective modifiers (Corbett, 1984; Mason, 1997). Sentences containing contradictions of earlier statements are read more slowly than those without contradictions (Albrecht & Myers, 1995; Albrecht & O'Brien, 1993; Myers, O'Brien, et al., 1994). The pattern-matching access process that is our primary focus is not sufficient to account for every aspect of comprehension. Our intuition suggests that the contents of working memory are continuously evaluated; slow reading times in the face of processing difficulties support that intuition. A complete theory of comprehension would describe the inferential machinery involved in that evaluation process. Nevertheless, we believe that understanding the process by which information in memory is accessed takes priority. There are several reasons for this. First, and most important, that process is basic in the sense that it makes available those memory elements needed for the reader to build a coherent discourse representation. Second, the results of standard memory experiments provide a rich source of hypotheses about the variables that should influence the process of accessing the representation. Third, the models that have been developed to account for performances in standard memory tasks suggest concepts and mechanisms that may underlie memory-based text processing. In view of these considerations, our research has focused on those variables that affect access to the discourse representation. The results of manipulating these variables guide our assumptions about this process. In what follows, we review those results,
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relating them to our assumptions about the process. Following that, we present explicit assumptions about the discourse representation and the process that operates on it, and we describe the results of simulations of the hypothesized process.
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RELEVANT EXPERIMENTAL FINDINGS
Anaphor Resolution
One aspect of the comprehension process that has been extensively studied is the resolution of anaphors (for a review, see Sanford & Garrod, 1989). Because complete comprehension of an anaphor or anaphoric phrase requires the reader to recover specific antecedent information, it is possible to examine those factors that influence the activation of backgrounded concepts by monitoring changes in the availability of antecedent information following an anaphor (e.g., Dell et al., 1983; McKoon & Ratcliff, 1980; O'Brien et al., 1986; O'Brien et al., 1990). Therefore, it is an excellent vehicle for testing the resonance model. The memory-based text processing view and the resonance model suggest several factors that influence the accessibility of the antecedent of an anaphoric reference. Some of these factors are the degree of featural overlap between the anaphor and the antecedent, the extent to which the text has elaborated on the antecedent, the presence of other potential antecedents (or distractors) in the representation, the referential distance between the anaphor and the antecedent, and general world knowledge. In the following brief review, we consider results that indicate that each of these factors influences the reactivation of antecedent information. Following our summary of those results, we also comment briefly on the time course of the resonance process. Featural overlap. The basic process in the resonance model is pattern matching; activation of a concept in the discourse representation depends on the degree of overlap between its conceptual features and those of the concepts in the focal sentence. This accounts for Garrod and Sanford's (1982) finding that pronouns can generally be used only when antecedent information is already active in memory. This is because pronouns carry little semantic content, sharing few features in common with information in long-term memory. In contrast, explicit anaphors (e.g., definite descriptions) carry more semantic content than pronouns, which results in a higher degree of featural overlap between an anaphor and its antecedent. As a result, explicit anaphors can be used to refer to backgrounded antecedents (i.e., antecedents that are no longer active in memory). Consistent with this view, Greene, McKoon, and Ratcliff (1992) found that explicit anaphors are resolved more quickly and easily than less explicit pronominal
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anaphors. Therefore, we limit our discussion of antecedent reactivation to only those instances in which the antecedent has been backgrounded. There is considerable evidence that backgrounded antecedents are reactivated in response to an explicit anaphor (e.g., Dell et al., 1983; McKoon & Ratcliff, 1980; O'Brien, 1987; O'Brien et al., 1986; O'Brien, Raney, Albrecht, & Rayner, 1997) and that the degree of featural overlap between an anaphor and its antecedent governs the speed with which an antecedent is reactivated. For example, McKoon and Ratcliff (1980; see also Dell et al., 1983) found that the time to reactivate an antecedent (e.g., burglar) was faster when the anaphor was a direct repetition of the antecedent than when it was a synonym (e.g., criminal). Presumably, repeating the noun provided greater featural overlap than the synonym. Similarly, Duffy and Rayner (1990; see also Garrod & Sanford, 1981) found that the time to resolve category name anaphors (e.g., bird) was longer when the antecedent was a low typical member of the category (e.g., goose) than when it was a high typical member (e.g., robin). Again, low typical members share fewer features in common with the category than do high typical members (e.g., Rosch, Mervis, Gray, Johnsen, & Boyes-Braem, 1976). Elaboration of antecedents. Frequently, when a passage is examined, we find that there are regions in which propositions focus on some concept; the propositions are related through argument overlap, and they explicitly or implicitly reference the concept. Consider the following excerpt from a passage used by O'Brien et al. (1990): Sally decided to play in the barn. It took all of her energy to push open its great big red doors to get inside. When she did, she climbed up into its loft. She spent the next few hours jumping into the hay. She could see a sparrow had built a nest in one of the barn's rafters. The barn, and Sally's activities in it, are the focus of five sentences. In contrast, consider the following excerpt from the same passage: After breakfast was over, Sally's entire family got in the car and went to church. They spent the entire morning working with all their neighbors painting it and cleaning up the area. Because there are more propositions referring to the barn than to the church, O'Brien et al. referred to the barn as more elaborated. They found that anaphoric references to more elaborated concepts were read more quickly and probes of the more elaborated concept were responded to more quickly. This was true even when the elaborated antecedent was further from the anaphoric reference than the
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unelaborated antecedent was. There are several possible reasons why elaboration may increase accessibility. It not only increases the probability that specific information has been encoded but also increases the number of routes by which a signal from the information being processed can reach the concept. The same mechanisms may account for the finding that propositions that enter into more causal connections are better remembered (Trabasso & Sperry, 1985; Trabasso & van den Broek, 1985) and more quickly retrieved (O'Brien & Myers, 1987; see also Bloom, Fletcher, van den Broek, Reitz, & Shapiro, 1990; van den Broek, 1990). Elaboration need not involve the addition of many sentences to be effective. Albrecht and Myers (1998/this issue) had passages that mentioned an object, such as a desk, either modified by an adjective ("The captain sat at his large desk") or not ("The captain sat at his desk"). Later reference to the desk provided faster access to the episode in which it had been first mentioned when the initial mention had been modified by the adjective. Albrecht and Myers accounted for this finding by hypothesizing that a sentence such as "The captain sat at his large desk" provided access to a desk in the representation by way of either of two propositions: or . Without the adjective modifier, there was only one proposition providing access. Effects of distractors. The presence of more than one potential antecedent will affect the resonance process, resulting in slower retrieval of the correct antecedent. This occurs because the signal from the anaphor is divided among concepts in the discourse representation that share features with it. Corbett (1984) used passages in which a categorical anaphor was modified by an adjective, for example, the frozen vegetable. The preceding text mentioned either one or two members of the category, for example, frozen peas and fresh carrots. Time to read the adjective-noun anaphor was significantly slower when the distractor (fresh carrots) was present. Mason (1997), using eye movement methodology, replicated this result. Both the gaze duration data and naming time probes in a subsequent experiment indicated that activation immediately followed the eye's encounter with the anaphor, a result consistent with the fast resonance process we have hypothesized. Further evidence that resonance is reduced when the signal encounters two discourse elements that are closely related to the contents of working memory may be found in an experiment by Albrecht and Myers (1998/this issue). Their passages contained a goal-setting episode, followed by a second, unrelated, episode. Later mention of an object (e.g., desk) that was present only in the first episode served as an effective reminder of that episode. However, if the object had been associated with both episodes in the passage, the effectiveness of that cue in reactivating the first goal-setting episode was reduced. Associating a contextual cue with more than one episode apparently created a fan effect that reduced the level of the signal reaching the targeted episode (Myers, O'Brien, Balota, & Toyofuku, 1984; Reder & Anderson, 1980; Reder & Ross, 1983).
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O'Brien and his colleagues (O'Brien, Albrecht, Hakala, & Rizzella, 1995; O'Brien et al., 1990) provided further evidence that all antecedents that share features in common with an anaphor will initially be reactivated in response to that anaphor. O'Brien et al. (1990) found that reinstatement of a distant antecedent also resulted in the reactivation of a potential antecedent that had features in common with both the anaphor and the correct antecedent. In a subsequent study, O'Brien et al. (1995) showed that, once reactivated, potential antecedents that are not selected are suppressed. Lucas, Tanenhaus, and Carlson (1990) also reported evidence that distractors are suppressed. Gernsbacher (1989) and MacDonald and McWhinney (1990) reported similar results with pronominal anaphors. Referential distance. The distance between an anaphor and the referenced antecedent also influences the accessibility of the antecedent (e.g., Clark & Sengul, 1979; Duffy & Rayner, 1990; Ehrlich & Rayner, 1983); antecedents that are more physically distant require more time to be resolved. However, in many of these studies, the near antecedent appeared in the same sentence as the anaphor, whereas the distant antecedent appeared one or more sentences back. Thus, the distance effect is often the result of the near antecedent being active in memory when the anaphor is encountered (i.e., in focus) and the distant antecedent requiring reactivation (for an excellent discussion of the role of focus in anaphor resolution, see Garrod, Freudenthal, & Boyle, 1994). In order to more directly examine the role of referential distance in the reactivation of antecedent information, both the near and distant antecedent must be backgrounded (i.e., no longer in focus) when the anaphoric expression is encountered. O'Brien (1987; O'Brien et al., 1995; O'Brien et al., 1990) found that, when two potential antecedents were backgrounded, the more distant antecedent required more time to be reactivated. One possible explanation is that resonance is a function of a concept's strength, and that strength decays over time, making it more difficult to retrieve more distant antecedent information. An alternative explanation, consistent with the current instantiation of the resonance model, rests on the assumption that more recently presented concepts and propositions are more likely to overlap with the current contents of working memory. Another way of saying this is that more recently presented information, even if no longer in working memory, is more likely to be relevant to (share concepts with) what is currently being read. If this assumption is correct, these propositions and concepts will resonate more than will more distant propositions and concepts. This explanation has added implications: The advantage of proximity should be reduced when the distant antecedent has received greater elaboration, or has more features in common with the anaphor, or is in propositions that share more arguments with the propositions in working memory. Of course, it also follows that there may be passages for which no distance effects are observed, either because the elaboration of a distant antecedent cancels the advantage due to proximity of a near one
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(e.g., O'Brien et al., 1995; O'Brien et al., 1990), or because factors such as featural and argument overlap and elaboration are equated. In this respect, it is interesting to note that O'Brien and Myers (1987; see also Lutz & Radvansky, 1997) found no effect of distance on recall of antecedents. Resonance of world knowledge. One assumption of the resonance model is that, as each concept is encoded, it sends a signal to all of memory in parallel, including general world knowledge. Resonance is not restricted to concepts contained in the episodic representation of the discourse; concepts that have semantic features in common with an anaphor will resonate whether or not they were present in the discourse. Furthermore, propositions stored in the reader's knowledge base that share arguments with text propositions will also resonate. In general, it should be the case that resonating concepts should be dominated by those in the episodic memory trace, and they should resonate to a higher degree than concepts that are semantically related but are not part of the episodic representation. Thus, readers should experience little difficulty discriminating between concepts that appeared in the discourse and those that did not. However, if there is sufficient activation of a concept that did not appear in the passage, readers may mistake it as information that was part of the explicitly stated text. O'Brien and Albrecht (1991) found that reactivation of a target antecedent was accompanied by activation of a potential antecedent that was strongly suggested by the context but had not appeared in the passage. In a subsequent experiment, they found that readers often selected and incorporated the contextually related but incorrect concept as the correct antecedent, despite the fact that it had never occurred in the passage.
The Time Course of Access An important characteristic of the memory-based view of anaphoric processing is that recovery of antecedent information can begin prior to complete processing of an anaphoric phrase. This contrasts with various forms of a search-inference model, in which reactivation of an antecedent phrase is initiated only after the entire anaphoric phrase has been encoded. As an example of the present view, consider an anaphoric phrase made up of an adjective and a head noun (e.g., the warm beer); we assume that the adjective sends a signal to memory as soon as it is encoded. If that adjective (or a conceptually similar adjective) is also present in a targeted antecedent phrase, and the signal from the adjective is sufficiently strong, it may activate the entire antecedent phrase before the head noun of the anaphoric phrase has been encoded. Monitoring eye movements, O'Brien et al. (1997) found that the signal from an adjective modifier was sufficient to reactivate an entire antecedent phrase. However, when the distance between the anaphoric phrase and the antecedent was increased, reactivation of the antecedent phrase did not occur until the entire anaphoric phrase had been read. Presumably, as
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the distance between the anaphor and its antecedent increased, the signal from the entire anaphoric phrase was necessary to produce a signal strong enough to activate the antecedent.
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Reactivation With Locally Coherent Text Evidence of reactivation of antecedent information in response to reading an anaphoric phrase provides strong support for the memory-based text processing view and the resonance model's explanation of how backgrounded antecedents are reactivated. However, unresolved anaphors constitute a local coherence break, and virtually every model of discourse comprehension would predict that this would trigger a search of long-term memory in an attempt to reestablish coherence. A critical aspect of the resonance model is that this reactivation of information from inactive elements in the discourse representation is passive and continuous. Important evidence of the passive aspect of the resonance process would be a demonstration that comprehension is sensitive to global coherence as well. That is, it is important to demonstrate that inactive elements in the discourse representation become active and are evaluated even when a text is locally coherent and searches of long-term memory are therefore not necessary. One such demonstration was provided by O'Brien and Albrecht (1992). They presented individuals with passages in which an initial sentence placed a protagonist in a particular location (e.g., "Kim stood inside/outside the health club"). A later sentence moved the protagonist from the original location (e.g., "She decided to go outside the health club"). When Kim was originally placed outside the health club, the second location sentence was contradictory. In one condition, the contradictory location sentence was separated by several sentences from the first location sentence; it was always locally coherent but resulted in a contradiction if readers had access to the earlier, now backgrounded, location sentence. Despite the fact that the second location sentence was locally coherent, reading times indicated that readers noticed the contradiction. Readers had access to global information even when the text was locally coherent. Additional evidence for this conclusion, using very different passages and responses to recognition probes, was provided by Greene, Gerrig, McKoon, and Ratcliff (1994; see also Lea, Mason, Albrecht, Birch, & Myers, 1998; McKoon et al., 1996). Reinstating a character into the text reactivated another character associated with her in the earlier backgrounded introduction to the text. Again, this occurred even though the text was locally coherent at the point at which the reinstatement occurred. In several series of experiments, we (Albrecht & Myers, 1995; Albrecht & O'Brien, 1993; Hakala & O'Brien, 1995; Huitema, Dopkins, Klin, & Myers, 1993; Myers, O'Brien, et al., 1994) provided further evidence that the resonance process activated relevant backgrounded information even when local coherence had been maintained. Each passage began with the introduction of a protagonist followed by an elaboration of some characteristic of the protagonist (e.g., "Mary was a strict vegetarian"). Following this, there was a shift in topic back to the
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story line in the introduction. The protagonist remained in focus but there was no further mention of the elaborated characteristic until the target sentence appeared several sentences later. In the target sentence, the protagonist was described as engaging in some action that was consistent, inconsistent, or neutral with respect to the earlier elaboration (e.g., "Mary ordered a cheeseburger and fries"). Despite the fact that the elaborated characteristic was not active in memory immediately prior to the target sentence (Myers, O'Brien, et al., 1994), reading times on the critical sentences were significantly longer in the inconsistent condition than in either the consistent or neutral conditions. Again, readers experienced comprehension difficulty in a condition in which local coherence was maintained but global coherence was not. Consistent with the assumptions of the resonance model, when the reader encoded the sentence indicating that Mary ordered a cheeseburger and fries, that information sent a signal to all of memory. All memory traces relevant to Mary's eating habits resonated in response to that signal. When information indicating that Mary was a vegetarian was reactivated by this process, a global coherence break occurred. This, in turn, resulted in a slowdown in reading as the reader attempted to reestablish coherence. Although we have interpreted these results as reflecting the operation of a passive bottom-up process, they are also consistent with a constructionist position (e.g., Graesser, Singer, & Trabasso, 1994) that holds that the reader attempts to construct a coherent global model of the situation. Within such a framework, it could be argued that inconsistencies will be noted. However, without additional ad hoc assumptions, the constructionist position would appear unable to account for processing difficulties due to information that has been backgrounded when the text is both locally and globally coherent. Consider a passage in which the following sentence appeared in an early part of the text (O'Brien, Rizzella, Albrecht, & Halleran, 1998): "Mary recalled that she had been a health nut and a strict vegetarian for about ten years but she wasn't anymore." After six sentences in which the topic was changed, the reader encountered the target sentence: "Mary ordered a cheeseburger and fries." This sentence is both locally and globally coherent, and therefore, from a constructionist standpoint, readers should not have experienced comprehension difficulty. However, because the resonance model is not sensitive to tense or the intended meaning of backgrounded information, it predicts that the information in the elaboration region should continue to be reactivated, causing comprehension difficulty as the reader attempts to integrate that information with the target sentence. Consistent with the resonance model, O'Brien et al. found a significant disruption in reading times for the target sentence when the text was modified so that the critical characteristic was presented as having never been true. In a subsequent study, Cook, Halleran, and O'Brien (1998/this issue) rewrote the passages so that the critical characteristic was attributed to someone other than the protagonist (e.g., "Joan was a vegetarian . . ."). This change eliminated the comprehension difficulty readers were experiencing with the target sentence
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("Mary ordered a cheeseburger and fries"). However, probe times revealed that the critical information continued to be reactivated even though its content was not relevant to understanding the target sentence. Presumably, that information was reactivated because it shared features with information in the target sentence; however, because the content of the reactivated information was not relevant to the content of the target sentence, further processing of that sentence was not affected. A similar pattern emerges when we examine factors that govern the availability of backgrounded causal or goal-based information; initial activation of such information appears to be independent of whether it is necessary or relevant to the integration process. For example, Rizzella and O'Brien (1996) found that, when readers encountered causal consequences with a readily available and sufficient causal antecedent, distant causal antecedents that were highly elaborated were also reactivated/This occurred even though the causal consequence had already been provided with a sufficient causal antecedent, and therefore, reactivation of the distant cause was unnecessary to maintain causal coherence. This is exactly what a dumb activation process would lead us to expect; although the earlier causal information is not needed for comprehension, it is reactivated. In order for a model that emphasizes the search for causal coherence (e.g., Graesser et al., 1994; van den Broek, 1990) to account for this result, it must assume that the reader is not satisfied to find a near-sufficient cause but continually searches the representation for all possible causes. Such a process would be inefficient, engaging the reader in continually exhaustively searching a text representation that grows larger with each new sentence that is read. Albrecht and Myers (1995) provided evidence that such an exhaustive search does not occur. They found that reactivation of an unsatisfied goal of a protagonist occurred only when the text currently in focus contained information associated with the backgrounded goal. If the protagonist was sitting at a large desk when the goal was first mentioned, reinstating that object in the text was sufficient to reactivate the goal. In the absence of this reinstatement of context, readers exhibited no comprehension difficulty when reading an action that did not satisfy the backgrounded goal. If readers continually monitored goal-based information, then the reinstatement of the earlier context should have been unnecessary to reactivate the unsatisfied goal. In summary, the findings of Rizzella and O'Brien (1996) and Albrecht and Myers (1995) are compatible with the memory-based text processing position. They appear to pose problems for models that emphasize a "search (or effort) after meaning" (Graesser et al., 1994, p. 371). If such a search is exhaustive, it may account for the Rizzella and O'Brien findings, but it should also have found the global inconsistency in the Albrecht and Myers passage, even in the absence of a contextual cue. On the other hand, if the search terminates when a sufficient cause is found, the model fails to account for the Rizzella and O'Brien results. Our findings concerning the factors that govern the availability of causal- and goal-based information, as well as the availability of global information in general,
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provide strong support for the basic assumption of the memory-based text processing view and the resonance model. Higher order processes in which readers may attempt to actively maintain global coherence, monitor goal-based information, or maintain causal coherence do not affect the initial reactivation process; instead, they are applied to the results of the reactivation process when the reader attempts to integrate that reactivated information with what is currently active in memory.
A SIMULATION MODEL OF THE ACCESS PROCESS
The experiments reviewed in the preceding section demonstrate that, during the course of reading a text, concepts and propositions embedded in the text fluctuate in their accessibility. In many instances, the information becomes only momentarily reactivated; because it fulfills no function in the comprehension of the focal sentence, it may be suppressed, or at least supplanted, by other information in a limited-capacity working memory. In other instances, the reactivation of information read earlier often provides the basis for comprehending the focal sentence; as in many of the studies we cited, distant information may provide the antecedent for an anaphor in a sentence currently being read or the cause of some otherwise anomalous action in the focal sentence. In this way, the activation process provides a basis for global coherence, for relating pieces of information that may not only be separated by physical distance but also, as in many of our experiments, by intervening episodes. A minimal requirement of a model of activation is that the outcomes of simulations mimic the changes in accessibility reflected in the data. In evaluating the results of simulations, we assumed that this requirement was met if targeted concepts and propositions were absent from working memory when both text analysis and experimental results indicated that they were backgrounded and if they were present in working memory when our data indicated that they were active. Ideally, the ability to meet this requirement should not depend on one particular point in a parameter space, and the parameter values that adequately account for effects of interest should do so for several different passages used in different experiments. The model should also provide a framework for incorporating the factors that have been found to influence accessibility. In our initial attempts to model the fluctuation in accessibility of information, we simulated Kintsch's (1988) C-I model with the added assumption that the construction process included elements from the long-term memory representation of the text as well as from the reader's world knowledge. This appears to be consistent with the more recent statement by Ericsson and Kintsch (1995). We also used the Kintsch-Welsch (Kintsch & Welsch, 1991) algorithm for modifying the strengths of nodes and links. A problem we encountered was that propositions from highly elaborated portions of the text were in working memory when analyses of the texts and our data indicated that they should be backgrounded. We considered
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other algorithms for changing the strengths of connections within the C-I framework, introducing several parameters in doing so; we continued to encounter difficulties in backgrounding and reactivating information in a manner consistent with our experimental results. This does not mean that some further modification of the C-I model would not be more successful. However, we note that Goldman and Varma (1995) reported that one such modification, their Collaborative Activation-Based Production System-Construction-Integration (CAPS-CI) model, has a problem similar to the one we noted: Interconnected sets of propositions accrued greater amounts of activation and remained in the buffer, making it difficult for new inputs to become highly active. In view of these considerations, we decided to investigate other algorithms for accessing information in the text representation. The simulation model we present is also sensitive to interconnections among propositions but, as we shall see, not overly so. It backgrounds and reactivates information in much the way our participants do. We have simulated several versions of the resonance model that vary in complexity, incorporating different numbers of processes and parameters. In what follows, we present only the simplest version of these simulation models, and we present applications to only a few of the results we view as most basic. Our goal at this point has been to determine whether a relatively simple bottom-up model can account for at least the basic effects we have summarized in the preceding sections. Presumably, as we extend the range of applications to other effects and measures, and as we attempt to provide a quantitative fit to data, we will be forced to consider more complex processes and structures. The Resonance Model The representation. As in the Search of Associative Memory (SAM) model (Gillund & Shiffrin, 1984; Raaijmakers & Shiffrin, 1980, 1981), we view the memory representation as a retrieval structure consisting of images, collections of conceptual and perceptual features, and interitem information. The primary difference between episodic and knowledge-based images is that the former also contain information about the experimental context and text information such as the theme of the passage. The elements of the text representation are propositions and concepts (Bovair & Kieras, 1985; Turner & Greene, 1978) as well as sentence markers; these last are essentially local context markers, as in several memory models.1 We assume certain rules of communication between memory elements: 1. Signals pass directly between the sentence marker and elements representing propositions within that sentence; 1 Although we view the sentence marker as a contextual element, or a set of elements contained in the images of propositions, it has been convenient in our simulations to treat it as a single element that can signal to the propositions within the relevant sentence.
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2. Signals pass between propositions and concepts embedded in them; and 3. Signals pass between two propositions when one member of the pair is embedded in the other or when all arguments are identical.
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Figure 1 illustrates these lines of communication for one sentence (Sentence 3; S3) of a passage from Albrecht and Myers (1995). In the top panel, propositions are "linked" to the marker denoting the sentence in which they are embedded, consistent with Rule 1; for example, S3 comprises Propositions 10 through 13 and essentially states that the captain must do the ship's inventory before he can
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