A critique of schema-based theories of human story memory

Poetics 9 (1980) 23-49 0 North-Holland Publishing Company

A CRITIQUE OF SCHEMA-BASED THEORIES OF HUMAN STORY MEMORY

PERRY W. THORNDYKE

and FRANK R. YEKOVICH

The concept of a ‘schema’ as a theoretical construct has regained prominence among memory researchers, particularly those studying prose learning. A schema is a cluster of knowledge that describes the typical properties of the concept it represents. Recent theories built upon the notion of schemata have explained numerous results in human comprehension, recall, and summarization of prose. While schema theory provides a plausible and descriptive framework for understanding human knowledge processing, it is ill-constrained and provides few detailed pro_ cess assumptions. This lack of constraint allows sufficient flexibility to accommodate post hoc many empirical results. However, because of this flexibility, the theory is of limited predictive value and is not testable as a scientific theory in its current form. We detail the strengths and weaknesses of schema theory, affirm its promise as a theory of human memory, and suggest areas for future theoretical development.

Introduction During the past five years a growing body of research has examined how people process, comprehend, and remember information in texts. This research has had two complementary objectives. First, the study of discourse processing has provided psychologists a medium in which to develop general yet comprehensive theories about human memory. These theories have drawn heavily from concepts in both artificial intelligence and linguistics. Second, text learning provides a domain for the study of language structure and processing that, while extremely complex, is a typical and important area of cognitive activity. Traditionally, the study of text structure was left to linguists and rhetoricians (e.g., Rockas 1964), while psychologists investigated memory for words and isolated sentences. However, the recent emergence of ‘cognitive science’ has resulted in the melding of these various disciplines and the development of new research paradigms. One concept resurrected as a result of this synthesis is the notion of memory schemata (Bartlett 1932). As it is geneially interpreted today, a memory schema is a structured cluster of knowledge that represents a particular concept (Minsky 1975; Winograd 1975; Bobrow and Norman 1975; Rumelhart and Ortony 1977). This cluster comprises a set of concepts and associations that describe the properties of the concept in question. Schemata represent the underlying knowledge for 23

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such complex and disparate concepts as objects, percepts, events, sequences of events, and social situations. For example, consider the concept of a birthday party. When people think of a birthday party, their thoughts typically include a person whose birthday it is, other partygoers, presents, cake, ice cream, decorations, party favors, and events that relate tham all. This general ‘birthday party’ knowledge may be represented by a BIRTHDAY PARTY schema that details the concepts and events that occur in this larger event. Thus, a schema provides a parsimonious description of the stereotypical case of the complex concept it represents. Several researchers have begun to study memory schemata in the context of human text processing (Kintsch and van Dijk 1975, 1978; Rumelhart 1975,1977; Kint sch 1977 ; Mandler and Johnson 1977 ; Thorndyke 1977,1978 ; Rumelhart and Ortony 1977; Anderson 1978; Mandler 1978; Stein and Glenn 1978; Thorndyke and Hayes-Roth 1979). Essentially, this work has attempted to model the underlying memorial structures that encode prose passages, In particular, these researchers have developed the hypothesis that readers use previously-leaned schemata to aid comprehension and encoding of simple narrative stories in memory. As a consequence of this point of view, schemata have acquired a special status as a theoretical construct in cognitive psychology, and the results of numerous experimental studies have been interpreted within this theoretical framework. The purpose of the present paper is to critically evaluate the adequacy of schema theory as a psychological model of memory. In so doing we review much of the research that has contributed to the rise in popularity of this theoretical framework. We argue that while schema theory provides a convenient framework for understanding human knowledge processing, it has not as yet been submitted to the type of rigorous empirical evaluation required of scientific (and most psychological) theories. We do not contend that the assumptions entailed by schema theory are wrong. Indeed, we have adopted the tenets of schema theory in our own research (Thorndyke 1976, 1977, 1978,1979; Yekovich and Thorndyke 1980). Rather, we hope to stimulate future research by pointing to assumptions that are widely accepted but remain empirically unsupported. The remainder of this paper is organized as follows. First, we outline briefly the historical development of the schema as a theoretical construct in psychology. Next, we attempt to synthesize the current state of development of schema theory by identifying the common properties of the variants (e.g., Kintsch and van Dijk, 1978; Rumelhart and Ortony 1977; Thorndyke 1977; Bobrow and Norman 1975; Schank and Abelson 1977). Third, we present a set of generalities about human text memory derived from available empirical evidence. We then demonstrate how the composite schema theory can account for these data. The next section critically evaluates the adequacy of this theoretical framework against criteria of hypothesis testing normally employed in empirical sciences. Finally, we raise some unresolved issues in schema theory and suggest directions for future research.

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A short history of schema theory

As an explanatory concept, the schema has been operative in psychology for well over fifty years. The term ‘schema’ itself dates at least from Kant (1787), who developed the idea that people’s experiences are collected together in memory and that these collections are defined by common elements. Since these common elements identify categories of experiences, they permit the synthesis of abstract knowledge that represents the category. This higherorder concept can be understood without reference to any particular occurrence within the category. In addition, one identifies experiences of the category by referring to the general schema that describes the category. This view of schemata was adopted by the neurologist Head (1920), who stated that anything entering consciousness is “charged with its relation to something that has gone before”. In a similar vein, Woodworth (1938), in the classic text on experimental psychology, remarked that the process of remembering involved the “revival of one’s own experiences”. The schema concept rapidly spread to many branches of psychology and took on similar but slightly different meanings in each. Gestalt psychologists found the concept of abstract schemata useful in describing memory for perceptual information (e.g., Woodworth 1938). Piaget’s (1926) early work with children used schemata to describe the creation and developmental change in cognitive structures. Researchers in problem solving (e.g., Selz 1913, 1922; Flach 1925; Betz 1932) viewed schemata as solution methods or plans of operations guiding the problem solver’s behavior. The latter variant on schemata is most similar to that adopted by Bartlett (1932), the acknowledged originator of the use of schemata to describe story recall. Bartlett assumed that abstract knowledge structures aided recall of past events. His War of the Ghosts experiments demonstrated that prose recall involved reconsrmcrive as well as repmducriue memory processes. Bartlett’s subjects consistently produced idiosyncratic elaborations in addition to some of the original facts in the story. Bartlett interpreted these data as evidence that subjects reconstruct the events of a story using a few details and an abstract cognitive schema as an elaboration plan. The recent revival of schemata as theoretical constructs has its roots in two lines of research. The first area is artificial intelligence, where researchers have been developing representations for knowledge of complex situations, events, and concepts. The data structures that have emerged consistently utilize knowledge clusters that represent typical cases of the concepts they represent. This research is fypified by notions such as ‘frames’ (Minsky 1975; Kuipers 1975;Wmograd 1975), ‘scripts’ &hank and Abelson 1975, 1977), or other forms of schemata (Schmidt 1976; Moore and Newell 1974). The second domain of research in which memory schemata have recently appeared is in psychological studies of memory for prose. Principally inspired by the work of Bartlett, researchers have begun to extend and formalize his ideas by

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modeling the knowledge structures underlying memory for story information (Rumelhart 1975, 1977; Rumelhart and Ortony 1977; Kintsch and van Dijk 1975, 1978; Thorndyke 1977, 1978; Mandler and Johnson 1977; Mandler 1978; Stein and Glenn 1978). This research has focused on demonstrating that text comprehension, encoding, and memory retrieval rely heavily on the activation and use of well-learned memory schemata. These schemata encode knowledge of how events are structured, how event sequences combine and form episodes, and how entire stories are constructed from sequences of episodes. Within this general framework, several variations in the details of schema structures have been proposed. However, all variants share several common assumptions about the structure of memory schemata. We turn now to a consideration of the modern notion of schemata.

Current formulations of schema theory Because the concept of schemata as organizers of human experiences is so general, it is perhaps inevitable that each particular formulation of schemata should differ from all others in some details. As in the early research on schemata, each researcher has proposed a model that differs from the others in precisely what a schema is, how it is structured, or how it is used. In this section we attempt to synthesize a composite description of schemata as derived from recent research. In part, exact formulations of schema theory have been influenced by the class of memory processes under consideration. One major group of models has focused on input processes associated with the use of schemata. These models address (a) how memory schemata are activated and used to guide to organization of incoming information, and (b) how that information is represented in memory. Essentially, these comprehension+riented models show how schemata contain the knowledge necessary to interpret and encode complex world events (e.g., Minsky 1975; Schmidt 1976; Stein and Nezworski 1978; Rumelhart and Ortony 1977; Thorndyke and Hayes-Roth 1979; Schank and Abelson 1977). A related approach has emphasized the importance of people’s ‘perspective’ in comprehension, and has demonstrated that frequently a single text permits different interpretations based on alternative schemata (Anderson 1977, 1978; Anderson er al. 1977; Pichert and Anderson 1977 ; Bower 1978). A second category of schema models has focused on output functions associated with the use of schemata. These models describe how schemata influence recall of information from memory (Mandler and Johnson 1977; Rumelhart 1975; Thorndyke 1977,1978; Kintsch and Greene 1978; Mandler 1978; Bower et al. 1979) and summarization of texts from memory (Rumelhart 1975, 1977; Thomdyke 1977, 1978; Kintsch er al. 1977; Kintsch and Greene 1978). Admittedly, these categorizations are somewhat arbitrary and incomplete. Indeed, a few models have attempted more general and comprehensive formulations of memory schemata (Bobrow and Norman 1975; Rumelhart and Ortony 1977;

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Winograd 1977; Kintsch and van Dijk 1978). Nevertheless, these categories do reflect the two primary types of memory phenomena addressed by most schema theorists. In spite of differing orientations, several common assumptions underlie the various formulations of schema theory. These commonalities include five putative properties of schemata: concept abstraction, hierarchical organization, instantiation, prediction, and induction. A brief discussion of each property follows. Concept abstraction

A schema represents a prototypical abstraction of the concept it represents. This abstraction encodes the constituent properties that define a typical instance of its referent. In some models, this structure is represented by a ‘grammar’ that specifies both the concepts within the schema and the rules for combining them (Rumelhart 1975, 1977; Mandler and Johnson 1977; Thorndyke 1977; Stein and Glenn 1978). In other models, the structure is represented as a network of related properties or event sequences (Rumelhart and Ortony 1977; Schank and Abelson 1977). The constituent properties may consist of perceptual features, semantic primitives, states or events in the world, or other schemata. Hierarchical organization

Schemata are organized into a generalization hierarchy in memory. The hierarchy relates concepts of different degrees of specificity. For example, the schema for a birthday party presumably specifies and elaborates a more general PARTY schema. While both have many of the same properties, the properties of the birthday party are more precisely determined than for the generic party. A party might have ‘food’ as one of its properties, while a birthday party schema would specify ‘cake and ice cream’ as the typical foods. Thus, changing the level in the generalization hierarchy changes the constraints on the constituent properties. Another type of hierarchical organization arises when a schema is defined by a combination of constituent elements. For example, an episode schema might consist of a protagonist, a goal, an attempt by the protagonist to achieve the goal, and an outcome of the attempt. The attempt to achieve the goal might itself be another episode, thus producing a recursive embedding of an episode within another. In general, the characterization of story grammars as schemata has assumed such hierarchical organizations of story constituents (Rumelhart 1975, 1977; Mandler and Johnson 1977 ; Thomdyke 1977; Stein and Glenn 1978). Instantiation

The properties that characterize a schema are represented as variables, or slots, that can be tilled whenever the schema is used to organize incoming information.

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The process of matching input to slots in the schema is called instantiation of the schema. Such instantiation is similar to the creation of a ‘token’ node in semantic network models (e.g., Anderson and Bower 1973) to represent the specific occurrence of a general concept. When a schema is instantiated during comprehension, a copy of the general schema is created with data from the input stream filling the variable slots. This process of instantiation permits the organization and encoding of incoming information into a familiar, coherent, conceptual representation. Returning to the BIRTHDAY PARTY example, suppose we are told: “John’s birthday party was a success. He appreciated both the angel food cake and the new sweater”. Using our knowledge of the BIRTHDAY PARTY, we assume that the cake was John’s birthday cake and the sweater was his present. Prediction

As the previous example illustrates, schemata permit reasoning from incomplete information. This reasoning takes the form of expectations about information we expect to obtain to fill the slots in the currently active schema. Such predictions can guide the interpretation of incoming information and support inferential processes that match input to expectations, as in the case of deciding that a sweater was a birthday present. Furthermore, if someone tells us only that they had a birthday party, we may infer that cake was served. That is, default values supplied by the general schema may be substituted in the description of the event when the explicit information supplied in the description is incomplete. Induction

Schemata are formed by induction from numerous previous experiences with various exemplars of the generic concept. Presumably, schemata develop through a process of successive refinement: as we accumulate additional experiences with a concept, our expectations for the expected properties, or slot fillers, of the concept become more clearly defined. For example, consider how our BIRTHDAY PARTY schema develops. Over the years, repeated attendance at birthday parties leads us to develop and modify our knowledge of party formats and traditions. These properties provide a general description of the structure of memory schemata. One may notice, however, that these characteristics assume little about the cognitive processes that control and operate on schemata. For example, it is unclear how schemata are activated, precisely how input is matched to expectations, or how information that violates the schema is encoded. Later we shall consider further the need for more detailed process assumptions. First, however, let us consider how the theory characterized by the properties outlined above can be applied to an analysis of human story memory. Many simple stories share a common organization for the sequence of events occurring in them. Story schemata provide a representation of this common organization occurring in

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many narratives. This organization can be expressed in terms of constraints on the arrangement of situations and events in a well-formed passage. Consider a typical brief story in which a protagonist tries to achieve some goal. The plot sequence in such stories normally involves (a) the introduction of the main character and the problem to be solved, (b) one or more episodes directed at solving the problem, and (c) an eventual resolution of the problem by the protagonist. Further, each episode generally entails the establishment of a subgoal by the protagonist, an attempt to achieve that subgoal, and an outcome of the attempt. These high-level descriptions of typical plot organizations constitute schemata for the story structure, That is, these schemata describe the syntax of narrative organization just as earlier phrase structure grammars defined the syntax of sentences (e.g., Chomsky 1957). Many of the attempts to detail the schematic structure of narratives have in fact specified grammars similar to earlier sentence grammars. These grammars provide a set of rewrite rules for decomposing a story into its constituent structural elements (Rumelhart 1975; Mandler and Johnson 1977; Thorndyke 1977; Stein and Glenn 1978). Each rule may be thought of as a schema for a higher-level element (e.g., an episode) that specifies the set and sequence of constituent elements (e.g., subgoal t attempt t outcome).

Human text memory: empirical evidence Before considering current theories of story schemata in detail, we first review the empirical data obtained from studies of human text learning. Typically, subjects in prose memory experiments first read one or more texts and are then tested. The experimental manipulations generally occur in the texts themselves, or in the tasks that subjects perform during presentation or at test time. The typical task requires some form of memory retrieval, such as recall, recognition, or summarization of the passage content. Subjects’ responses are then scored for content in order to derive quantitative and qualitative indices about memory for the material. In order to represent the content of a text, researchers have used a unit of analysis called the proposition. A proposition has been defined either as a simple, atomic relation between two or more concepts (e.g., Kintsch 1974; Meyer 1975) or as a syntactic clause (e.g., Thomdyke 1977), depending on the analytic detail required by the researcher. Despite this difference researchers have reached a general consensus in their experimental results. Thus, our discussion ignores this subtle distinction in usage. What have psychologists learned from this experimental work? In summarizing the major results from recent prose research, we present several generalities about prose memory that emerge from the data. Our presentation focuses on empirical evidence unadorned by theoretical conjecture. We shall return to schema theory in the next section to provide a theoretical account for the findings described here. When subjects recall a text from memory, they produce only a subset of the

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original information, even when recall immediately follows presentation. This result, first obtained by Bartlett (1932), has since been replicated by many researchers in the field. The striking aspect of subjects’ recall protocols is that some propositions are consistently recalled by nearly all subjects, whereas other propositions are recalled infrequently (Kintsch 1974; Meyer 1975,1977; Thorndyke 1977; Mandler and Johnson 1977). Furthermore, this recall probability is independent of the proposition’s serial position in the passage (Meyer and McConkie 1973). However, the subjective ‘importance’ of a proposition does influence its memorability (Johnson 1970). Johnson had students rate the propositions in a story for their relative importance to the passage meaning. Different subjects who were presented the story for recall tended to remember the same propositions that had been consistently rated as important. Meyer and McConkie (1973) demonstrated the same relationship between a proposition’s rated importance and its memorability. Taken together these results suggest a ‘hierarchy’ of importance for the ideas in a passage (i.e., an implicit structure). Further, this importance tends to be a good predictor of a proposition’s recall. Since these earlier demonstrations of the effect of propositional importance on recall, several researchers have developed formal schemes for representing the structure of prose passages (Frederiksen 1975; Kintsch 1974; Meyer 1975; Thorndyke 1977). According to these theories, the meaning of a text is characterized by an underlying configuration of propositions and relations among those propositions. The representation is a hierarchical structure with propositions connected through associations or relational links. These systems theoretically associate a proposition’s importance with its level in the hierarchy: the higher a proposition is in the hierarchy, the more important it is. Analyses of recall using these formulations have also demonstrated the importance or ‘levels’ effect: a correlation between propositional importance and recall probability. The recall function shown in fig. 1 depicts a typical levels effect obtained in an experiment by Yekovich and Thorndyke (1980): recall decreases with descending level in the representational hierarchy (i.e., with decreasing importance). That is, recall of propositions at Level 1 in the hierarchy is better than recall of propositions at lower levels (i.e., Levels 2 and 3). Propositional importance has also been shown to influence story summarizations (Rumelhart 1975, 1977; Thomdyke 1977). In these experiments subjects read stories and then wrote short abstracts (20-80 words) from memory. The propositions included in the summaries usually corresponded to slight modifications of the toplevel (important) propositions in the story structure. This result held either when the summaries were produced from memory or when subjects could refer to the texts. Additionally, Thorndyke (1977) contrasted the probabilities of propositional recall on a memory test with the probability of including the proposition in the summary, given that it had been recalled. This provided a measure of the degree of overlap of the propositions produced in both protocols. As expected, important propositions occurred consistently in both recalls and summaries. Unimportant propositions were rarely included in summaries even when they had been previously recalled.

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70 -

60 -

8 z E J!

50-

40 -

3Ol 1

2 Level

?3

in hiewchy

Fig. 1. Recall and recognition of propositions from different hierarchical levels in a narrative text (from Yekovich and Thorndyke 1980).

While propositional importance does influence recall probability, it seems tp have little effect on recognition memory. We recently completed a study in which students attempted to recall a presented story and then were given a recognition test (Yekovich and Thorndyke. 1980). The recognition items were story propositions that were either in their original syntactic form (TRUES), paraphrased (PARAPHRASES), or altered in meaning (FALSES). The subjects’ task was to judge whether or not the exact statement had occurred as a part of the text. The propositional recognition and recall results are plotted in fig. 1 as a function of propositional importance. The graph depicts three important findings. First, the probability of recognizing a TRUE proposition did not vary as a function of importance, as shown by the top line in fig. 1. Second, there was little correspondence between recognition of TRUES and recall of these propositions on the recall test. In fact, an overall correlation between item recognition and item recall showed virtually no relation between the two (r = 0.04). Finally, subjects were more likely to correctly reject a paraphrase of an original proposition if it was unimportant than if it was important. That is, the more important a proposition was, the less sensitive subjects were to its precise wording. Thus far, our discussion has focussed on propositional importance and its rela-

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tion to story memory. Another area of research has investigated the influence of the causal and temporal relations among events on the comprehensibility and memorability of texts. We turn now to a summary of those findings. A coherent story differs from a set of isolated sentences in that it has a unifying context, a recognizable temporal sequence of events, and a fixed set of actors or topics. A typical story presents events in an orderly manner, supplying (either explicitly of implicitly) motivations for the characters, causes and consequences of the events, and cues to the temporal sequence in which the events occur. The extent to which these conventions are preserved in a text determines how comprehensible the text is. In general, the more explicit the temporal, causal, and intentional relationships among events in a story, the more comprehensible the story is. Furthermore, the comprehensibility of a text is a good predictor of its memorability. Thorndyke (1977) found that subjects’ ratings of story comprehensibility was highly correlated with the percentage of the story they could recall. On both comprehension and recall, subjects’ performance decreased as a function of increased distortion from the coherent form of the passage. This relationship between coherence and memorability has been found by many investigators (Kintsch 1977; Stein and Nezworski 1978; Mandler 1978; Stein and Glenn 1978). In addition, obscuring these causal and temporal relations leads to predictable distortions in recall. Subjects presented with poorly-structured stories are likely to produce in recall elaborations consistent with a more normal story line (Rumelhart 1977; Mandler 1978; Stein and Glenn 1978; Thorndyke 1977; Kintsch and Greene 1978; Spiro 1977). In fact, even when instructed to recall a story verbatim, they often are unable to remember the exact original event sequence when it deviates from the normal, expected sequence (Mandler and Johnson 1977; Rumelhart 1977; Thorndyke 1977). Instead, they relocate the events in the narrative and recall it in a typical order. The incomprehensibility of poorly-structured stories also influences subjects’ summaries. Readers write better and more concise summaries for coherent than for unstructured stories (Thorndyke 1977; Kintsch et al. 1977; Kintsch and Greene 1978). These findings indicate that the violation of culturally-accepted structural conventions in stories interferes with the processing of the story information. The influence of text structure on learning has been further highlighted by studies of knowledge transfer. This work has attempted to demonstrate that knowledge of the structure of a text can influence learning of the facts in the text. For example, Thomdyke (1977) presented one group of students with two texts that possessed the same temporal, causal, and intentional relations (i.e., identical structures), but different settings, actors and events (different content). A control group read two stories that differed in both structure and content. All subjects then attempted to recall both stories. The results showed that the repetition of the story structure led to superior recall of the second text relative to the control condition. These data suggest that the initial story structure provided a framework for learning the unrelated but similarly organized facts in the second story. Other studies have produced similar results using a variety of materials (Bower 1974; Royer and Cable

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1975, 1976), although it appears that repetition of a single structure in more numerous contexts can interfere with learning of details (Bower 1974; Thomdyke and Hayes-Roth 1979). One striking aspect of this entire corpus of research is that many of the results obtained from adult subjects can be replicated with very young children. The recall superiority of important story propositions over unimportant propositions has been demonstrated with four-year olds (Poulsen et al. 1979) and with elementary school children of various ages (Christie and Schumacher 1975; Brown 1976; Mandler and Johnson 1977; Mandler 1978; Stein and Nezworski 1978; Dent and Thorndyke 1979). Children are also sensitive to story conventions of temporal sequence and causality. When story events deviate from the expected sequence, children often reorganize information in recall to correspond to its typical order (Stein and Nezworski 1978; Stein and Glenn 1978). Similar transformations occur when important information is deleted from a text. Children often add new information in recall that is an appropriate filler for the missing information (Stein and Glenn 1978). Thus, sensitivity to the typical form of narratives seems to be present even in early childhood. As this discussion illustrates, many of the results from prose learning studies are robust across different subject and materials populations. These results suggest several generalities or principles of human text processing. These generalities are summarized below. In the next section we shall consider how schema theory accounts for these data. (1) People can recall only a subset of the story information they process. (2) Some story propositions are consistently and significantly recalled better than others. (3) Subjective ratings of propositional importance are correlated with recall probability of the propositions. (4) Propositional importance predicts which propositions will be incorporated into story summaries. (5) The probability of recognition of a proposition is independent of its importance. (6) Subjects tend to recall ‘normally’ structured stories even when presented with unstructured or poorly structured stories. (7) The more explicit are the temporal, causal, and intentional relations among events in a story, the more comprehensible and memorable the story is. (8) When two stories presented in succession possess the same structure, learning of the second text is facilitated. A schema theory account of the empirical evidence Now that we have established the data to be explained, how does schema theory account for these data? As we have already indicated, several researchers have pro-

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posed that the schemata encoding prototypical story structures may be represented as sets of rewrite or production rules (Rumelhart 1975,1977; Mandler and Johnson 1977; Thorndyke 1977, 1978; Stein and Glenn 1978). Using these models, plus additional related assumptions about the structure and dynamics of schemata (Rumelhart and Ortony 1977; Mandler 1978), we attempt to explain how the data from the previous section might be predicted. In so doing, we shall describe a composite theory of schemata referred to as ST1,indicating that it is a first-generation schema theory to which many researchers have contributed. The memory schemata in ST1 are characterized as a set of grammatical rules. The rules describe the narrative elements in a typical problem-solving plot and define the permissible dependencies among those elements. Thus, the narrative grammar provides a framework for encoding, or parsing, the organiziation of text information. To illustrate, consider a simple rule for an episode: (1) Episode + Coal + Attempt’

+ Outcome.

(The ‘*’ in (1) indicates that more than one Attempt may occur.) This rule illustrates an abstract schema for the structure of episodes that is independent of any particular linguistic content. The elements that combine to form the episode may be thought of as ‘slots’ within the episode schema. These three narrative elements are matched or ‘instantiated’ for a particular story with specific facts from the story. That is, the slots in the structure take on specific values through the assignment of propositions from the story. These propositions are linked to their corresponding narrative elements, thereby forming the terminal nodes in a structural network. Furthermore, an episode serves as one element on the right side of a higherorder rule in the grammar. That is, typical stories have a setting, theme, plot, and resolution, and the plot is some number of individual episodes comprising attempts to resolve the theme. The episodes may be recursively embedded as attempts to resolve goals result in the creation of new subgoals. Thus, the application of several production rules to a particular story results in a hierarchical structure that includes the semantic content of individual propositions at the terminal nodes and the labels for the abstract narrative elements at the intermediate nodes. Since such abstract schemata express stereotypical knowledge, they constrain the form in which events can combine, while allowing flexibility in the semantic content of the events themselves. Comprehension of a story is viewed as the process of building a representation for the text using the prototypical structural patterns stored in memory. Active processes attempt to match incoming propositions from the story to narrative patterns using the constraints specified by the grammar. For example, to build a representation of an episode, matches must be found for a goal, attempts, and an outcome. The success of these match attempts determines the ease of comprehension, When matches succeed, comprehension is facilitated because relationships among successive events can be inferred from the grammar. The matched information along with its associated inferences can then be represented in

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familiar well-learned structures in long-term memory. After the text has been comprehended, it is represented hierarchically in memory. Abstract narrative knowledge is represented at the intermediate nodes in the structure, and instantiating propositions from the passage are represented at the terminal nodes. When a person is probed for his memory of the story, the structural representation is reactivated and used as a retrieval mechanism. So, when asked for verbatim recall of the story, the person attempts to access and retrieve all of the terminal nodes in correct serial order. The theory supposes that the retrieval process is a top-down traversal of the schematic structure. Beginning at the highest or most general node in the representation, the subject presumably retrieves information with a depth-first search through the hierarchy. The abstract narrative elements provide intermediate information about the type of knowledge being sought next. In particular, the narrative patterns encode the role of the to-be-recalled knowledge in the story. If the search process encounters a terminal node, that information is output as part of the recalled text. Given these general conceptions of comprehension and retrieval processes, ST1 has little difficulty accounting for the major findings outlined in the previous section. Let us turn to a brief consideration of STl’s explanations for these data. Note that the numbers used here refer to the corresponding notation in the previous section. (1) The original reaming of a prose passage is rurely perfect. ST1 can explain a subject’s imperfect or partial recall by assuming that not all story propositions are encoded in a single reading. Alternatively, even if one assumes that all story propositions are encoded, incomplete recall can still be explained by adopting appropriate assumptions about memory strength. Suppose there are probabilistic strength parameters associated with each link in the hierarchy. That is, while each proposition is presumably encoded in memory, the strength of its connection to its neighbors in the representational hierarchy is variable. Then the probability of successful retrieval of information in the hierarchy is a function of the probabilities associated with the path to that information. If any of these path strengths were zero or below some retrieval threshold, the retrieval attempt would fail and the information would not be recalled. However, even when retrieval fails and details cannot be recalled, the subject may be able to retrieve the conceptual category that characterizes the missing information. If so, he might be able to reconstruct information consistent with the functional role of the unretrieved information, based on the conceptual category. This would permit a sophisticated guessing strategy, leading to recall errors that would be functionally correct in the text as a whole even though the details of the recalled information were incorrect. (2) and (3) Important propositions are consistently recalled better than unimportant propositions. Implicit in ST1 is the assumption that the most important propositions in a story are those instantiating the highest-level narrative categories. Thus, propositions expressing the story theme or theme resolution are more important to the story than, say, attempts to achieve embedded subgoals. In terms of the

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representational hierarchy, importance is reflected in the different levels within the narrative hierarchy. High-level propositions generally express important information in the plot organization of the story whereas low-level propositions do not. Because recall is assumed to be a top-down retrieval process, the deeper in the representational hierarchy a proposition is, the longer the retrieval path to the proposition, and thus the lower the probability it can be recalled successfully. That is, important propositions should be better recalled than unimportant ones. Another way to view this prediction is that over time, recall of text-specific knowledge, especially low-level details of setting and plot, will decline faster than recall of higher-order structural information. (4)Propositional importance predicts which propositions will be included in story summaries. One implication of the hierarchical organization of knowledge is that any proposition in the structure conceptually subsumes all information directly below it. Lowerorder knowledge is a further specification or elaboration of knowledge represented in its higher-order parent, This means that an entire embedded episode may be omitted in a summarization, since its role in the narrative can be expressed at a higher level without explicit recall of the episode content. In general, the propositions selected for inclusion in a good summary correspond to the important elements of the narrative structure occurring near the top of the representational hierarchy. Thus, summary content is directly predictable from the representation: only knowledge designated as important (at the top of the hierarchy) wilI be included in summaries with high probability. (5) Although propositional importance predicts recall, all propositions are recognized equally well. This result suggesti that at comprehension time, all propositions are stored in memory in the representational hierarchy. Later recognition presumably involves direct access to a stored proposition in memory and its comparison to the test item. This process can presumably be carried out equally well for all the text propositions. However, recall requires the uncued, sequential search and retrieval of all propositions in the text. As noted above, the assumptions of topdown retrieval and association strength are sufficient to account for the levels effect in recall. In addition, however, the available evidence suggests that memory for the surface structure of a proposition is inversely related to the proposition’s importance. This effect is somewhat surprising to our general theory because it does not follow from our structure and process assumptions. Still, with a few additional assumptions, ST1 can accommodate a plausible explanation for this result. Suppose that, as Nezworski et al. (1978) have suggested, the propositions in different abstract narrative categories are distinguishable in specificity of semantic content as well as in their functional role in the story. That is, because the statements in different categories supply different types of information (e.g., settings comprise stative predications, episodes describe concrete events), the semantic content of categories may vary as a function of a category’s importance. High-level categories might be instantiated by propositions encompassing a large semantic space whereas low-level cate-

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31

gories contain precise or detailed descriptions. Thus, high-level categories would be flexible in the exact syntax for expression of a proposition’s meaning, while lowlevel propositions would be syntactically restricted. These conditions would result in better surface memory for low-level than for high-level statements because subjects would be more sensitive to low-level syntactic changes. With this ‘semantic content’ assumption, ST1 could easily explain differences in surface memory for propositions. An alternative explanation for this result depends on assumptions about subjects’ differential processing of text information. One may think a subject attempting to learn a narrative as performing two tasks: inferring and storing the structural characteristics of the plot in order to give the text coherence, and learning the particular facts - the syntactic and semantic details - in the passage. If the learner is considered to be a limited-capacity processor, then performance on this learning task might vary as a function of the differential importance of the propositions. In particular, when the to-be-learned proposition is structurally important, it behooves the subject to spend processing resources identifying and storing the organizational schema. At retrieval time, then, this knowledge can be effectively used to reconstruct the events of the story for recall. However, when the proposition does not play a central role in the plot, subjects may attend more carefully to the surface characteristics of the fact and less carefully to structural associations. Thus, knowledge of precise wordings would be superior for the less important facts, although overall processing time was equivalent for both important and unimportant facts. (6) Subjects recall normally structured stories even when presented with unstructured stories. The schemata postulated in ST1 represent typical conventions of causal and temporal sequences among the narrative elements ln a story. That is, a schema provides expectations about the order of events in the story, and influences the encoding of events into their ideal order. Consequently, if some incoming propositions are misplaced sequentially, subjects will tend to reorganize those propositions into their correct order during schema instantiation. When the schema is used to direct output of the events, the output order should reflect the ideal sequence, as dictated by the schema, rather than the anomolous sequence actually presented. Thus, misplaced story propositions are typically recalled in their ‘normal’ position in the text. (7) l%e more explicit are the temporal, causal, and intentional relations among events in a story, the more comprehensible and memorable the stoly is. According to ST1 , story comprehension depends on the use of schemata that represent coherent and purposeful event sequences in typical stories. The coherence of a story is determined by identifiable temporal, causal, and motivational relationships among the actors and events. When these relationships can be readily established, the story schemata can be easily instantiated and the story can be readily understood. Conversely, difficulty in comprehending the plot structure occurs when the temporal and causal relationships cannot be explicitly identified in the story content. When these relationships are violated or cannot be discerned, the reader cannot use the

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narrative schemata to comprehend and encode the story information. As a result, the reader is unable to exploit knowledge of the structural constraints to predict future events in the story. This should result in retardation of both comprehension and subsequent recall of the story. (8) Priming a stoly structure facilitates memory for the stoty. Comprehension of a text results in a stratified representation of both abstract narrative elements and instantiated story propositions. Thus, facilitating the creation of that representation should also facilitate comprehension. One technique to achieve this facilitation is to prime the comprehender with the appropriate plot structure. Suppose that, after processing a particular text, a reader hears a second text that is structurally identical to the first. The narrative structure created during comprehension of the first story could be activated and used to encode the information from the second story. This should facilitate comprehension relative to the case in which the second text possessed a unique narrative structure. Thus, ST1 can easily accommodate effects of proactive facilitation in the learning of identically structured stories. STl, then, appears to be sufficiently general to explain much of the available empirical data from prose experiments. In some cases, such as (1) and (5) above, additional processing assumptions were required to accommodate the experimental results within the theoretical framework. It may be noted that these assumptions were completely ad hoc, and did not follow logically from the other theoretical assumptions. Rather, they were adopted in an attempt to explain particular experimental data. With this observation as a springboard, we turn now to an evaluation of the apparent success of ST1 as an adequate theoretical framework for research in story comprehension and memory.

A critical evaluation of ST1 Philosophers of science have engaged in a continuing discussion of the criteria for judging the adequacy of theories (e.g., Kuhn 1962; Popper 1959,1963; Lakatos 1970). For the present discussion, we have adopted four of the less controversial criteria of adequacy that are appropriate for application to a rapidly evolving theoretical framework such as schema theory. In this vein, our critique may be viewed as a formative evaluation of a changing model, rather than a summative evaluation of a complete theoretical framework [ 11. The four evaluative criteria we shall consider may be labeled as plausibility, description, prediction, and testability. These requirements are listed in increasing order of constraint. That is, they differ in the degree to which they constrain or restrict the set of possible events explained by the theory. We shall now apply each of these criteria individually to ST1 , beginning with the least restrictive. [l] The distinction between formative and summa&e evaluation tion in educational settings (see Striven 1967; Markle 1976).

derives from program evalua-

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Plausibility

Probably the most fundamental requirement for a theory is that it be plausible. That is, the theory must be intuitively reasonable in light of other related facts we know, and it must give the appearance of being a valid portrayal of the behavior it presumes to model. For ST1 this means that, at least superficially, the theory must provide plausible mechanisms for the representation of knowledge structures associated with narrative discourse and the use of those structures during text processing. Consider the basic claims of ST1 as a theory of narrative knowledge. Schemata resident in memory express knowledge of typical and culturally acceptable ‘narratives’. These structures are actively used during comprehension to process incoming information. Their use is diagnostic; that is, when applied successfully they reduce uncertainty (e.g., about character motive) and the complexity of the comprehension and encoding tasks. So, for instance, they arouse story-based expectations during processing, allow for the prediction of future events, and provide a mechanism by which a person can discriminate familiar from unfamiliar event sequences (i.e., stories from non-stories). The plausibility of this model is reinforced by the close resemblance to phenomenological experience. If one is familiar with the structure, say, of television detective dramas, it is relatively easy to deduce, from watching ten minutes in the middle of a onehour show, the identity of the hero, the villian, the theme, and the eventual outcome. The notion that stereotypic narrative relationships recur frequently and that familiarity with them can facilitate comprehension is intuitively appealing. In addition, this concept has a firm historical basis. For nearly two hundred years, philosophers and psychologists have found the notion of schemata to be a useful construct for interpreting behavioral phenomena. Thus, the theory of schemata seems to be at least a plausible one. Descripion

The second principal criterion for judging a theory’s adequacy is its descriptive power. A theory should provide a clear conceptual framework and perhaps a novel lexicon for explaining some set of behavioral phenomena. Further, the behavioral explication supplied by the theory should render the phenomena more comprehensible than they were previously. In addition, the theory must distinguish itself from previous or alternative theories of related phenomena. The theory must either explain some collection of observations that could not previously be explained, or it must explain the observations more parsimoniously than alternative competing theories. ST1 is clearly outstanding as a descriptive theory. As formulated, it provides both a vocabulary and a conceptual framework for the representation of narrative knowledge. The concept of prototypical patterns of abstract narrative elements permits a level of structural analysis of texts that was not previously possible in psy-

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l? W. Thorndyke, F.R. Yekovich 1 A critique of schema theory

chology. This theoretical advance allowed psychologists to move from studies of sentence memory to studies of discourse memory. In addition, the theory has the ability to explain many of the behavioral phenomena observed when people read and remember texts. Indeed, ST1 was able to accommodate the set of results reviewed in the previous section. In fact, few experimental findings have posed serious difficulties for the theory. Prediction

This criterion requires that a theory be able to make non-trivial predictions about future (potential) observations. That is, a theory must do more than merely explain post hoc a set of available data. Rather, the theory must be sufficiently constrained so as to produce assertions about as yet unobserved behavior. The constraints required of a predictive schema theory include detailed assumptions about both the memory structures that encode knowledge (the schemata themselves) and the processes that operate on the schemata during activation, instantiation, and so on. Our formulation of ST1 has two principal shortcomings as a predictive theory. First, while the theory does entail some structural and process assumptions, it is in general so vaguely specified that it is able to explain post hoc virtually any set of available data. While many data are consistent with ST1 (as discussed in the previous section), it is difficult to find any data that are inconsistent with it. Secondly, researchers have used ST1 primarily for descriptive purposes to account for existing data. It has not been sufficiently well-specified to be used predictively. So, for example, it is not clear what ST1 would predict about memory for an anomalous datum, that is, a constituent detail in a set of information that did not fit the schema invoked to comprehend that information. Would it be well learned as a surprising stimulus (i.e., as a novel, surprising word is well remembered when placed in a categorized list), or would it be poorly learned because it did not conform to the prototypica15encoding structure? This example points out the particular weakness of ST1 in the area of process specification. While considerable development of structural assumptions has taken place during the evolution of ST1 , few detailed process mecahnisms were developed or tested empirically. The absence of these process constraints has given ST1 considerable explanatory flexibility but little predictive power. For example, in the previous section it was shown that ST1 could account for empirical generalizations (1) and (5) with the appropriate process assumptions. These results could not be predicted a priori because of the absence of these assumptions; however, it was possible to accommodate them with the theoretical framework through post hoc explanation. Thus, we conclude that ST1 is inadequate as a predictive theory.

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Testability

Our final criterion of theoretical adequacy is testability [2]. The scientific method requires a theory to be subjected to empirical tests of its predictions. Furthermore, the theory must be sufficiently constrained so as to be unable to predict and explain some outcomes. That is, it must be vulnerable to disconfirming data. The more specific and constrained a theory is, the more vulnerable it is. Further, the more vulnerable a theory is, the fewer the set of observations that confirm it. Therefore, the most preferred theories are those that are most vulnerable and make the most specific predictions. Such theories are superior to those that can accommodate either the obtained data or alternative outcomes. As we have argued above, ST1 is unsufflciently constrained to be predictive. It is, therefore, relatively impervious to disconfuming data while remaining capable of explaining post hoc most empirical results. The inability of ST1 te meet the criteria of prediction and testability seems to be due principally to a lack of theoretical development in two areas: (1) specification of the domain of knowledge for which schemata exist and are used, and (2) specification of the detailed processes that operate on and utilize the schemata. Constraining the number and type of schemata involves the explication of the conditions under which schemata can be formed and discriminated. It is currently unclear how minute in detail schemata can be and how many occurrences of an event are required to establish a schema for that event. For example, it is assumed that we have a schema for “going to a restaurant” (Schank and Abelson 1977; Bower et al. 1979). Do we also have schemata for ‘boarding a city bus” or “buying a pretzel on the street corner in New York City”? If literally thousands of such schemata exist in memory, then it is possible that any of several alternative schemata may be applicable in comprehending and encoding events in a particular situation. In fact, several researchers have suggested that, in contrast to the assumptions of ST1 , there is no single schema or set of schemata for the comprehension of narrative texts (Anderson and Pichert 1978; Baker 1978; Thorndyke 1979). The second area of theoretical weakness in ST1 is in the specification of detailed processes for manipulating and instantiating schemata. As discussed above, the absence of process dynamics in ST1 prevents predictions in situations in which schemata are presumably invoked and used. For example, how memorable is a surprising detail in a predictable sequence? What happens in memory when a schema is invoked repeatedly? Does repetitious use of a schema facilitate or interfere with its effectiveness as a memory organizer? Based on our evaluative criteria, then, ST1 falls short of expectations for a scientific theory. It seems to provide an attractive and intuitively appealing explanation of a large set of prose processing results, albeit an explanation that is difficult to [ 21 We are indebted to Rick Hayes-Roth for his comments on the role of testability in theory evaluation (see Hayes-Roth 1979).

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P. W. Thorndyke,

F.R.

Yekovich f A critique of schema theory

refute. Notice that we are not arguing that ST1 is inaccurate in its asssumptions. Indeed, the first author of this paper has used schema theory extensively as an explanatory framework for prose processing results (Thorndyke 1976,1977,1978). Our view is that the shortcomings of schema theory lie in its incompleteness, not in its inaccuracy. The incompleteness of ST1 is perhaps a natural stage in the process of theory development. We have illustrated the process of theory growth in fig. 2. The upper panel of the figure depicts how a scientific theory such as ST1 evolves into a more detailed, rigorous theory. The graphic portrays theory evolution as a growth process reflected in the number of constraints and assumptions included in the model. With each successive version of the theory (ST1 , ST2, ST3, em.), additional assumptions are introduced that constrain and refine the theory. Some of these assumptions may elaborate earlier assumptions and some may replace them. As more constraints are imposed on the theory, more testable predictions become possible, and, consequently, theoretical power grows, As shown in the lower part of fig. 2, concurrent with the growth of constraint is the growth of vulnerability. With increasing specificity, fewer potential empirical observations remain consistent with the

a ST1

Assumptions

Potential

observations

Fig. 2. A schematic

ST 3

ST 2

and constmints

consistent

with

theory

diagram of the growth of a scientific

theory.

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theory. The concentric areas labeled ST1 , ST2, and ST3 represent the subset of the space of all possible observations that are consistent with each version of the theory. The wedged areas indicate potential observations that could be obtained in a particular experimental situation (e.g., when a surprising or unexpected event occurs that does not fit the current schema). With minimal theoretical assumptions, virtually any result could be accommodated by the theory. As the theory grows in specificity, however, the number of consistent observations decreases. Thus, ST2 should make a more specific predictions about the effects of surprise and be consistent with fewer experimental outcomes than is ST1 .

Future directions for schema theory

As we have argued, the incompleteness of ST1 derives principally from its vagueness in process dynamics. It is neither sufficiently constrained to make predictions nor to be disconfumed. Recently, however, psychological researchers have begun to turn to an examination of the processes that underlie the use of memory schemata. Kintsch and van Dijk (1978) have developed a process model for the comprehension, recall, and summarization of texts with the use of memory schemata. Their model incorporates detailed assumptions about the limitations of working memory and the operations performed during processing. Along a quite different line, Thomdyke and Hayes-Roth (1979) have investigated how low-level schemata are formed and used in text comprehension. Their model details both how schemata are instantiated during learning and the costs and benefits associated with the repeated use of a schema in different contexts. In both instances, an attempt was made to operationalize some of the theoretical constructs that underlie schema theory and to test particular assumptions about their use. However, these studies have barely begun to answer the unresolved questions about schemata and their relation to psychological theory. The wealth of available data is both highly supportive of schemata as theoretical constructs and suggestive of potentially fruitful areas of further development. In conclusion, then, we shall suggest several areas that we think are central to the growth of our understanding of memory schemata. One major area for future work involves a more complete specification of the process by which schemata are acquired. That is, where do schemata come from and how do they develop? One property common to virtually all versions of schema theory is that schemata are induced from previous experience. Yet very little research by schema theorists has attempted to verify this assumption. A considerable body of research on concept learning, categorization, and prototype formation has investigated how abstractions are acquired from experience with numerous exemplars (Posner and Keele 1970; Franks and Bransford 1971; Homa and Vosburgh 1976; Rost et al. 1976; Hayes-Roth and Hayes-Roth 1977; Medin and Schaffer 1978). Methodologies employed in these studies may be useful for investi-

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gating the development of more abstract schemata for situations, events, or texts. A related problem for schema theory is that there is little understanding of the space of schemata represented in memory or the factors that determine the formation of a schema. Certainly, the frequency of occurrence and typicality of a configuration of information make it more memorable (e.g., Goldin 1978). But how do we know whether a schema for a particular concept or situation exists? Presumably, most humans have a “going to a restaurant” schema. Are there also separate schemata for events such as “attending the theater”, or “boarding the bus”? It would be useful to develop a technique for identifying memory schemata so that the domain of applicability of the theory could be made more precise. A second set of questions for schema theory is precisely how schemata are activated and used during comprehension, storage, and retrieval of information. One major limitation of current grammars for story structures is that they do not describe how semantic information in the input stream is matched to syntactic categories posited by the grammar. Such matching probably requires a set of inferential processes for linking individual facts in addition to schema recognition mechanisms. In addition, the factors that influence the activation of schemata at comprehension time need to be investigated. Traditionally, models of learning and memory have incorporated concepts such as strength and accessibility to explain the dynamics of memory activation. Schemata might well be subject to the influence of these same variables, as suggested by Thomdyke and Hayes-Roth (1979). For instance, the strength of a memory schema probably depends on the frequency and recency of its use, a fact long known for simpler memory units. These questions point to the need for research aimed at further explicating the processes surrounding the use of schemata. The determination of comprehension processes also bears on the cause of the ‘levels’ effect in text memory. We suggested earlier that the levels effect could arise from differences in retrieval of important and unimportant propositions. For example, one might presume that all story propositions are encoded equivalently, but that high-level propositions have a greater probability of recall in a top-down retrieval process in the representation hierarchy. In other words, low-level propositions are not well recalled because of a retrieval failure that is due to the search distance from the top of the structure. This hypothesis could account for the fact that recall produces a levels effect while recognition does not, as shown in the top two lines in fig. 1 (Yekovich and Thorndyke 1980). However, another possible explanation for this effect is that important propositions in the text are processed and encoded differently from low-level propositions. For instance, high-level propositions might receive multiple encodings because they are elaborated by other story propositions, whereas low level propositions are not (Anderson and Reder 1977; Kintsch and van Dijk 1978). Such redundant encoding would permit multiple retrieval paths, and consequently result in better recall for high-level than for lowlevel propositions. At the same time, memory for the exact wording of the highlevel propositions might be obscured due to the multiple encodings. This would

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produce Yekovich and Thorndyke’s (1980) result that memory for surface structure is better for low-level propositions, as shown in the bottom line on fig. 1. Finally, the levels effect might be explained by still other retrieval-based processes, such as output-editing (Anderson 1978) or inferential reconstruction (Spiro 1977). At present, schema theory is unable to discriminate among these alternative explanations of the levels effect. A third broad domain for future research concerns the specification of distinct schemata for different types of discourse. Most of the research conducted to data has investigated the memory schemata that encode the structure of goaldirected, folktale-like narratives (Rumelhart 1975, 1977; Thorndyke 1977; Mandler and Johnson 1977; Mandler 1978; Stein and Glenn 1978). The relatively simple, stereotypical structure of such stories has made them convenient targets of structural analysis. Nevertheless, a comprehensive schema theory will have to posit memory structures for a wide variety of texts. It is unlikely that a single schema is sufficient to characterize the structure of all narrative texts. In a recent study Thorndyke (1979) compared subjects’ recall of several variant forms of newspaper articles. The alternative structures included a chronological or narrative organization, a topical organization, and the original newspaper organization. Although all the stories used as materials contained a chronology of events, the narrative organization did not consistently produce superior recall. Instead, the optimal structure varied from story to story. These results suggest that distinct schemata may exist for different discourse types (see also Meyer 1977). If readers are able to use any of several organizational schemata for a text, then what characteristics of a text or of the reader trigger the adoption of a particular organizational form? One possible answer may lie in the use of more specific ‘semantic’ schemata for encoding situation and event sequences. These typical sequences, or ‘scripts’ (Schank and Abelson 1977; Bower et al. 1979) contain information about routine activities carried out in a common situation, such as eating in a restaurant, riding a bus, or visiting a dentist. Several such scripts may be appropriate for use in comprehending a single text. It is now evident that a reader’sperpective (i.e., which script is used to encode information) can influence which particulars of a story will be remembered (Anderson and Pichert 1978; Spiro 1977; Kozminsky 1977). For example, memory for a passage about the physical condition and contents of a house will vary as a function of the reader’s intent. If the reader is a ‘home buyer’, the physical condition of the house is important whereas the contents are of little value. On the other hand, if the reader is a ‘home burglar’, the contents are of prime interest. Thus, a single story may be remembered in different ways. Similarly, the orientation and interests of the reader may influence the global schema that is adopted to encode a passage. If the reader is interested in the history of events surrounding a particular situation then a narrative structure may be preferred. If, on the other hand, the narrative information is only incidental to the main point or conclusion of the story, then an organization (e.g., a topical structure) that emphasizes the main point might be more appropriate.

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While we have tried to point to some of the gaps in our knowledge of memory schemata and unanswered questions raised by current schema theories, we have tried to maintain a balanced view of the entire research enterprise. We consider memory schemata a rich and powerful domain in which to investigate the structure and processes of human memory. Clearly, our understanding of memory has been enriched by the constructs provided by schema theorists. Within this context, we consider the unresolved issues raised here as challenges to future researchers in this new and promising paradigm.

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Perv W. Thomdyke received his B.A. degree from Yale University in 1971, and his Ph.D. degree in Psychology from Stanford in 1975. Since 1975 Dr. Thorndyke has worked in the Information Sciences Department of The Rand Corporation, where he presently holds the title of Computer Scientist. While at Rand, he has served as Principal Investigator on studies of text understanding and learning (conducted for the Defense Advanced Research Projects Agency), spatial and locational cognition (conducted for the Office of Naval Research), and team training and performance (conducted for the Office of Naval Research). Frank R. Yekovich received his B.A. from the University of Colorado in 1972, and his Ph.D. in Educational Psychology from Arizona State University in 1977. From 1977 to 1979 Dr. Yekovich worked as a Research Psychologist for the U.S. Army Research Institute. Since 1979 he has served as an Assistant Professor of Education at The Catholic University of America. Dr Yekovich’s research interests include psycholinguistics and text comprehension and memory.