A breakdown of event schemas in patients with schizophrenia: an examination of their script for dining at restaurants
Introduction
Language impairment is one prominent characteristic of schizophrenia. Schizophrenic patients often manifest incoherent speech patterns that contain delusional ideas or inappropriate associations. Empirically, performance deficits have been reported for schizophrenic patients on several language tasks including confrontation naming (Barr et al., 1989), auditory and reading comprehension (Silverberg-Shalev et al., 1981), word definition (Paulsen et al., 1994) and verbal fluency (Allen et al., 1993, Goldberg et al., 1995).
Several hypotheses have been proposed to explain the language deficits of patients with schizophrenia. Early hypotheses included deficiency in deductive reasoning (Von Domarus, 1944), over-inclusive thinking (Cameron, 1939, Cameron, 1954), excessive concreteness of thought (Goldstein, 1944), regression (Gardner, 1931, Kasanin, 1944) and loosening of association (Bleuler, 1911). Some recent evidence also suggests that the language deficits of schizophrenic patients can be attributed to the social perceptual deficits in which those patients were impaired in understanding abstract concepts and emotional aspects of particular situations (Penn et al., 1997, Corrigan and Nelson, 1998). In addition, another hypothesis suggests that the language impairment observed in patients with schizophrenia may be attributed to a breakdown of semantic memory.
Semantic memory was used by Tulving (1985) to describe the stored knowledge for use in language that includes a broad spectrum of information such as the interrelationships among concepts (Collins and Loftus, 1975, Anderson, 1983), and the abstract understanding of past experiences and events (Bartlett, 1932, Schank, 1975, Rumelhart and Ortony, 1977, Schank and Abelson, 1977). Semantic memory was also proposed to be organized in a hierarchical fashion with the most general concepts at the top and more specific features at the bottom (Rosch et al., 1976). A ‘bottom-up’ breakdown of semantic knowledge is a loss of the specific attributes of some concepts with a relative preservation of more general knowledge.
Evidence supporting the hypothesis of a breakdown of semantic knowledge in patients with schizophrenia came primarily from findings that schizophrenic patients demonstrated impairment on tasks of category verification (Chen et al., 1994), word association (Johnson et al., 1964, Lisman and Cohen, 1972), categorization (McKay et al., 1996), naming (McKay et al., 1996), similarity judgment (Paulsen et al., 1996), and lexical priming (Spitzer et al., 1993, Ober et al., 1995). Although these studies have provided compelling evidence that the organization of semantic knowledge is abnormal in schizophrenia, they were focused on examining the organization of isolated concepts (e.g. the relative closeness between dog and cat). Hence, relatively little is known about the semantic organization of past experiences or typical events (e.g. what is the procedure for doing laundry) in schizophrenia.
It has been well understood that our memories of past experiences or acquired knowledge are organized in a meaningful way. Several theories, including the relatively general ideas of schema (Bartlett, 1932) to a more defined and orderly proposal of scripts (Schank and Abelson, 1977), have been developed to conceptualize the organization of past experiences. Bartlett (1932) first proposed the concept schema to refer to memory of generalized concepts underlying situations. Schank (1975) refined the idea and suggested that our knowledge about stereotypic events, such as going to a restaurant, can be encoded according to the parts and sequences of the event. For instance, going to a restaurant may be divided into four parts, namely, entering, ordering, eating and exiting. The four sub-events come one after another, in a particular sequence. Schank used the term script to describe these phenomena.
It has been shown that common events have a very similar structure from individual to individual. For example, when subjects were asked to name the 20 most important concepts in an episode of going to a restaurant, concepts such as sit down, look at menu, order, eat, pay bill, and leave were mentioned by at least 73% of the subjects (Bower et al., 1979). The present study adopted the version of script theory proposed by Schank (1975), and utilized the norms reported by Bower et al. (1979) to examine event schemas in patients with schizophrenia.
The present experiment consisted of three sub-tasks, namely, free-recall, frequency judgment and sequencing. In the free-recall task, subjects would be asked to describe typical events that happen when going to a restaurant. The typicality and the recall order of the items would be analyzed to reveal subjects’ general conceptualization of an event. However, given that performance on the free-recall task requires an effortful retrieval, any abnormality may be attributed to a deficit of accessing the semantic knowledge rather than a breakdown of the structure. To distinguish among these possibilities, the frequency judgment and sequencing tasks, which require relatively less retrieval effort, were administered. The frequency judgment task provides information on the individual’s understanding of the relative typicality of various items in the schema of going to a restaurant. The sequencing task provides information about the subject’s knowledge on the sequential order of the items in the schema. If a breakdown in the structure of semantic knowledge is a prominent characteristic of schizophrenic patients, they would be impaired in recalling, judging and sequencing the items in an event schema.
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Subjects
There were 40 patients meeting DSM-IV criteria for schizophrenia, and 40 age- and education-matched normal individuals who consented to participate in the study (Table 1). All patients were recruited from the psychiatric unit of the Chinese University of Hong Kong, which is located at the Prince of Wales and Shatin Hospitals. Patients were diagnosed by senior psychiatrists using a structured interview. The normal individuals were healthy volunteers who were members at the hospitals, and they
Free-recall task
The total number of responses in the free-recall task for the normal individuals (mean=15.88, S.D.=8.85) and the patients with schizophrenia (mean=9.10, S.D.=3.66) were significantly different (t=4.38, P<0 001). To evaluate the pattern of recall in the sub-sections, repeated measures ANOVA with group as an independent variable and number of items generated in each sub-section as dependent variables was performed. Given that the Mauchly sphericity test was significant (W=0.81, P<0.01), the
Discussion
Results of the present study suggest that event schemas of the patients with schizophrenia are abnormal as compared with their age-and education-matched counterparts. That is, although their event schemas contain general structure, they are characterized by a deterioration of detailed information and by an incoherent organization. Specifically, when patients with schizophrenia were asked to describe an episode of going to a restaurant, their description consisted of four sub-sections (i.e.
Acknowledgements
This study was in part funded by the Chinese University of Hong Kong Direct Grant. We thank Qian-lin Chen, Maggie Ng, Issac Kwok, Mei-Chun Cheung and Jeanny Tan for assistance with data collection and management, and Dr. Twila Tardif for insightful comments on an earlier version of this article.
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