7Background: Previous schizophrenia research involving the "beads task" has suggested an association between delusions and 2 reasoning biases: (1) "jumping to conclusions" (JTC), whereby early, resolute decisions are formed on the basis of little evidence and (2) overadjustment of probability estimates following a single instance of disconfirmatory evidence. In the current study, we used a novel JTC-style paradigm to provide new information about a cognitive operation common to these 2 reasoning biases. Methods: Using a task that required participants to rate the likelihood that a fisherman was catching a series of black or white fish from Lake A and not Lake B, and vice versa, we compared the responses of 4 groups (healthy, bipolar, nondelusional schizophrenia and delusional schizophrenia) when we manipulated 2 elements of the Bayesian formula: incoming data and prior odds. Results: Regardless of our manipulations of the Bayesian formula, the delusional schizophrenia group gave significantly higher likelihood ratings for the lake that best matched the colour of the presented fish, but the ratings for the nonmatching lake did not differ from the other groups. Limitations: The limitations of this study include a small sample size for the group of severely delusional patients and a preponderance of men in the schizophrenia sample. Conclusion: Delusions in schizophrenia are associated with hypersalience of evidence-hypothesis matches but normal salience of nonmatches. When the colour of the incoming data is uniform (fish of only one colour), this manifests as JTC early in a series, and when the colour of incoming data varies (both black and white fish), this manifests as an overadjustment midseries. This account can provide a unifying explanation for delusion-associated performance patterns previously observed in the beads task in schizophrenia.
A neuropsychological paradigm is introduced that provides a measure of a bias against disconfirmatory evidence (BADE), and its correspondence with delusions in people with schizophrenia and schizoaffective disorder was investigated. Fifty-two patients diagnosed with schizophrenia or schizoaffective disorder (36 were acutely delusional) and 24 healthy control participants were presented with delusion-neutral pictures in each trial, and were asked to rate the plausibility of four written interpretations of the scenario depicted by that picture. Subsequently, new pictures that provided background information about the depicted scenario were successively presented, and participants were requested to adjust their ratings, taking into account this new information. Two of the interpretations appeared tenable initially but ultimately proved to be implausible, one appeared untenable initially but eventually proved to be plausible, and one appeared untenable at all stages. A BADE was observed for delusional compared to non-delusional patients, as well as for all patients compared to controls. In addition, regardless of symptom profile, patients were more accepting of implausible interpretations than controls. The present work suggests that deficits in reasoning may contribute to the maintenance of delusions via an impairment in the processing of disconfirmatory evidence.
In prior studies, it was observed that patients with schizophrenia show abnormally high knowledge corruption (i.e., high-confident errors expressed as a percentage of all high-confident responses were increased for schizophrenic patients relative to controls). The authors examined the conditions under which excessive knowledge corruption occurred using the Deese-Roediger-McDermott paradigm. Whereas knowledge corruption in schizophrenia was significantly greater for false-negative errors relative to controls, no group difference occurred for false-positive errors. The groups showed a comparable high degree of confidence for false-positive recognition of critical lure items. Similar to findings collected in elderly participants, patients, but not controls, showed a strong positive correlation between the number of recognized studied items and false-positive recognition of the critical lure.Memory dysfunctions have been ascribed a key role in many pathogenetic models of schizophrenia (e.g., Hemsley, 1994). The literature suggests that both memory recall and recognition are severely compromised in schizophrenic patients relative to healthy participants (see Aleman, Hijman, de Haan, & Kahn, 1999, for a meta-analysis; see also Heinrichs & Zakzanis, 1998). However, as of yet, no schizophrenia-specific mnestic aberration has been identified. In contrast to an extensive body of research on forgetting in schizophrenia (i.e., false-negative errors), until recently the investigation of false-positive errors has attracted little attention. Depending on the paradigm used, some studies have provided evidence for enhanced false-positive memory errors in schizophrenia (Stirling, Hellewell, & Hewitt, 1997), whereas others have been unable to detect any group differences (e.g., Brébion, Amador, Smith, & Gorman, 1997;Moritz, Heeren, Andresen, & Krausz, 2001). Weiss, Dodson, Goff, Schacter, and Heckers (2002) have suggested that task demands and material may represent moderators for these inconsistent findings. In this study, increased false recognition in schizophrenia was evident for word, but not picture, material and only occurred in an experimental condition in which correct task performance necessitated retrieval of item-specific information (i.e., recollection of an item's spatial and temporal context).Another neglected area of memory research in schizophrenia is the investigation of memory confidence. In two source-monitoring studies Moritz, Woodward, & Ruff, 2003), evidence for a dissociation between objective and subjective memory performance in schizophrenia was found (i.e., measured performance accuracy vs. subjective evaluation of one's performance). Results from both investigations support the claim that patients with schizophrenia, irrespective of psychopathological status, display an enhanced confidence for false memory responses relative to healthy controls, whereas no group differences occurred for confidence in correct decisions. In the second study , 12% of responses made by schizophrenic patients with high confi...
Working memory (WM) is one of the most impaired cognitive processes in schizophrenia. Functional magnetic resonance imaging (fMRI) studies in this area have typically found a reduction in information processing efficiency but have focused on the dorsolateral prefrontal cortex. In the current study using the Sternberg Item Recognition Test, we consider networks of regions supporting WM and measure the activation of functionally connected neural networks over different WM load conditions. We used constrained principal component analysis with a finite impulse response basis set to compare the estimated hemodynamic response associated with different WM load condition for 15 healthy control subjects and 15 schizophrenia patients. Three components emerged, reflecting activated (task-positive) and deactivated (task-negative or default-mode) neural networks. Two of the components (with both task-positive and task-negative aspects) were load dependent, were involved in encoding and delay phases (one exclusively encoding and the other both encoding and delay), and both showed evidence for decreased efficiency in patients. The results suggest that WM capacity is reached sooner for schizophrenia patients as the overt levels of WM load increase, to the point that further increases in overt memory load do not increase fMRI activation, and lead to performance impairments. These results are consistent with an account holding that patients show reduced efficiency in task-positive and task-negative networks during WM and also partially support the shifted inverted-U-shaped curve theory of the relationship between WM load and fMRI activation in schizophrenia.
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