Effects of stimulus structure and target-distracter similarity on the development of visual memory representations in schizophrenia

Introduction. In a previous study (Silverstein, Bakshi, Chapman, & Nowlis, 1998a, Cognitive Neuropsychiatry) we demonstrated that while schizophrenia patients showed similar learning curves as nonpatient controls when determining whether a configural pattern of elements has been seen before or not, they did not demonstrate any learning curve with nonconfigural stimuli (in contrast to controls). Methodological limitations of that study, however, precluded generalisability of those effects.Methods. In the present study, therefore, different groups of schizophrenia patients (n = 18) and controls (n = 22) were administered a modified version of the familiarity judgement task used in Silverstein et al. (1998a). In the new version of the task: (1) the patterns that repeated were different for each participant; and (2) half of the nonrepeating patterns were configural and half were nonconfigural.Results. These indicated stronger perceptual learning effects for the configural compared to the nonconfigural patterns, and overall better performance and more pronounced learning effects for the control group.Conclusions. The data provide further evidence for a schizophrenia-related impairment in perceptual organisation and in the ability to develop memory representations for novel stimuli.     

Reduced top-down influences in contour detection in schizophrenia

Introduction. Chronic schizophrenia patients have previously demonstrated performance deficits in contour integration tasks. The purpose of this study was to investigate whether schizophrenia patients, spanning a range of illness severity, would demonstrate responsiveness to manipulations that recruit top-down processing strategies involving learning and sequencing effects in a contour integration task. Methods. We administered a contour integration test over four consecutive days and in two different presentation conditions each day. In one condition, the stimuli were administered in order of increasing difficulty, and in the other they were presented in random order. The order in which these two conditions were presented was counterbalanced across days and participants. In addition, a nonschizophrenia psychotic disorders control group was included to determine if past findings of a contour integration deficit in schizophrenia could be replicated in the presence of a symptomatically similar control group. Results. All groups demonstrated similar learning curves across the four days and generally similar overall levels of performance, with the exception of the group of the most chronic schizophrenia patients. In addition, the order in which the stimuli were presented to subjects affected their performance, with higher scores achieved for all groups in the condition where the stimuli were presented in increasing order of difficulty. Interaction effects revealed that the effects of order presentation were greater for nonpatient than for psychotic patients. Conclusions. These data are further evidence that perceptual organization impairments in schizophrenia are illness severity-related, and that schizophrenia patients as a whole are less sensitive to top-down manipulations in this type of task.     

Early processing deficits in object working memory in first-episode schizophreniform psychosis and established schizophrenia

BACKGROUND: While there are many studies showing working-memory deficits in schizophrenia there are only a few that disentangle impairments for working-memory subprocesses such as perceptual, attentional, mnemonic and executive function. METHOD: In this study of delay-dependent memory, 55 patients with schizophreniform psychosis, 50 with established schizophrenia and 56 healthy controls were investigated. Using the delayed matching-to-sample task from the Cambridge Neuropsychological Test Automated Battery (CANTAB), performance deficits were found in both patient groups after controlling for age and pre-morbid IQ. RESULTS: Even after controlling for simultaneous matching-to-sample ability (i.e. perceptual matching), impaired performance in both patient groups was found as soon as the stimuli were no longer present. Impaired performance was not due to different types of errors in patients versus controls. Performance in both patient groups was comparable, except for a slight decrease of overall task performance. This suggests that the deficit is relatively stable during the course of the illness. CONCLUSIONS: Our results suggest a deficit in patients with psychotic illness in the initial processes necessary to actively maintain information, such as the ability to form an internal representation of complex objects.     

Configural processing in face recognition in schizophrenia

Introduction. There is currently substantial literature to suggest that patients with schizophrenia are impaired on many face-processing tasks. This study investigated the specific effects of configural changes on face recognition in groups of schizophrenia patients. Methods. In Experiment 1, participants identified facial expressions in upright faces and in faces inverted from their upright orientation. Experiments 2 and 3 examined recognition memory for faces and other non-face objects presented in upright and inverted orientations. Experiment 4 explored recognition of facial identity in composite images where the top half of one face was fused to the bottom half of another face to form a new face configuration. Results. In each experiment, the configural change had the same effect on face recognition for the schizophrenia patients as it did for control participants. Recognising inverted faces was more difficult than recognising upright faces, with a disproportionate effect of inversion on faces relative to other objects. Recognition of facial identity in face-halves was interfered with by the formation of a new face configuration. Conclusion. Collectively, these results suggest that people with schizophrenia rely on configural information to recognise photographs of faces.     

The perception of self-produced sensory stimuli in patients with auditory hallucinations and passivity experiences: evidence for a breakdown in self-monitoring

BACKGROUND: To test the hypothesis that certain psychotic symptomatology is due to a defect in self-monitoring, we investigated the ability of groups of psychiatric patients to differentiate perceptually between self-produced and externally produced tactile stimuli. METHODS: Responses to tactile stimulation were assessed in three groups of subjects: schizophrenic patients; patients with bipolar affective disorder or depression; and normal control subjects. Within the psychiatric groups subjects were divided on the basis of the presence or absence of auditory hallucinations and/or passivity experiences. The subjects were asked to rate the perception of a tactile sensation on the palm of their left hand. The tactile stimulation was either self-produced by movement of the subject's right hand or externally produced by the experimenter. RESULTS: Normal control subjects and those psychiatric patients with neither auditory hallucinations nor passivity phenomena experienced self-produced stimuli as less intense, tickly and pleasant than identical, externally produced tactile stimuli. In contrast, psychiatric patients with these symptoms did not show a decrease in their perceptual ratings for tactile stimuli produced by themselves as compared with those produced by the experimenter. This failure to show a difference in perception between self-produced and externally produced stimuli appears to relate to the presence of auditory hallucinations and/or passivity experiences rather than to the diagnosis of schizophrenia. CONCLUSIONS: We propose that auditory hallucinations and passivity experiences are associated with an abnormality in the self-monitoring mechanism that normally allows us to distinguish self-produced from externally produced sensations.     

Schizophrenia patients' perceptual biases in response to positively and negatively valenced emotion chimeras

BACKGROUND: In a prior study, we observed that schizophrenia patients display atypical perceptual biases in response to emotional (happy/neutral) facial chimeras. METHODS: The present study was an attempt to replicate and extend those findings, using emotional stimuli with negative affective valence (angry/neutral chimeras) as well as positive valence, and including more than one type of non-affective facial comparison task. We compared schizophrenia patients (N = 37) and controls (N = 48) on free-vision tasks that typically yield left spatial field biases indicative of right hemisphere activation. There were six chimera tasks, including two emotion (happy, angry) chimeras, two non-emotion (gender, age) chimeras and two non-face (dots, gradients) chimeras. RESULTS: We observed a Group x Task interaction, with schizophrenia patients displaying significantly less of the expected left spatial perceptual bias in response to the happy/neutral chimeras and the angry/neutral chimeras relative to the controls. In contrast, the patients and controls did not differ in terms of their response to the Gender, Age, Dots, or Gradients tasks. CONCLUSIONS: These findings are consistent with the assertion that, compared with healthy controls individuals with schizophrenia perceive emotion differently.     

Impaired distractor inhibition in patients with schizophrenia on a negative priming task

BACKGROUND: Numerous studies have suggested, via the interpretation of negative priming effects, that subjects with schizophrenia are less able than controls to inhibit irrelevant distracting information. Further issues concerning impairment in inhibitory processes are investigated here. First, recent research has revealed that negative priming (NP) effects can be caused by different processes, distractor inhibition or perceptual review. Therefore, conclusions concerning reduced inhibition in patients with schizophrenia are not possible from previous NP research. Secondly, previous NP studies have required subjects to identify some feature of the target. This is the first study to examine NP that uses a spatial task in patients with schizophrenia. METHOD: Twenty-eight subjects with schizophrenia and 28 age and sex matched non-psychiatric control subjects completed a computerized NP task that eliminated the possible contribution of perceptual review. RESULTS: Subjects with schizophrenia had reduced levels of NP compared to control subjects on this spatial NP task (t = 2.46, P < 0.02). Current age, positive, negative or total PANNS scores did not correlate with negative priming scores, but post hoc analyses revealed that clozapine-treated patients had significantly greater levels of negative priming than patients receiving typical antipsychotic medications. CONCLUSIONS: The present experiment eliminated the contribution of perceptual review to negative priming and demonstrated that when a pure measure of inhibition is taken on a localization task, patients with schizophrenia were less able to inhibit irrelevant distracting stimuli. The fact that NP was reduced in a spatial task suggested a more diffuse reduction in inhibition than previous studies that examined only identification-based responses.     

Age-related changes in processing faces from detection to identification: ERP evidence

We examined the ability of people 70 to 90 years old to apply global, configural, and featural face-processing strategies. In addition we investigated age-related changes in the ability to categorize faces at basic, subordinate, and individual levels. Using the N170 potential as index of early face processing and the P300 component as index of categorical decision making and effort, we found significant age-related perceptual changes which slowed and somewhat impaired face processing. Specifically, older participants had problems integrating face features into global structures, demonstrating enhanced dependence on distal global information. They did not apply configural computations by default while processing faces which suggests that, unless identification is required, they process faces only at a basic level. These perceptual changes could be the cause for slower and less accurate subordinate categorization, particularly when it is based on details. At the neural levels face processing was not right-lateralized, reflecting excessive involvement of the left hemisphere in perception leading to a more general reduction of interhemispheric asymmetry. In addition we found excessive but nonselective activation of frontal regions adding support to the view that executive control and particularly inhibition of irrelevant input are reduced in the elderly.     

How patients with schizophrenia use the internet: qualitative study

Background

The Internet is an important source of health information for people with psychiatric conditions. Little is known about the way patients with schizophrenia use the Internet when it comes to issues related to their illness. Data on their specific needs, difficulties, and the consequences related to Internet use are lacking.

Objective

Our objective was to investigate the nature and subjective consequences of health-related Internet use among patients with schizophrenia.

Methods

In all, 26 individual semistructured interviews were conducted and analyzed qualitatively in groups of 4 until theoretical saturation was achieved.

Results

Study results suggest that the Internet is an influential source of illness-related information for patients with schizophrenia. Many aspects of their behavior around the Internet resemble those of individuals not afflicted by mental illness. Importantly, problems specific to patients with schizophrenia were stimulus overflow, an inability to deal with the abundance of information, difficulties with concentration, lack of energy, paranoid ideas, symptom provocation, and the need to distance themselves from illness-related topics as part of the recovery process. Internet information was subjectively perceived as having the potential to significantly change patients’ attitudes toward medication and their relationships with doctors.

Conclusions

These findings provide insight into how individuals with schizophrenia handle illness-related Internet information. The data could contribute to the continuous development of Internet-based interventions and offer novel approaches to optimizing traditional treatment options.     

Hearing a voice in the noise: auditory hallucinations and speech perception

BACKGROUND: It has recently been suggested that auditory hallucinations are the result of a criterion shift when deciding whether or not a meaningful signal has emerged. The approach proposes that a liberal criterion may result in increased false-positive identifications, without additional perceptual deficit. To test this hypothesis, we devised a speech discrimination task and used signal detection theory (SDT) to investigate the underlying cognitive mechanisms. METHOD: Schizophrenia patients with and without auditory hallucinations and a healthy control group completed a speech discrimination task. They had to decide whether a particular spoken word was identical to a previously presented speech stimulus, embedded in noise. SDT was used on the accuracy data to calculate a measure of perceptual sensitivity (Az) and a measure of response bias (beta). Thresholds for the perception of simple tones were determined. RESULTS: Compared to healthy controls, perceptual thresholds were higher and perceptual sensitivity in the speech task was lower in both patient groups. However, hallucinating patients showed increased sensitivity to speech stimuli compared to non-hallucinating patients. In addition, we found some evidence of a positive response bias in hallucinating patients, indicating a tendency to readily accept that a certain stimulus had been presented. CONCLUSIONS: Within the context of schizophrenia, patients with auditory hallucinations show enhanced sensitivity to speech stimuli, combined with a liberal criterion for deciding that a perceived event is an actual stimulus.     

Temporal context and the organisational impairment of memory search in schizophrenia

Introduction. An influential theory of schizophrenic deficits in executive function suggests that patients have difficulty maintaining and utilising an internal contextual representation, whose function is to ensure that stimuli are processed in a task-appropriate manner. In basic research on episodic memory, retrieved-context theories propose that an internal contextual representation is critically involved in memory search, facilitating the retrieval of task-appropriate memories. This contextual machinery is thought to give rise to temporal organisation during free recall: the tendency for successive recall responses to correspond to items from nearby positions on the study list. If patients with schizophrenia have a generalised contextual deficit, then this leads to the prediction that these patients will exhibit reduced temporal organisation in free recall.

Methods. Using a combination of classic and recently developed organisational measures, we characterised recall organisation in 75 patients with schizophrenia and 72 nondisordered control participants performing a multi-trial free-recall task.

Results. Patients with schizophrenia showed diminished temporal organisation, as well as diminished subjective organisation of their recall sequences relative to control participants. The two groups showed similar amounts of semantic organisation during recall.

Conclusions. The observation of reduced temporal organisation in the patient group is consistent with the proposal that the memory deficit in schizophrenia can be characterised as a deficit in contextual processing.     

Perceptual Organisation of Configural and Visual Patterns in Schizophrenia: Effects of Repeated Exposure

Recent evidence suggests that although schizophrenia patients can process aspects of visual form to which the visual system is ''hard-wired'' to respond, they are deficient in consolidating novel, unstructured visual information into memory traces, thus limiting the assessment of meaning and the generation of top-down influences to guide further processing. This hypothesis was tested with 18 chronic schizophrenia patients and 18 controls using a familiarity judgement task. As predicted, schizophrenia patients' ability to recognise a highly structured visual pattern increased as a function of experience. In contrast, recognition performance for an unstructured pattern did not improve even after 120 exposures. These data suggest that schizophrenia is characterised by a reduced ability to initiate experience-based changes in the visual system, wherein a group of noncontiguous elements that recur together and that are behaviourally relevant begins to be processed as a single unit. These data, and significant correlations between abnormal task performance and disorganised symptoms are consistent with recent neurophysiological models of schizophrenia.     

You must be looking at me: The nature of gaze perception in schizophrenia patients

Introduction. Accurately identifying gaze direction is an important component of successful social interaction. Preliminary research indicates that schizophrenia patients have deficits in gaze perception, but the nature of this deficit is still unclear. The current study investigates whether nonspecific perceptual abnormalities could explain gaze perception deficits and whether schizophrenia patients show a direct gaze bias in their judgement. Methods. Fifteen chronic schizophrenia patients and nineteen normal control participants made a direct gaze judgement for eyes in a face, and a centre judgement for a geometric shape in a scrambled face. Results. The data show that schizophrenia patients are as accurate as healthy control subjects at identifying direct gaze when it occurs but they are more likely to misinterpret averted gaze as directed at them. The pattern of results indicates that this tendency to endorse direct gaze is not a consequence of a perceptual deficit in judging angular displacement. Conclusions. Schizophrenia patients have a self-referential bias in judging the direction of gaze that could lead to the misinterpretation of another person's intentions during the course of social interaction.     

Attentional modulation of perceptual organisation in schizophrenia

Introduction. Previous studies indicated impaired perceptual organisation in schizophrenia. This study investigated lateral connection and attentional modulation in early visual cortex of schizophrenia patients.

Methods. Contrast threshold was measured for a central Gabor patch, flanked with orthogonal and collinear Gabor patches. In the attended condition, participants performed a concurrent vernier task by determining the spatial offset of the flankers.

Results. The controls (n=25) had lower contrast thresholds in the collinear condition than in the orthogonal condition, whereas the schizophrenia patients (n=43) did not benefit from the presence of collinear flankers. This deficit was not ameliorated by attentional modulation. Antipsychotic medication did not affect the performance.

Conclusions. These results suggest that lateral connections are impaired in early visual cortex of schizophrenia patients. This deficit cannot be restored by top-down attentional modulation of target-flanker interactions.     

Sensory perceptual limitation in schizophrenia.

Sensory perception and selective attention capacity of schizophrenic patients have drawn particular interest. Schizophrenic patients show a peculiar deficit in screening and processing of incoming sensory data. Review of the literature suggests a breakdown in the selective-inhibitory function of attention in schizophrenic patients facing multiple sensory modalities. Although disorganization of attention is a focal point in schizophrenic perception, the influence of memory on the perceptual process deserves further investigation. Distracting sensory stimuli particularly of an auditory nature seem to interfere with visual perception and motor performance in these patients. Avoidance of sensory overload and improving selective attention through psychotherapy though of some therapeutic value, requires further exploration. A case of a young schizophrenic patient exposed to distractible environmental stimuli was presented and discussed.     

Contradiction processing in schizophrenia

ABSTRACT

Introduction: Patients with schizophrenia present clinically with difficulties in manipulating contradictory information in the form of loose associations, surface contradictions and delusional beliefs. It is to date unclear whether patients can detect and process information that contradicts their beliefs and prior knowledge and whether this capacity is related to their symptoms and the nature of contradictory stimuli (e.g., personally significant information, emotional information).

Methods: We probed contradiction processing in patients with schizophrenia and healthy controls using sentence verification tasks that involve self-referential judgements (Experiment 1) and general knowledge (Experiment 2), while manipulating the emotional content of the stimuli.

Results: We found no differences between patients and controls either on reaction time (Experiment 1 & 2) or accuracy measures (Experiment 1).

Conclusions: Our results show no general impairment in contradiction processing in schizophrenia. Rather, failures to detect and correct contradictions in symptoms such as formal though disorder or delusions could arise through a complex interplay between executive dysfunctions, stress and the emotional content of the information.     

A redefinition of odor mixture quality

Odor mixtures are perceived as different from (configural) or the same as (elemental) their components. Recent studies (L. M. Kay, C. A. Lowry, & H. A. Jacobs, 2003; C. Wiltrout, S. Dogra, & C. Linster, 2003) propose that component structural or perceptual similarities predict configural properties of binary mixtures. The authors evaluated this in rats using 4 binary mixtures with varying structural similarity (eucalyptol-benzaldehyde, eugenol-benzaldehyde, octanol-octanal, and [+/-]-limonene). The range of tested ratios for each mixture was determined by the components' vapor pressures. Three results are presented: (a) No mixture maintains purely elemental or configural properties for all concentration ratios, (b) structural similarity or dissimilarity does not predict configural or elemental perception, and (c) overshadowing is significant in responses to all odor sets. The authors offer more precise definitions of elemental and configural properties and overshadowing as they relate to odor mixture perception.     

Developmental changes in elemental and configural perception of odor mixtures in young rabbits

Development can change the way organisms represent their environment and affect their behavior. In vision, complex stimuli are treated as the sum of their elements (elemental perception) in children or as a whole (configural perception) in adults. However, the influence of development in elemental/configural perception has never been tested in olfaction. Here we explored this issue in young rabbits, which are known to perceive during the neonatal period certain binary odor mixtures elementally and others weak configurally. Using conditioning and behavioral testing procedures, we set out six experiments evaluating the putative evolution of their odor perception between birth and weaning. Results highlighted that between postnatal days 2 and 9 the perception of an initially weak configural mixture became robust configural while that of two elemental mixtures did not. Additional switches from elemental to configural perception were observed at postnatal day 24. The use of a chemically more complex senary mixture resulted also in a shift from weak to robust configural perception between postnatal days 2 and 9. Thus, the perception of certain odor mixtures may rapidly evolve toward a more holistic mode in young rabbits, which may help simplifying their representation of the environment once out of the nest.     

Lateral interactions in the visual cortex of patients with schizophrenia and bipolar disorder

BACKGROUND: Schizophrenia is associated with perceptual organization deficits and abnormal neuronal connectivity has been described in early visual areas. The purpose of this study was to investigate the functional integrity of lateral connections in early visual areas of patients with schizophrenia and type I bipolar disorder with a history of psychosis. METHOD: Twenty-four out-patients with schizophrenia, 22 out-patients with bipolar disorder, and 20 healthy control subjects participated in the study. Using a computer-assisted psychophysical test, contrast thresholds were measured for centrally presented target stimuli (Gabor patches), which were surrounded by two collinear flankers. Target-to-flanker distances were 0, 1, 2, 3, 4, 6, 9 and 122. Psychophysical measures were contrast threshold changes at each target-to-flanker distance compared with baseline thresholds determined for isolated targets with no flankers. Clinical measures included IQ, positive, negative, and depressive symptoms. Results. In patients with schizophrenia, flankers did not facilitate contrast detection for target stimuli at 2-6 lambda distances compared to controls [effect size (Cohen's d): 1.25-1.42]. The inhibitory effect of flankers (0 and 1lambda) and contrast thresholds in the absence of flankers were spared. Patients with bipolar disorder did not differ from the controls. Medicated and non-medicated patients displayed similar performances. Positive and negative symptoms and depression did not correlate with contrast threshold values. CONCLUSIONS: Excitatory lateral connections in early visual cortex are specifically impaired in patients with schizophrenia, which may contribute to perceptual disorders such as unclear seeing, partial or skewed sight, disrupted rectilinearity, and abnormal figure-ground segregation.     

Visual-perceptual dysfunctions are possible endophenotypes of schizophrenia: evidence from the psychophysical investigation of magnocellular and parvocellular pathways

Visual information processing is impaired in schizophrenia patients and their biological relatives. The authors measured vernier thresholds in 72 schizophrenia patients, their 86 siblings, and 60 healthy control subjects. Subjects were asked to detect the direction of the horizontal displacement of 2 stimuli (left or right). During magnocellular (M) pathway tests, stimuli were dots with low contrast (5%) or counterphase-modulated gratings (25 Hz). For parvocellular (P) pathway tests, isoluminant blue-red dots with yellow-green background were used. Results revealed that patients with schizophrenia and their siblings were more impaired in M pathway conditions than in P pathway conditions. There was no color-specific impairment. The patients and their siblings displayed lower performances on tests of executive functions, psychomotor speed, and verbal memory compared with the controls. Visual-perceptual and neuropsychological data did not correlate. In conclusion, M pathway dysfunction is a potential endophenotype of schizophrenia.