Altered perception of apparent motion in schizophrenia spectrum disorder

Heightened perception of illusory motion is associated with symptom severity in schizophrenia patients

Abnormal perceptual processing in schizophrenia may contribute to the development of positive symptoms such as hallucinations. Experimental findings suggest that such abnormalities result from impaired processing of local signals into complex cortical representations. Because complex processing is needed to generate the perception of illusory motion from local signals, deteriorated perception of illusory motion would be expected in schizophrenia. However, findings are mixed, and the relationship between complex motion processing and symptoms is unclear. Illusions with multiple flow components (e.g. rotation/expansion) are known to strongly engage specialized complex processing mechanisms that may be abnormal in schizophrenia, but have not yet been investigated. We used a recently constructed paradigm based on the Pinna-Brelstaff illusion to manipulate complex-flow illusory perception in a quantitative manner and probe associations with dimensional symptoms. In 102 patients and 90 controls, perceived speed and perceptual variability for the PBF were measured across a range of parameters. Meanwhile, eye movement was recorded and gaze parameters were analysed to examine effects on illusory perception. Our results showed that patients experienced faster illusory rotation than controls, while they made fewer eye fixations. This heightened illusory perception was significantly correlated with positive and general, but not negative, symptom scores. Our results indicate that unusual processing of complex-flow motion in patients may be specifically related to dimensional symptoms, which could provide a promising strategy for parsing heterogeneity in the schizophrenia syndrome. This further highlights the role of motion perception abnormalities in the pathophysiology of schizophrenia, thus encouraging future investigation into visual remediation therapeutics.

Examining motion speed processing in schizophrenia using the flash lag illusion

Research on visual perception in schizophrenia suggests a deficit in motion processing. Specifically, difficulties with discriminating motion speed are commonly reported. However, speed discrimination tasks typically require participants to make judgments about the difference between two stimuli in a two-interval forced choice (2IFC) task. Such tasks not only tap into speed processing mechanisms, but also rely on higher executive functioning including working memory and attention which has been shown to be compromised in schizophrenia. We used the Flash Lag illusion to examine speed processing in patients with schizophrenia. Based on previous research showing a strong dependence between motion speed and the illusion magnitude, we expected a deficit in speed processing to alter this relationship. A motion processing deficit in patients would also predict overall reductions in perceived lag. We found the magnitude and speed dependence of the Flash Lag illusion to be similar in patients and controls. Together, the findings suggest no general abnormality in motion speed processing in schizophrenia.

Local versus global and retinotopic versus non-retinotopic motion processing in schizophrenia patients

Schizophrenia impairs cognitive functions as much as perception. For example, patients perceive global motion in random dot kinematograms less strongly, because, as it is argued, the integration of the dots into a single Gestalt is complex and therefore deteriorated. Similarly, the perception of apparent motion is impaired, because filling-in of the illusory trajectory requires complex processing. Here, we investigated very complex motion processing using the Ternus-Pikler display. First, we tested whether the perception of global apparent motion is impaired in schizophrenia patients compared to healthy controls. The task requires both the grouping of multiple elements into a coherent Gestalt and the filling-in of its illusory motion trajectory. Second, we tested the perception of rotation in the same stimulus, which in addition requires the computation of non-retinotopic motion. Contrary to earlier studies, patients were not impaired in either task and even tended to perform better than controls. The results suggest that complex visual processing itself is not impaired in schizophrenia patients.

Investigating vision in schizophrenia through responses to humorous stimuli

The visual environment of humans contains abundant ambiguity and fragmentary information. Therefore, an early step of vision must disambiguate the incessant stream of information. Humorous stimuli produce a situation that is strikingly analogous to this process: Funniness is associated with the incongruity contained in a joke, pun, or cartoon. Like in vision in general, appreciating a visual pun as funny necessitates disambiguation of incongruous information. Therefore, perceived funniness of visual puns was implemented to study visual perception in a sample of 36 schizophrenia patients and 56 healthy control participants. We found that both visual incongruity and Theory of Mind (ToM) content of the puns were associated with increased experienced funniness. This was significantly less so in participants with schizophrenia, consistent with the gestalt hypothesis of schizophrenia, which would predict compromised perceptual organization in patients. The association of incongruity with funniness was not mediated by known predictors of humor appreciation, such as affective state, depression, or extraversion. Patients with higher excitement symptoms and, at a trend level, reduced cognitive symptoms, reported lower funniness experiences. An open question remained whether patients showed this deficiency of visual incongruity detection independent of their ToM deficiency. Humorous stimuli may be viewed as a convenient method to study perceptual processes, but also fundamental questions of higher-level cognition.

Crowding, grouping, and gain control in schizophrenia

Visual paradigms are versatile tools to investigate the pathophysiology of schizophrenia. Contextual modulation refers to a class of paradigms where a target is flanked by neighbouring elements, which either deteriorate or facilitate target perception. It is often proposed that contextual modulation is weakened in schizophrenia compared to controls, with facilitating contexts being less facilitating and deteriorating contexts being less deteriorating. However, results are mixed. In addition, facilitating and deteriorating effects are usually determined in different paradigms, making comparisons difficult. Here, we used a crowding paradigm in which both facilitation and deterioration effects can be determined all together. We found a main effect of group, i.e., patients performed worse in all conditions compared to controls. However, when we discounted for this main effect, facilitation and deterioration were well comparable to controls. Our results indicate that contextual modulation can be intact in schizophrenia patients.

Altered alpha brain oscillations during multistable perception in schizophrenia

Schizophrenia is a complex mental disorder with impairments in integrating sensory and cognitive functions, leading to severe problems in coherent perception. This impairment might be accelerated during multistable perception. Multistable perception is a phenomenon, where a visual pattern gives rise to at least two different perceptual representations. We addressed this issue by assessing event-related alpha oscillations during continuous viewing of an ambiguous and unambiguous control stimulus. Perceptual reversals were indicated by a manual response, allowing differentiation between phases of reversion and non-reversion (that is perceptual stability) in both tasks. During the ambiguous task, patients and controls showed a comparable number of perceptual reversals. Alpha amplitudes in patients were larger in non-reversion phases, accompanied by a stronger decrease of alpha activity preceding the perceptual reversal. This group difference was pronounced for lower alpha activity and not apparent during the unambiguous task. This indicates that ambiguous perception taps into the specific deficits that patients experience in maintaining coherent perception. Given that top-down influences in generating a meaningful percept seems to be low in patients, they appear more dependent on sensory information. Similar, bottom-up mechanisms might be more important in triggering perceptual reversals in patients than in controls.

Clinical correlates associated with cognitive dysfunction in people with schizophrenia

AIMS

The purpose of the present study was to investigate the correlation between cognitive function and clinical variables in people with schizophrenia.

METHODS

The subjects were 61 stabilized outpatients with schizophrenia (DSM-IV). Their mean age was 40.1 (SD = 12.2) years. All subjects gave written informed consent to participate in the research. Cognitive function was evaluated using the Brief Assessment of Cognition in Schizophrenia. Clinical symptoms were assessed using the Positive and Negative Syndrome Scale, the Calgary Depression Scale for Schizophrenia, and the Drug-Induced Extrapyramidal Symptoms Scale.

RESULTS

The Positive and Negative Syndrome Scale Negative syndrome score was significantly correlated with verbal memory score (r = -0.37, P < 0.01), working memory score (r = 0.38, P < 0.01), attention and speed of information processing score (r = -0.51, P < 0.01), verbal fluency score (r = -0.39, P < 0.01), and composite score (r = -0.54, P < 0.01). In addition, the Drug-Induced Extrapyramidal Symptoms Scale score was significantly correlated with attention and speed of information processing (r = -0.45, P < 0.01), and composite score (r = -0.41, P < 0. 01). Dose of antipsychotics and anti-Parkinson drugs was not significantly correlated with the Brief Assessment of Cognition in Schizophrenia scores.

CONCLUSIONS

These results indicate that cognitive dysfunction of people with schizophrenia might be associated with negative and drug-induced extrapyramidal symptoms, suggesting that their minimization would be important for improving cognitive dysfunction.

Cognitive binding in schizophrenia: weakened integration of temporal intersensory information

Cognitive functioning is based on binding processes, by which different features and elements of neurocognition are integrated and coordinated. Binding is an essential ingredient of, for instance, Gestalt perception. We have implemented a paradigm of causality perception based on the work of Albert Michotte, in which 2 identical discs move from opposite sides of a monitor, steadily toward, and then past one another. Their coincidence generates an ambiguous percept of either "streaming" or "bouncing," which the subjects (34 schizophrenia spectrum patients and 34 controls with mean age 27.9 y) were instructed to report. The latter perception is a marker of the binding processes underlying perceived causality (type I binding). In addition to this visual task, acoustic stimuli were presented at different times during the task (150 ms before and after visual coincidence), which can modulate perceived causality. This modulation by intersensory and temporally delayed stimuli is viewed as a different type of binding (type II). We show here, using a mixed-effects hierarchical analysis, that type II binding distinguishes schizophrenia spectrum patients from healthy controls, whereas type I binding does not. Type I binding may even be excessive in some patients, especially those with positive symptoms; Type II binding, however, was generally attenuated in patients. The present findings point to ways in which the disconnection (or Gestalt) hypothesis of schizophrenia can be refined, suggesting more specific markers of neurocognitive functioning and potential targets of treatment.

Perceptual organization impairment in schizophrenia and associated brain mechanisms: review of research from 2005 to 2010

Perceptual organization (PO) refers to the processes by which visual information is structured into coherent patterns such as groups, contours, perceptual wholes, and object representations. Impairments in PO have been demonstrated in schizophrenia since the 1960s and have been linked to several illness-related factors including poor premorbid functioning, poor prognosis, and disorganized symptoms. This literature was last reviewed in 2005. Since then, electrophysiological (electroencephalographic, event-related potential, and magnetoencephalographic) and fMRI studies in both patient and nonpatient samples have clarified brain mechanisms involved in the impairment, and additional behavioral studies in patients and nonpatients have clarified the computational mechanisms. In addition, data now exist on the functional consequences of PO impairments, in terms of secondary difficulties in face processing, selective attention, working memory, and social cognition. Preliminary data on drug effects on PO and on changes in response to treatment suggest that anomalies in PO may furnish a biomarker for the integrity of its associated biological mechanisms. All of this recent evidence allows for a clearer picture of the nature of the impairment and how it relates to broader aspects of brain and behavioral functioning in schizophrenia.

Abnormal visual motion processing in schizophrenia: a review of research progress

Motion processing represents a perceptual domain in which dynamic visual information is encoded to support the perception of movement. Research over the last decade has found a variety of abnormalities in the processing of motion information in schizophrenia. The abnormalities span from discrimination of basic motion features (such as speed) to integration of spatially distributed motion signals (such as coherent motion). Motion processing involves visual signals across space and time and thus presents a special opportunity to examine how spatial and temporal information is integrated in the visual system. This article surveys the behavioral and neuroimaging studies that probe into the spatial integration of motion information in schizophrenia. An emerging theme from these studies points to an imbalanced regulation of spatial interaction processes as a potential mechanism mediating different levels of abnormal motion processing in schizophrenia. The synthesis of these mechanism-driven studies suggests that further investigation of the neural basis and functional consequences of this abnormal motion processing are needed in order to render a basic biomarker for assessment and intervention of cognitive dysfunction in this mental disorder.