Weak suppression of visual context in chronic schizophrenia

The Müller-Lyer illusion as a tool for schizophrenia screening

The perceptual deficit hypothesis for schizophrenia is based on more general models of normal human visual perception, which have traditionally postulated that objects must compete for attention and processing space in the visual system. Recent evidence suggests that susceptibility of schizophrenics to the Müller-Lyer (ML) illusion may be a marker of vulnerability, detectable in prodromic patients, but disappearing with the progression of the illness. This illusion consists of overestimating the length of a straight line with converging arrowheads at the ends, while underestimating those with diverging arrowheads. Although the ML illusion has been shown to occur in touch as well as vision, it is not known whether abnormal contextual suppression extends to other sensory modalities in schizophrenics. Another challenge consists in verifying whether different visual parameters of the illusion which favor the magnocellular and parvocellular systems would have diverse ML illusion effects in schizophrenia. In this review we present data showing the degree of illusion in capuchin monkeys (Cebus spp.), a possible animal model for schizophrenia. To this end, a computer program was developed to conduct experiments in humans and non-human primates, allowing the display of illusory figures, manipulation of the stimuli's exposure time, interval between stimuli and number of trials. In the non-primate experiments, the visual illusion test based on achromatic ML illusion figures indicated the presence of the ML illusory effect in 10 capuchin monkeys. These results suggest that Cebus might be a good model for the experimental study of schizophrenia.

What's in a face? Effects of stimulus duration and inversion on face processing in schizophrenia

A number of studies show deficits in early-stage visual processing in schizophrenia. Deficits are also seen at more complex levels, such as ability to discriminate faces. This study investigated the "face inversion" effect, which reflects intrinsic cortical processing within the ventral visual stream, as well as contrast sensitivity, which reflects low-level visual processing, in order to evaluate integrity of specific stages of face processing in schizophrenia. Patients with schizophrenia and controls discriminated between pairs of upright or inverted faces or houses that had been manipulated to differ in the shape of the parts or the spatial distance among parts. The duration threshold for above chance performance on upright stimuli was obtained for patients using a house discrimination task. Contrast sensitivity was assessed for gratings of three spatial frequencies ranging from 0.5 to 21 cycles/degree. Patients needed significantly longer time to obtain 70% correct for upright stimuli and showed decreased contrast sensitivity. Increased duration threshold correlated with reduced contrast sensitivity to low (magnocellular-biased) but not medium or high spatial frequency stimuli. Using increased durations, patients showed significant inversion effects that were equivalent to those of controls on the face part and spacing tasks. Like controls, patients did not show inversion effects on the house tasks. These findings show that patients have difficulty integrating visual information as shown by increased duration thresholds. However, when faces were presented at these longer duration thresholds, patients showed the same relative processing ability for upright vs. inverted faces as controls, suggesting preserved intrinsic processing within cortical face processing regions. Similar inversion effects for face part and spacing for both groups suggest that they are using the same holistic face processing mechanism.

Measuring specific, rather than generalized, cognitive deficits and maximizing between-group effect size in studies of cognition and cognitive change

While cognitive impairment in schizophrenia is easy to demonstrate, it has been much more difficult to measure a specific cognitive process unconfounded by the influence of other cognitive processes and noncognitive factors (eg, sedation, low motivation) that affect test scores. With the recent interest in the identification of neurophysiology-linked cognitive probes for clinical trials, the issue of isolating specific cognitive processes has taken on increased importance. Recent advances in research design and psychometric theory regarding cognition research in schizophrenia demonstrate the importance of (1) maximizing between-group differences via reduction of measurement error during both test development and subsequent research and (2) the development and use of process-specific tasks in which theory-driven performance indices are derived across multiple conditions. Use of these 2 strategies can significantly advance both our understanding of schizophrenia and measurement sensitivity for clinical trials. Novel data-analytic strategies for analyzing change across multiple conditions and/or multiple time points also allow for increased reliability and greater measurement sensitivity than traditional strategies. Following discussion of these issues, trade-offs inherent to attempts to address psychometric issues in schizophrenia research are reviewed. Finally, additional considerations for maximizing sensitivity and real-world significance in clinical trials are discussed.

Altered center-surround motion inhibition in schizophrenia

BACKGROUND

Schizophrenia is a brain disorder that spans across biological and behavioral levels. The links between altered neural circuitry and abnormal behaviors are yet to be understood. Visual motion perception has been established in basic neuroscience and may provide an opportunity to link different levels of brain functions in schizophrenia. Center-surround interaction is a ubiquitous neural mechanism underlying the organization of visual information over different spatial locations.

METHODS

We applied a psychophysical paradigm to examine center-surround interaction in schizophrenia. Patients (n = 24) and control subjects (n = 33) judged the direction of a moving random dot pattern (RDP, center) with and without the presence of another concentric surrounding RDP (surround).

RESULTS

The presence of a moving surround shifted the perceptual judgments of center motion in the opposite direction from the surround in both subject groups but the magnitude of the perceptual shift was significantly larger in patients. The increased perceptual shift was not correlated with psychotic symptoms, which were mild in this patient sample, or antipsychotic medication.

CONCLUSIONS

The increased perceptual shift suggests that the putative surround suppression on visual motion perception is abnormally increased in schizophrenia. This result provides perceptual evidence for altered basic inhibitory control of visual motion context in schizophrenia.

The translation of cognitive paradigms for patient research

Many cognitive tasks have been developed by basic scientists to isolate and measure specific cognitive processes in healthy young adults, and these tasks have the potential to provide important information about cognitive dysfunction in psychiatric disorders, both in psychopathology research and in clinical trials. However, several practical and conceptual challenges arise in translating these tasks for patient research. Here we outline a paradigm development strategy--which involves iteratively testing modifications of the tasks in college students, in older healthy adults, and in patients--that we have used to successfully translate a large number of cognitive tasks for use in schizophrenia patients. This strategy makes it possible to make the tasks patient friendly while maintaining their cognitive precision. We also outline several measurement issues that arise in these tasks, including differences in baseline performance levels and speed-accuracy trade-offs, and we provide suggestions for addressing these issues. Finally, we present examples of 2 experiments, one of which exemplifies our recommendations regarding measurement issues and was a success and one of which was a painful but informative failure.

Building a clinically relevant cognitive task: case study of the AX paradigm

Tasks developed for basic cognitive neuroscience are often ill suited for experimental psychopathology. The development of the expectancy variant of AX continuous performance task to test theories about context processing in schizophrenia is used as an illustration of how this has been done in one research program. Four design principles are recommended: tasks should (1) have a foundation in existing literature and therefore stay as close as possible to an existing task; (2) be simple, which is frequently accomplished by paring down a task to evaluate the function of interest; (3) probe a mechanism of interest, with conditions that selectively manipulate this mechanism; and (4) have the potential to distinguish a specific deficit on the mechanism of interest from a generalized impairment. Data from a number of studies support several aspects of context-processing theory; however unpredicted results have also been reported. The development of the expectancy AX paradigm continues, and future developments that may enhance its usefulness are also described.

Visual perception and its impairment in schizophrenia

Much work in the cognitive neuroscience of schizophrenia has focused on attention, memory, and executive functioning. To date, less work has focused on perceptual processing. However, perceptual functions are frequently disrupted in schizophrenia, and thus this domain has been included in the CNTRICS (Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia) project. In this article, we describe the basic science presentation and the breakout group discussion on the topic of perception from the first CNTRICS meeting, held in Bethesda, Maryland on February 26 and 27, 2007. The importance of perceptual dysfunction in schizophrenia, the nature of perceptual abnormalities in this disorder, and the critical need to develop perceptual tests appropriate for future clinical trials were discussed. Although deficits are also seen in auditory, olfactory, and somatosensory processing in schizophrenia, the first CNTRICS meeting focused on visual processing deficits. Key concepts of gain control and integration in visual perception were introduced. Definitions and examples of these concepts are provided in this article. Use of visual gain control and integration fit a number of the criteria suggested by the CNTRICS committee, provide fundamental constructs for understanding the visual system in schizophrenia, and are inclusive of both lower-level and higher-level perceptual deficits.

Contextual suppression and protection in schizophrenic patients

INTRODUCTION

Contextual processing is often strongly deteriorated in schizophrenic patients as found, for example, in higher cognitive as well as lower visual paradigms. In visual detection tasks, impoverished contextual facilitation was attributed to aberrant excitatory neural circuits. On the other hand, we found contextual suppression, possibly related to neural inhibition, to be fast and intact in a visual backward masking task. Here, we combine a suppressive with a "protective" paradigm to further our understanding of the contextual deficiencies of schizophrenic patients in visual information processing.

METHODS

Twenty three schizophrenic patients and 18 healthy controls were asked to discriminate the offset direction of a vernier target, which was followed by one of a variety of masks for several stimulus onset asynchronies (SOAs).

RESULTS

As in previous studies, patients needed clearly longer SOAs than controls. However, when longer SOAs were taken into account, increases as well as decreases in backward mask strength had comparable effects in patients and controls.

CONCLUSIONS

From these results, we suggest that complex spatial processing is fast and intact in schizophrenic patients.

Perceptual organization in ketamine users: preliminary evidence of deficits on night of drug use but not 3 days later

N-methyl-D-aspartate (NMDA)-receptor antagonists such as ketamine can induce transient schizophrenia-like symptoms and cognitive dysfunctions in healthy volunteers similar to those observed in patients with schizophrenia. Perceptual organization deficits have been documented in schizophrenia and are thought to be related to some symptoms associated with the illness. The current study was designed to determine whether people who repeatedly self-administer ketamine would also show deficits in perceptual organization. Using a psychophysically well-controlled measure of contour integration, we compared a group of recreational users (n = 16) to a group of poly-drug using controls (n = 16). Contour integration performance was measured on the night of drug use and 3 days later when drug free. The results showed that on the night of drug use, ketamine produced a dysfunction in contour integration however, this was not present 3 days later when drug free. Levels of dissociation were also higher in ketamine users only on the night of drug use. These preliminary data provide some support for the role of NMDA-receptor hypofunctioning in dysfunctional coordination of cognitive activity.

Collinear contextual suppression in schizophrenic patients

Schizophrenic patients show aberrancies of contextual processing over a broad range. Of particular importance are low level contextual deficiencies since they might cause higher level processing deficits. It was previously found that schizophrenic patients reveal diminished contextual facilitation in visual detection tasks taken as an indication of a modified neural circuitry. Here, we show that contextual suppression is not affected. Sixteen schizophrenic patients and sixteen healthy controls participated in a backward masking task in which a vernier target was followed by a masking grating. In accordance with a previous publication, schizophrenic patients needed longer SOAs between the vernier and the grating onset to obtain a performance level comparable to healthy controls. To study contextual processing we added single collinear lines to the grating. These lines yielded a strong impairment of performance in patients and controls. This impairment is comparable between the two groups if SOAs were individually adjusted. Hence, whereas contextual facilitation is deficient, contextual suppression seems to be intact in schizophrenic patients.

The cerebellum and motor dysfunction in neuropsychiatric disorders

The cerebellum is densely interconnected with sensory-motor areas of the cerebral cortex, and in man, the great expansion of the association areas of cerebral cortex is also paralleled by an expansion of the lateral cerebellar hemispheres. It is therefore likely that these circuits contribute to non-motor cognitive functions, but this is still a controversial issue. One approach is to examine evidence from neuropsychiatric disorders of cerebellar involvement. In this review, we narrow this search to test whether there is evidence of motor dysfunction associated with neuropsychiatric disorders consistent with disruption of cerebellar motor function. While we do find such evidence, especially in autism, schizophrenia and dyslexia, we caution that the restricted set of motor symptoms does not suggest global cerebellar dysfunction. Moreover, these symptoms may also reflect involvement of other, extra-cerebellar circuits and detailed examination of specific sub groups of individuals within each disorder may help to relate such motor symptoms to cerebellar morphology.

Weakened center-surround interactions in visual motion processing in schizophrenia

Schizophrenia is often accompanied by a range of visual perception deficits, with many involving impairments in motion perception. The presence of perceptual abnormalities may impair neural processes that depend on normal visual analysis, which in turn may affect overall functioning in dynamic visual environments. Here, we examine the integrity of suppressive center-surround mechanisms in motion perception of schizophrenic patients. Center-surround suppression has been implicated in a range of visual functions, including figure-ground segregation and pursuit eye movements, visual functions that are impaired in schizophrenia. In control subjects, evidence of center-surround suppression is found in a reduced ability to perceive motion of a high-contrast stimulus as its size increases. This counterintuitive finding is likely a perceptual correlate of center-surround mechanisms in cortical area MT. We now show that schizophrenic patients exhibit abnormally weak center-surround suppression in motion, an abnormality that is most pronounced in patients with severe negative symptoms. Interestingly, patients with the weakest surround suppression outperformed control subjects in motion discriminations of large high-contrast stimuli. This enhanced motion perception of large high-contrast stimuli is consistent with an MT abnormality in schizophrenia and has a potential to disrupt smooth pursuit eye movements and other visual functions that depend on unimpaired center-surround interactions in motion.