Magnocellular contributions to impaired motion processing in schizophrenia

Patients with schizophrenia show impairments in motion processing, along with deficits in lower level processing primarily involving the magnocellular visual pathway. The present study investigates potential magnocellular contributions to impaired motion processing in schizophrenia using a combined neurophysiological and behavioral approach. As compared to prior motion studies in schizophrenia, thresholds were determined for both incoherent and coherent visual motion. In this study, velocity discrimination thresholds were measured for schizophrenia patients (n=14) and age-matched normal control subjects (n=16) using a staircase procedure. Early visual processing was evaluated using steady-state visual evoked potentials (ssVEP), with stimuli biased toward activation of either the magnocellular or parvocellular visual pathways through luminance contrast manipulation. Patients with schizophrenia showed poor velocity discrimination for both incoherent and coherent motion, with no significant group x task interaction. Further, when coherent motion performance was measured at individually determined incoherent motion thresholds, accuracy levels for patients were similar to controls, also indicating similarity of deficit for incoherent vs. coherent motion discrimination. Impairments in velocity discrimination correlated significantly with reduced amplitude of ssVEP elicited by magnocellular -- but not parvocellular -- selective stimuli. This study demonstrates that deficits in motion processing in schizophrenia are significantly related to reduced activation of the magnocellular visual system. Further, this study supports and extends prior reports of impaired motion processing in schizophrenia, and indicates significant bottom-up contributions to higher-order cognitive impairments.     

Motion perception in schizophrenia

BACKGROUND: Eye-tracking dysfunction has been found in many patients with schizophrenia and in about 40% of their first-degree biological relatives. We hypothesized that a deficit in motion processing is associated with eye-tracking dysfunction because both motion signals and the brain regions responsible for processing motion signals are implicated in the generation of smooth pursuit. We examined several aspects of visual perception, including motion perception, in patients with schizophrenia. METHODS: To evaluate motion perception, contrast sensitivity for velocity discrimination was measured in patients with schizophrenia (n=15) and normal control subjects (n=18). Contrast sensitivities for orientation discrimination and contrast detection were measured as control tasks. RESULTS: Patients with schizophrenia showed significantly lower contrast sensitivity (ie, higher thresholds) than normal controls for the discrimination of small velocity differences (eg, 11 vs 9 degrees/s). This reduction in contrast sensitivity was severe (up to 10-fold) in about 40% of the patients. No group differences were found on the other tasks. CONCLUSION: The discrimination of small velocity differences is impaired in a subgroup of patients with schizophrenia.     

Independent deficits of visual word and motion processing in aging and early Alzheimer's disease

We tested whether visual processing impairments in aging and Alzheimer's disease (AD) reflect uniform posterior cortical decline, or independent disorders of visual processing for reading and navigation. Young and older normal controls were compared to early AD patients using psychophysical measures of visual word and motion processing. We find elevated perceptual thresholds for letters and word discrimination from young normal controls, to older normal controls, to early AD patients. Across subject groups, visual motion processing showed a similar pattern of increasing thresholds, with the greatest impact on radial pattern motion perception. Combined analyses show that letter, word, and motion processing impairments are independent of each other. Aging and AD may be accompanied by independent impairments of visual processing for reading and navigation. This suggests separate underlying disorders and highlights the need for comprehensive evaluations to detect early deficits.     

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination

BACKGROUND: Since Kraepelin's early distinction between bipolar disorder and schizophrenia, it has been assumed that these disorders represent two different pathophysiological processes, although they share many clinical symptoms. Previous studies showed that velocity discrimination, a sensitive psychophysiological measure of the visual motion system, is deficient in schizophrenia. Here we examined whether the motion processing impairment found in schizophrenia also occurs in bipolar disorder. METHODS: We compared 16 bipolar patients, 25 schizophrenic patients, and 25 normal controls on a velocity discrimination task. We measured the psychophysical threshold for velocity discrimination and contrast detection (as a control task) in all subjects. RESULTS: Bipolar patients showed normal velocity discrimination thresholds at intermediate velocities, the range in which velocity cues dominate velocity discrimination, and at low velocities. Schizophrenic patients, however, showed elevated velocity discrimination thresholds at intermediate and low velocities. At higher velocities, both bipolar and schizophrenic patients showed elevated thresholds. All subjects showed normal contrast detection thresholds. CONCLUSIONS: Normal velocity discrimination in the intermediate range of velocity indicates unimpaired motion processing in bipolar disorder. The abnormal velocity discrimination of both schizophrenic and bipolar patients at higher velocities may reflect impaired temporal processing rather than impaired motion processing per se. These results suggest that the pathophysiological processes of bipolar disorder and schizophrenia diverge at the stage of visual motion processing, a sensory component mediated primarily in the extrastriate cortex.     

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination

BackgroundSince Kraepelin's early distinction between bipolar disorder and schizophrenia, it has been assumed that these disorders represent two different pathophysiological processes, although they share many clinical symptoms. Previous studies showed that velocity discrimination, a sensitive psychophysiological measure of the visual motion system, is deficient in schizophrenia. Here we examined whether the motion processing impairment found in schizophrenia also occurs in bipolar disorder.MethodsWe compared 16 bipolar patients, 25 schizophrenic patients, and 25 normal controls on a velocity discrimination task. We measured the psychophysical threshold for velocity discrimination and contrast detection (as a control task) in all subjects.ResultsBipolar patients showed normal velocity discrimination thresholds at intermediate velocities, the range in which velocity cues dominate velocity discrimination, and at low velocities. Schizophrenic patients, however, showed elevated velocity discrimination thresholds at intermediate and low velocities. At higher velocities, both bipolar and schizophrenic patients showed elevated thresholds. All subjects showed normal contrast detection thresholds.ConclusionsNormal velocity discrimination in the intermediate range of velocity indicates unimpaired motion processing in bipolar disorder. The abnormal velocity discrimination of both schizophrenic and bipolar patients at higher velocities may reflect impaired temporal processing rather than impaired motion processing per se. These results suggest that the pathophysiological processes of bipolar disorder and schizophrenia diverge at the stage of visual motion processing, a sensory component mediated primarily in the extrastriate cortex.     

Motion integration deficits are independent of magnocellular impairment in Parkinson's disease

Motion processing involves multiple hierarchical steps, from the magnocellular pathway, sensitive to high temporal frequency modulations, to subsequent motion integration within the visual cortical dorsal stream. We have tested whether motion integration deficits in mild Parkinson disease (PD) can be explained by visual deficits in earlier processing nodes. Contrast sensitivity deficits in the magnocellular pathway, were compared with speed discrimination of local dots moving in random directions, speed and direction discrimination of moving surfaces and motion integration as measured by 2D coherence thresholds (n = 27). We have found that low-level magnocellular impairment in PD does not explain deficits in subsequent steps in motion processing. High-level performance was abnormal in particular for tasks requiring perception of coherently moving surfaces. Motion coherence deficits were predictive of visuomotor impairment, corroborating a previous magnetic stimulation study in normal subjects. We conclude that dorsal stream deficits in PD have a high-level visual cortical basis independent of low-level magnocellular damage.     

Compromised late-stage motion processing in schizophrenia.

BACKGROUND: Visual motion processing is compromised in schizophrenia, as shown in deficient velocity discrimination. Processing of motion signals comprises progressive stages along the geniculate-striate-extrastriate-cortex pathway. Based on neurophysiologic and brain lesion studies, a velocity discrimination deficit can implicate early-stage motion processing if it is contrast-dependent or late-stage motion processing if it is contrast-independent. METHODS: To determine which stage underlies the deficient velocity discrimination in schizophrenia, we examined the effects of visual contrast on velocity discrimination. We measured velocity discrimination thresholds in schizophrenia patients (n = 34) and normal control subjects (n = 17) at both low and high contrasts, using each subject's contrast detection threshold to equate contrast levels. RESULTS: Schizophrenia patients showed poor velocity discrimination that improved little with high contrast, whereas normal control subjects showed enhanced velocity discrimination with increased contrast. CONCLUSIONS: The finding that the velocity discrimination deficit in schizophrenia is independent of contrast modulation implicates the later, rather than the earlier, stages of motion processing, which is mediated in the extrastriate cortex.     

Facial emotion perception in Chinese patients with schizophrenia and non-psychotic first-degree relatives

Although there is a consensus that patients with schizophrenia have certain deficits in perceiving and expressing facial emotions, previous studies of facial emotion perception in schizophrenia do not present consistent results. The objective of this study was to explore facial emotion perception deficits in Chinese patients with schizophrenia and their non-psychotic first-degree relatives. Sixty-nine patients with schizophrenia, 56 of their first-degree relatives (33 parents and 23 siblings), and 92 healthy controls (67 younger healthy controls matched to the patients and siblings, and 25 older healthy controls matched to the parents) completed a set of facial emotion perception tasks, including facial emotion discrimination, identification, intensity, valence, and corresponding face identification tasks. The results demonstrated that patients with schizophrenia performed significantly worse than their siblings and younger healthy controls in accuracy in a variety of facial emotion perception tasks, whereas the siblings of the patients performed as well as the corresponding younger healthy controls in all of the facial emotion perception tasks. Patients with schizophrenia also showed significantly reduced speed than younger healthy controls, while siblings of patients did not demonstrate significant differences with both patients and younger healthy controls in speed. Meanwhile, we also found that parents of the schizophrenia patients performed significantly worse than the corresponding older healthy controls in accuracy in terms of facial emotion identification, valence, and the composite index of the facial discrimination, identification, intensity and valence tasks. Moreover, no significant differences were found between the parents of patients and older healthy controls in speed after controlling the years of education and IQ. Taken together, the results suggest that facial emotion perception deficits may serve as potential endophenotypes for schizophrenia.     

Impaired visual recognition of biological motion in schizophrenia

BACKGROUND: Motion perception deficits have been suggested to be an important feature of schizophrenia but the behavioral consequences of such deficits are unknown. Biological motion refers to the movements generated by living beings. The human visual system rapidly and effortlessly detects and extracts socially relevant information from biological motion. A deficit in biological motion perception may have significant consequences for detecting and interpreting social information. METHODS: Schizophrenia patients and matched healthy controls were tested on two visual tasks: recognition of human activity portrayed in point-light animations (biological motion task) and a perceptual control task involving detection of a grouped figure against the background noise (global-form task). Both tasks required detection of a global form against background noise but only the biological motion task required the extraction of motion-related information. RESULTS: Schizophrenia patients performed as well as the controls in the global-form task, but were significantly impaired on the biological motion task. In addition, deficits in biological motion perception correlated with impaired social functioning as measured by the Zigler social competence scale [Zigler, E., Levine, J. (1981). Premorbid competence in schizophrenia: what is being measured? Journal of Consulting and Clinical Psychology, 49, 96-105.]. CONCLUSION: The deficit in biological motion processing, which may be related to the previously documented deficit in global motion processing, could contribute to abnormal social functioning in schizophrenia.     

Early stage vision in schizophrenia and schizotypal personality disorder

Previous studies of visual perception have reported deficits in contrast sensitivity and dot motion discrimination in schizophrenia. We tested whether these deficits also appear in schizotypal personality disorder (SPD). SPD appears to be genetically and symptomatically related to schizophrenia, but without the marked psychosocial impairment associated with psychotic disorders. The present study investigated contrast sensitivity for moving and static gratings, form discrimination and dot motion discrimination in 24 patients with schizophrenia or schizoaffective disorder (SZ), 16 individuals with SPD, and 40 control subjects. SZ, but not SPD subjects, showed impairments on tests of contrast sensitivity for static and moving gratings, form discrimination in noise, and dot motion discrimination. Visual performance did not differ between medicated SZ patients and patients withdrawn from medication. These results confirm early stage visual deficits in schizophrenia regardless of medication status. SPD subjects, in contrast, show intact early stage visual processing despite the presence of marked schizotypal symptoms.     

Influence of antipsychotic medication on pain perception in schizophrenia

A number of clinical observations indicate that pain processing might be disturbed in psychotic disorders such as schizophrenia. Only a few studies have investigated pain perception in schizophrenia. The main objective of this study was the investigation of thresholds of warmth perception (WP), thermal pain onset (TPO) and thermal pain tolerance (TPT) in acute schizophrenic patients and the influence of antipsychotic medication on the patients' responses. We investigated 23 schizophrenic subjects who had been not received antipsychotic treatment for 8 weeks, and we then reassessed them 3 days later after the introduction of neuroleptics. Acute symptoms of schizophrenia were measured using the Scales for the Assessment of Positive and Negative Symptoms. Thresholds were determined by a contact thermode on both volar wrists. Schizophrenic patients showed significantly increased thresholds of WP and TPO relative to healthy controls. Antipsychotics did not alter pain thresholds. We found no correlation between pain perception and psychometric scales. Our findings demonstrate altered warmth and heat pain perception in acute schizophrenia. We believe that our findings can be attributed to information-processing abnormalities of the disorder and that they are not specific to pain processing, per se, since both WP and TPO were significantly different. Future studies should evaluate attentional deficits in schizophrenia in relation to pain perception.     

Visual perception and working memory in schizotypal personality disorder

OBJECTIVE: Patients affected by schizophrenia show deficits in both visual perception and working memory. The authors tested early-stage vision and working memory in subjects with schizotypal personality disorder, which has been biologically associated with schizophrenia. METHOD: Eleven subjects who met DSM-III-R criteria for schizotypal personality disorder and 12 normal comparison subjects were evaluated. Performance thresholds were obtained for tests of visual discrimination and working memory. Both form and trajectory processing were evaluated for each task. RESULTS: Subjects with schizotypal personality disorder showed intact discrimination of form and trajectory but were impaired on working memory tasks. CONCLUSIONS: These data suggest that subjects with schizotypal personality disorder, unlike patients affected by schizophrenia, have relatively intact visual perception. Subjects with schizotypal personality disorder do show specific deficits on tasks of comparable difficulty when working memory demands are imposed. Schizotypal personality disorder may be associated with a more specific visual processing deficit than schizophrenia, possibly reflecting disruption of frontal lobe systems subserving visual working memory operations.     

Do the siblings of schizophrenia patients demonstrate affect perception deficits?

Affect perception deficits have been extensively documented in schizophrenia and are associated with the social dysfunction that is characteristic of this disorder. The two previous studies examined facial affect perception in genetically at-risk samples and yielded mixed results. The current study was designed to provide a rigorous test of affect perception abilities among schizophrenia patients (n=58), their biological siblings without psychosis (n=51), and nonpsychiatric controls (n=49). Participants completed three measures of affect perception, including facial, vocal, and combined modality. Schizophrenia patients performed significantly worse than controls on two of the three affect perception tests as well as a composite index based on all three tests. The performance of the sibling group fell between the patient and control groups on each of the affect perception tests. However, group differences achieved statistical significance only for the composite index with the siblings performing significantly worse than controls and significantly better than the schizophrenia group. These findings demonstrate that subtle deficits in affect perception are detectable in the unaffected siblings of schizophrenia patients when multiple measures of different types of affect perception abilities are used in combination.     

Impaired emotion perception in schizophrenia: a differential deficit

We investigated previously reported contradictory findings regarding the nature of deficits in emotion perception among patients with schizophrenia. Some studies have concluded that such deficits are due to a generalized impairment in visual processing of faces, while others have found it to be restricted to facial emotional expressions. We examined 37 patients and 32 healthy controls, matched on age and education, using three computerized tests: matching facial identity, matching facial emotional expressions, and discrimination of subtle differences in the valence of facial emotional expressions. Our results showed impaired matching of emotions in patients with schizophrenia. This impairment did not manifest on tasks that depended on perceiving the identity of faces or cues of the relative valence of facial emotional expressions. Our findings support the differential deficit hypothesis of emotion perception in schizophrenia.     

Direction-selective motion blindness after unilateral posterior brain damage

Motion blindness (MB) is defined as the selective disturbance of visual motion perception despite intact perception of other features of the visual scene. MB is characterized by a pandirectional deficit of motion direction discrimination and is assumed to result from damage to the visual motion pathway, especially area MT/V5. However, the most characteristic feature of primate MT/V5 neurons is not their motion selectivity but their preference for one direction of motion (direction selectivity), which changes incrementally at neighbouring columns. In addition to this microscopic directional organization, studies in nonhuman and human primates suggest that single directions of motion are also coded at a more macroscopic level. We thus hypothesized that if MB in humans results from damage to direction-selective neurons in the visual motion pathway, posterior brain damage might cause MB which is direction selective, not pandirectional. The present study investigated motion direction discrimination in patients with posterior unilateral brain damage and determined separate psychophysical thresholds for the four cardinal directions. In addition, we analysed whether the direction of erroneous motion perception (i.e. the perception of right motion for upward motion) was random or showed a directional bias. We report three principal findings. First, motion direction discrimination was severely impaired in one or two directions while it was normal in the other directions. This constituted direction-selective MB. Second, MB was characterized not only by a quantitative direction-selective increase in psychophysical thresholds but also by a qualitative impairment of perceiving motion direction systematically in wrong directions. Both findings suggest that the cortical modules specialized for the perception of a single direction of motion might be larger than previously thought. Third, lesion analysis showed that unilateral damage, not only the human homologue of MT/V5 but also to parieto-occipital cortex, leads to MB.     

Visual processing and neuropsychological function in schizophrenia and schizoaffective disorder

Persons with schizophrenia and schizoaffective disorder exhibit deficits in both visual processing and neuropsychological tasks. Little is known, however, about whether these deficits are related to one another. We administered psychophysical tests of visual discrimination and recognition, and neuropsychological tests of abstract flexibility, verbal learning, visual memory, working memory and attention to 42 outpatients with stable but chronic schizophrenia or schizoaffective disorder. Multiple regression analyses were performed to determine the relationship between these measures of neuropsychological function and visual psychophysical performance. Results indicated that motion perception was associated with working memory, and that the addition of a memory component to motion perception (motion recognition) was associated with both working memory and visual memory. Visual performance was not associated with symptom severity as measured by the PANSS. These results suggest that psychophysical tests of visual processing may contribute to deficits on neuropsychological tests of visual cognition, and may also reflect cross-modal disturbances of working memory function.     

Face and body perception in schizophrenia: A configural processing deficit?

Face and body perception rely on common processing mechanisms and activate similar but not identical brain networks. Patients with schizophrenia show impaired face perception, and the present study addressed for the first time body perception in this group. Seventeen patients diagnosed with schizophrenia or schizoaffective disorder were compared to 17 healthy controls on standardized tests assessing basic face perception skills (identity discrimination, memory for faces, recognition of facial affect). A matching-to-sample task including emotional and neutral faces, bodies and cars either in an upright or in an inverted position was administered to assess potential category-specific performance deficits and impairments of configural processing. Relative to healthy controls, schizophrenia patients showed poorer performance on the tasks assessing face perception skills. In the matching-to-sample task, they also responded more slowly and less accurately than controls, regardless of the stimulus category. Accuracy analysis showed significant inversion effects for faces and bodies across groups, reflecting configural processing mechanisms; however reaction time analysis indicated evidence of reduced inversion effects regardless of category in schizophrenia patients. The magnitude of the inversion effects was not related to clinical symptoms. Overall, the data point towards reduced configural processing, not only for faces but also for bodies and cars in individuals with schizophrenia.     

Perception of faces in schizophrenia: Subjective (self-report) vs. objective (psychophysics) assessments

ObjectivesFace perception impairment in schizophrenia has been demonstrated, mostly through experimental studies. How this laboratory-defined behavioral impairment is associated with patients’ perceptual experience of various faces in everyday life is however unclear. This question is important because a first-person account of face perception has direct consequences on social functioning of patients. In this study, we adapted and administered a self-reported questionnaire on narrative perceptual experience of faces along with psychophysical assessments of face perception in schizophrenia.MethodsThe self-reported questionnaire includes six rating items of face-related functioning in everyday life, providing a subjective measure of face perception. The psychophysical assessment determines perceptual threshold for discriminating different facial identities, providing an objective measure of face perception.ResultsCompared to controls (n = 25), patients (n = 35) showed significantly lower scores (worse performance) in the subjective assessment and significantly higher thresholds (worse performance) in the objective assessment. The subjective and objective face perception assessments were moderately correlated in controls but not in patients. The subjective face perception assessments were significantly correlated with measurements of a social cognitive ability (Theory of Mind), again in controls but not in patients.ConclusionThese results suggest that in schizophrenia the quality of face-related functioning in everyday life is degraded and the role that basic face discrimination capacity plays in face-related everyday functioning is disrupted.     

Development of visual motion perception in children of patients with schizophrenia and bipolar disorder: a follow-up study

The "dorsal-stream vulnerability" hypothesis claims that motion-sensitive areas in the dorsal occipito-parietal visual system are vulnerable to genetic and environmental factors which affect brain maturation and development. The aim of this study was to investigate the possibility that developmental anomalies of directional motion perception can be detected in children of mothers with schizophrenia and bipolar disorder. Motion and form coherence thresholds were measured in 36 children of mothers with schizophrenia, 28 children of mothers with bipolar disorder, and 30 children with negative family history at 7, 8-9, and 10-11 years of age. These tasks require the detection of direction of coherently moving dots embedded among randomly oscillating dots (motion task) and the detection of tangentially oriented line-segments embedded among randomly oriented segments (form task). Results revealed that the rate of development in the motion task was less pronounced in children of mothers with schizophrenia than that in children of mothers with bipolar disorder and in age-matched controls. The development of form perception was spared. Children of mothers with bipolar disorder showed an intact development in both motion and form perception tasks. These results suggest that the progressive developmental abnormality of motion-sensitive visual areas may be a characteristic feature of schizophrenia-vulnerability.     

Psychophysical correlates of global motion processing in the aging visual system: a critical review

The consequences of visual decline in aging have a fundamental and wide-reaching impact on age-related quality of life. It is of concern therefore that evidence suggests that normal aging is accompanied by impairments in the ability to effectively encode global motion. Global motion perception is a fundamentally important process. It enables us to determine the overall velocity of spatially extensive objects in the world and provides us with information about our own body movements. Here, we review what is currently known about the effects of age on performance for encoding the global motion information available in random dot kinematograms (RDKs), a class of stimuli widely used to probe the mechanisms underlying motion perception. We conclude that age-related deficits in global motion perception are not all encompassing. Rather, they appear to be specific to certain stimulus conditions. We also examine evidence for an interaction between age and gender and consider the efficacy of techniques such as visual perceptual learning that may attenuate some of the visual deficits in the older adult population.