Biomedical subjects

Summer Sheremata

Publications and source records attributed to Summer Sheremata.

4 recordsLinked to original sources

PubMed2006

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.

Adolescent↗

PubMed2006

Increasing distractor strength improves accuracy.

Attention enhances task-relevant signals while filtering task-irrelevant signals; however, this selection process is not perfect. It is generally assumed that the stronger the irrelevant signal, the more strongly performance is disrupted. The effect of irrelevant coherent motion signals on performance on a color-discrimination task was systematically examined. Motion direction was either congruent or incongruent with response selection. Performance was most impaired when motion signal strength was just above perceptual threshold and improved when the motion signal strength increased. These results suggest that distractors of higher strength increase attentional modulation and are filtered before they interfere with task performance.

Adolescent↗

PubMed2004

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.

Adult↗

PubMed2003

Effects of typical, atypical, and no antipsychotic drugs on visual contrast detection in schizophrenia.

OBJECTIVE: Visual contrast detection has been reported in some studies to be normal in schizophrenia patients, but in other studies impairments have been reported. Because contrast detection in the visual processing system is mediated by dopamine, and because the pharmacotherapy of schizophrenia involves blocking dopamine postsynaptic receptor sites, the authors investigated the effects of dopamine-blocking antipsychotic drugs on visual contrast detection in schizophrenia. METHOD: Visual contrast detection thresholds were measured in healthy subjects and schizophrenia patients receiving typical and atypical antipsychotic drugs; a two-alternative, forced-choice psychophysical method was used. Also included were six patients receiving no antipsychotic treatment as well as clinically unaffected first-degree relatives of the schizophrenia patients. RESULTS: Patients receiving atypical antipsychotic drugs showed unimpaired visual contrast detection, those given typical antipsychotic drugs exhibited higher visual contrast detection thresholds, and the unmedicated schizophrenic patients showed visual contrast detection thresholds significantly below those of healthy subjects. CONCLUSIONS: Dopamine modulation via D(2) receptor blockade affects sensory processes in schizophrenia, shifting visual contrast detection from hypersensitivity in the unmedicated state to normal and even to hyposensitive levels. Thus, antipsychotic drug treatment may account for the inconsistent reports concerning visual contrast detection in schizophrenia.

Adult↗