title: The effect of peripheral visual motion on focal contrast sensitivity in positive- and negative-symptom schizophrenia.
abstract: The aim of the present research was to investigate the effect of peripheral (ambient) stimulation on focal visual processing using the far-out jerk effect in normal observers and subgroups with positive- and negative-symptoms in schizophrenia. The far-out jerk effect refers to a reduction in sensitivity of a briefly presented stimulus in central vision in the presence of a sudden movement or oscillation of a stimulus in peripheral vision. In order to measure the far-out jerk effect the focal contrast sensitivity of 5.0Hz modulated sinusoidal target gratings (0.5, 1.0, 2.0, 4.0, and 8.0 number of cycles per degree (c/degrees )) was measured in the presence of three kinds of peripheral surround: a blank field, a stationary 0.75 c/degrees grating, and a 5.0Hz drifting 0.75 c/degrees grating (far-out jerk effect). The findings showed that there were no significant differences in focal contrast sensitivity between the control and positive-symptom group with a blank field and stationary grating surround. However, a 5.0Hz drifting grating surround resulted in a significant reduction in contrast sensitivity at 0.5, 1.0 and 2.0 c/degrees in the positive-symptom group. In comparison with the control group the negative-symptom group showed a generalised reduction in focal contrast sensitivity, a significantly smaller far-out jerk effect, and a significant reduction in contrast sensitivity at 0.5 c/degrees with a stationary grating surround. The finding that both stationary and moving peripheral surrounds have an inhibitory effect on focal contrast sensitivity suggests that there is a dispersion in the visual demarcation between stationary and temporal events in the perception of visual motion in the negative-symptom group.
authors.affiliation: School of Psychology, University of Tasmania, G.P.O. Box 252C-30, Hobart, Tasmania 7001, Australia. walter.slaghuis@utas.edu.au
authors.forename: Walter L
authors.initials: WL
authors.lastname: Slaghuis
authors.forename: Alanda K
authors.initials: AK
authors.lastname: Thompson
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity; D005260:Female; D005425:Flicker Fusion; D006801:Humans; D008297:Male; D009039:Motion Perception; D010364:Pattern Recognition, Visual; D010470:Perceptual Masking; D010775:Photic Stimulation; D011569:Psychiatric Status Rating Scales; D011601:Psychophysics / Q000379:methods; D012559:Schizophrenia / Q000145:classification / Q000503:physiopathology*; D012565:Schizophrenic Psychology; D013028:Space Perception / Q000502:physiology; D014787:Vision Tests; D014794:Visual Fields