The effect of peripheral visual motion on focal contrast sensitivity in positive- and negative-symptom schizophrenia.

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.