Visual Perception of Optic Flow in the Left and in the Right Visual Hemifield

Abstract

Recently we have found right visual hemifield (HF) superiority in detection of local texture optic flow discontinuity (H O Levashova and O V Levashov, 1996 Perception25 Supplement, 128). In the present work we investigated a possible difference between hemifields in the perception of global optic flow. The stimulus consisted of two large texture fields which moved across the screen to the left and to the right from a central vertical line. It gave the illusion of motion through an infinite corridor with high walls. The left or the right wall could be curvilinear (convex) while the other one was flat. In order to make the task more difficult the central vertical meridian of the screen was occluded by a black mask with a width of 5 deg. The task of the subject was to detect the curvilinear wall and press the ‘left’ or the ‘right’ key in accordance with target position. When the target was absent (in some presentations both the walls were flat) or when the subject could not detect it he/she had to press the third key. The distance from the screen was 57 cm. One experimental session consisted of 100 – 150 trials. All subjects showed a superiority of the right hemifield (the difference was significant, p<0.05). The observed right-hemifield superiority in the detection of large texture flow could suggest that the left hemisphere has a certain dominance in visual perception of optic flow. This is in agreement with the hypothesis that the left hemisphere is more ‘phasic’ and the right hemisphere is more ‘tonic’ [O V Levashov, 1989 Computational Models of Sensory Systems (Moscow: VINITI) (in Russian)].