[Contrast detection thresholds during their presentation in right and left hemifields of vision]

We measured contrast detection thresholds for thin black vertical bars (1 min of arc wide, 1 deg long) against a bright background, which were presented eccentrically at 4 deg to the left or right of fixation and flanked on one side by a subthreshold bar having the same dimensions. On each presentation, the stimulus randomly appeared in the left or right visual hemifield. The separation between the test and the flanks varied from 1 to 60-120 min of arc. Different subjects showed better performance in different hemifields. This preference was lost or changed to opposite in the course of training. The central excitatory areas are more or less symmetrical, but inhibitory areas reveal asymmetrical tendency: when flanked bars were more peripheral than the test line, the inhibitory areas were larger. Our results show absence of hemispheric specificity in the line detection task. We discuss the ways of stimulus description in fovea and periphery.