Asymmetries in the Control of Saccadic Eye Movements to Bifurcating Targets

Abstract

Abstract : The task of responding to one of two simultaneously presented targets often reveals unexpected yet profound preferences in the direction of saccadic eye movements. In the present investigation, a simple experimental paradigm was used in which a single point of light bifurcates symmetrically to the left and right of the fixation point. Under these conditions, most subjects show an eye movement response preference to either the left or right. The present data show that this preference can be eliminated by delaying the onset of the target, presented in the preferred direction, by about 40 milliseconds. This indicates that in the sequence of events occurring prior to the execution of a saccade, a window of time of this duration is allocated for decisions concerning direction, of response even when targets are presented to both visual hemifields. It was also found that the bifurcating targets interact to significantly increase response latencies in both the preferred and nonpreferred directions. Further, the interaction is asymmetrical, in that a target presented in the preferred direction has a greater effect that a target in the nonpreferred direction on responses in the counter direction. The results suggest an asymmetry in hemispheric interaction that has not previously been demonstrated in the visual-oculomotor system. Keywords: Target detection; target discrimination.