Abstract

Eye movement responses to dual targets provide insight into mechanisms of visual information acquisition. It was previously shown¹ that symmetric point targets stimulating both hemispheres require extra processing time compared to either a single or a dual unidirectional stimulus. These so-called bifurcating point stimuli reveal the existence of preferred lateral direction. We substantiate and refine these results incorporating the effects of eccentricity. In the case of a unidirectional dual target an absolute preference exists for the target closer to the fovea. Responses to asymmetric bihemifield stimuli show that the lateral direction preference is contingent on target eccentricities. Being close to the fovea enchances, whereas being away from the fovea inhibits, the preference level of the point target. If one of the points is delayed, the overall lateral, spatial, and temporal preferences determine the response direction. At large interpoint delays for which the second point is still the preferred one, the response time measured with respect to the onset of this target is much shorter than the average latency. We propose a stochastic model accounting for the temporal aspect of our observations. Each point stimulus is processed in a separate channel in two stages, the first providing a general intermediate output utilizable in the processing of any additional input. Interaction between opposite hemispheric channels results in longer response duration due to the second stage processing time. The model reproduces the timing of events in responses to dual targets.

© 1985 Optical Society of America