THE AREA OF SPATIAL INTEGRATION FOR INITIAL HORIZONTAL DISPARITY VERGENCE

We investigated over what central area disparity in a random dot stere ogram is integrated to stimulate an initial vergence response, Vergenc e was measured subjectively, with a forced choice dichoptic nonius ver nier task following a brief (230 msec) stimulus presentation. Stimuli were random-dot stereograms showing a central circular disc of 12.5 mi n are crossed retinal disparity in front of, and occluding, a same den sity fixation plane surround, The size of the disc was varied, All ten observers responded to the brief stimulus. Initial vergence increased with increasing disc diameter and, for nine out of ten subjects, reac hed a maximum with the disc ca 6 deg, suggesting this is the extent of the spatial integration region. Below 6 deg diameter, surround and ta rget disparities were averaged together, Initial horizontal vergence r esponds automatically to a cyclopean target presented in the centre of gaze by pooling disparities within a limited but surprisingly large a rea. (C) 1998 Elsevier Science Ltd.