Binocular interaction and depth sensitivity in striate and prestriate cortex of behaving rhesus monkey.

2. Impulse activity was recorded from neurons in fovea1 striate (A17) and prestriate (Al@ cortex of monkeys trained to fixate monocularly and binocularly by rewarding them for detecting an abrupt change in the intensity of a small luminous spot. During periods of fixation, single bright or dark narrow bars moving across a frontoparallel plane were presented at a series of different depths. 2. Nearly all cortical neurons studied received input from both eyes. Binocular neurons were classifiedLint two categories on the basis of their monocular responses: those that gave similar responses to stimulation of right and left eye (ocular balance) and those that gave different responses (ocular unbalance). Different kinds of binocular interactions were observed. 3. Most neurons (84%) were sensitive to location of the stimulus in depth. Four types of depth-sensitive cells were recognized: a) tuned excitatory neurons, the most common type, that gave excitatory responses over a narrow range of depth about the fixation distance often with inhibitory flanks nearer and farther, and that typically received a balanced binocular input; b) tuned inhibitory neurons whose responses were largely suppressed by stimuli at or close to the plane of fixation; c) near neurons, which responded well to stimuli in front of the fixation plane and were suppressed by those behind it; d) far neurons, the opposite of near neurons. The last three types of depth cells were usually ocularly unbalanced. Peaks and steps of depthsensitivity profiles occurred at or close to the fixation distance (within t 0.4O of disparity), whereas the total range of binocular interaction, even for a single cell, could extend to more than t lo of disparity. 4. The results suggest that there are cells in fovea1 striate and prestriate which may be part of