Stereopsis and binocularity in the squirrel monkey

The squirrel monkey lacks anatomically demonstrable ocular dominance columns, and physiologically it has an ocular dominance distribution in V1 that is very different from that of macaques, with far fewer cells that strongly favor one eye over the other. We tested an alert squirrel monkey for physiological responses to stereoscopic stimuli by measuring evoked potentials in response to cytclopean patterns generated in dynamic random-dot stereograms. The monkey showed evoked responses both to changes in disparity and to shifts between correlation and uncorrelation between the two eyes. This result strongly suggests that the squirrel monkey can detect stereoscopic depth, which in turn casts some doubt on the assumption that ocular dominance columns bear an important relation to stereopsis.