A stereo field map with implications for disparity processing.

The neural basis for stereopsis may be divided into at least two components: one mechanism that processes divergent disparities and a second mechanism that processes convergent disparities. The most clearcut evidence for the presence of these two components is the finding that some individuals lack either one or the other. However, when the ability to process both convergent and divergent disparities is present in the same individual it is more difficult to demonstrate the presence of two separate mechanisms. In this paper, the mechanisms for stereopsis are shown to consist of at least two components in the same individual. This demonstration is based upon a new kind of perimetry whereby field maps for stereopsis are plotted for both convergent and divergent disparities. Extensive measurements on one observer show that the zone of the visual field over which convergent disparities are processed may differ quite distinctively from the zone of the visual field over which divergent disparities are processed.