Parallel processing of binocular disparity in the cat's retinogeniculocortical pathways

In the cat, parallel streams of information processing have been traced from X-, Y- and W-type retinal ganglion cells to visual cortical areas 17 (X-, Y- and W-type), 18 (Y-type) and 19 (W-type). In the present study we have examined, in the anaesthetized and paralysed adult cat, the role played by X-, Y- and W-subsystems, projecting to areas 17 and 19, in the processing of binocular retinal disparity. The tapetal reflection technique was used to monitor residual eye movements and to provide a map, for each eye, of the retinal blood vessels which could later be compared with retinal wholemounts stained with cresyl violet to reveal the area centralis. The receptive-field disparities of cells recorded from areas 17 and 19 were compared with each other and with reference to the visual axes defined by the area centralis of each eye. Cells of area 19 (receiving W-type input) had horizontal receptive-field disparities that were significantly more divergent than those of the cells in area 17 and 17–18 ‘border region’. Referred to the area centralis, the mean horizontal receptive-field disparity in area 19 was –0.5°( ± 0.8°). The mean horizontal receptive-field disparity of area 17 (receiving X-, Y- and W-type input) was convergent with respect to the visual axis at +2° (± 0.5°). Finally, the mean horizontal receptive-field disparity of the cells in the 17–18 border region (which receive mainly Y -type input) was even more convergent (2.6° ± 1.5°) than that of area 17. Binocular interactions of cortical neurons were tested with the Risley biprism technique. Area 19 cells had maximal responses to binocular stimulation when the receptive-field disparities were either close to zero or slightly divergent. In contrast, area 17 cells tended to respond optimally to disparities that were either slightly or strongly convergent. At the level of the lateral geniculate nucleus there were significant differences between the receptive-field disparities inferred from the comparison of receptive-field positions of adjacent neurons recorded on either side of the border between the A and A1 geniculate laminae and those inferred from a similar comparison at the C1–C2 border. The mean horizontal disparities inferred from the interlaminar comparison at the A–A1 border were +2.1° (±0.3°); those inferred from the interlaminar comparison at the C1–C2 border –0.2 (± 0.2°) were more divergent. This difference is consistent with the idea that there is a subclass of W-type ganglion cells pro