Visual field defects for unidirectional and oscillatory motion in depth.

Visual fields for oscillatory motion in depth were recorded for 21 subjects. Near fields were different from far fields in 8 and similar in 11 subjects. Visual fields for unidirectional motion in depth were recorded for 16 subjects for near and far disparities. Some subjects had fields that differed for approaching versus receding motion in depth and/or for near versus far disparities. In particular, for near disparities, approaching versus receding motion gave fields that were different in 5 and similar 7 subjects; for far disparities, approaching versus receding motion gave fields that were different in 1 and similar in 10 subjects. For approaching motion in depth, near fields differed from far fields in 3 and were similar in 8 subjects; for receding motion in depth, near fields were different from far fields in 5 and similar in 8 subjects. Because sensitivity to monocular frontal plane motion showed no irregularities corresponding to the stereomotion field defects, we conclude that (1) stereomotion field defects were chiefly due to defective cortical processing of motion. We also conclude that (2) stereomotion field defects--at least for unidirectional motion--are caused by loss of sensitivity to unidirectional motion in depth rather than to abnormal interactions between mechanisms for approaching and receding motion, and (3) the finding of directional-specific stereomotion blindness is better explained by the two-population than by the one-population hypothesis of stereomotion blindness. We suggest that the substantial incidence of stereomotion field defects in normally-sighted subjects has implications for clinical studies and for visual assessment of pilots.