Abstract

This psychophysical study explored one possible basis for visually judging the direction of motion in depth. We propose that the changing-size channels precisely compute the algebraic difference between the velocities of opposite edges of a target, thus extracting the velocity component V_z along a line through the eye independent of the trajectory of the target, so that (with added “jitter”) this computation is accurately independent of the component of motion V_x parallel to the frontoparallel plane over a wide range of V_x:V_z ratios. We have no evidence for a complementary channel that computes V_x independently of V_z over any comparable range of V_x: V_z ratios. Our evidence shows that the oscillations of the edges of our stimulus square were equivalent to the oscillation of the square along one of 11 trajectories in depth. All 11 trajectories had the same value of V_z, but the 11 trajectories had different V_x values. In separate experiments, subjects adapted to each trajectory and we measured threshold elevations for two test oscillations, one equivalent to pure z-direction motion and the other equivalent to pure x-direction motion. To a first approximation, threshold elevations for the z-direction test were the same for all 11 trajectories, with the greatest departure from constancy (30%) when two edges of the adapting stimulus were stationary (i.e., equivalent to trajectories that just grazed the eye). Adding an 8-Hz “jitter” oscillation to the 2-Hz adapting oscillation “linearized” the visual response so that threshold elevations were rendered accurately constant (± 5%) for all trajectories tested.

© 1980 Optical Society of America

Motion sensitivity measured by a psychophysical linearizing technique

D. Regan and K. I. Beverley
J. Opt. Soc. Am. 71(8) 958-965 (1981)

Temporal selectivity of changing-size channels

K. I. Beverley and D. Regan
J. Opt. Soc. Am. 70(11) 1375-1377 (1980)

Motion and vision. III. Stabilized pattern adaptation

D. H. Kelly and Christina A. Burbeck
J. Opt. Soc. Am. 70(11) 1283-1289 (1980)

Pupil responses to foveal exchange of monochromatic lights

Rockefeller S. L. Young and Mathew Alpern
J. Opt. Soc. Am. 70(6) 697-706 (1980)

Phase selectivity of spatial frequency channels

Robert Michael Jones and Ulker Tulunay-Keesey
J. Opt. Soc. Am. 70(1) 66-70 (1980)