Abstract
This study investigated stereoscopic (cyclopean) motion in the frontoparallel plane measuring duration thresholds for different stimulus parameters: disparity, spatial frequency, temporal frequency, and stimulus size. To construct cyclopean motion, we used sinusoidal disparity corrugations obtained with random dots stereograms that changed every frame at 120 Hz for each eye. Thus, no luminance motion was present, only the disparity corrugation was moved. Using Bayesian adaptive staircases, we measured duration thresholds for detecting the correct direction of motion of horizontal (left-right) and vertical (up-down) sinusoidal corrugations. In the first experiment we tested the effect of disparity for 0.4c/deg drifting at 2 Hz. Duration thresholds decreased with increasing disparity until 200 arcsec then, thresholds remained constant. The other experiments were performed with disparities higher than 200arcsec. In the second experiment, we tested different temporal frequencies (range 0.5-4 Hz) for vertical and horizontal sinusoidal corrugations of 0.2 c/deg. Results show that duration thresholds decreased with increasing temporal frequency until 1-2 Hz and then remained constant. From 2 to 4 Hz, a strong anisotropy was present, where vertical corrugations showed higher duration thresholds than horizontal corrugations. In the third experiment, we tested the effect of size (from 8 to 22 deg) for two spatial frequencies, 0.2 and 0.4 c/deg drifting at 2 Hz. Results show that duration thresholds decreased with increasing size until 8 deg, then duration thresholds remained constant. Our results show, for the first time, a strong stereomotion anisotropy for temporal frequencies greater than 1 Hz and suprathreshold disparities. Our results also show that stereomotion behaves differently than luminance (first-order) motion when measuring duration thresholds. For example, for stereomotion, no surround suppression was found when comparing large and small sizes (we found facilitation); and also, increasing disparity showed lower duration thresholds that is the opposite result to increasing contrast in the luminance domain.