Oscillatory depth as a function of temporal frequency

The percept of oscillatory motion in depth was generated by a luminance modulation of a sinusoidal nature induced within each dot pair of a stationary random assembly of paired dots. The dots were miniature sources of polarized light viewed through a rotating ocular polarizer, which facilitated both the percept of oscillations and the modulation of luminance at any desired frequency. Depth responses were studied as a function of frequency within the 0-2 Hz range. A strong amplitude decrease was noticed at a mean frequency of f(1)=0.81 Hz; oscillations were perceived as 'rectified' for f > f(1) with an additional minimum of crossed-disparity depth at f(2)=1.60 Hz. It is suggested that the intensity modulation of the light beams mapping the stationary stimuli onto the retinae was a likely factor responsible for the observed depth minima and the rectification of faster oscillations. Results are compared to those obtained in a traditional setting, where the percept of oscillations in depth had been generated by disparity variations due to lateral motion of the stimuli.