Motion-stereo mechanisms sensitive to inter-ocular phase.
We measured depth from interocular delay (The Pulfrich effect) using a dynamic random-dot pattern, consisting of a spatially-random noise field, the individual elements of which were sinusoidally-modulated in luminance over time. When an interocular phase difference in the flicker was introduced the display appeared to rotate in depth around a vertical axis like a transparent textured cylinder. The threshold phase lag was in the region of 5-10 degrees in different observers, which translated into a non-constant, decreasing interocular delay (ms) as the flicker frequency was increased. We conclude that phase, not delay, is the critical parameter in determining the detection of depth. Threshold signal/noise ratios were measured at different delays to determine the optimum phase difference, which was found to be in the region 60-90 degrees. However, delays centred around 180 degrees were less detectable than those around zero, ruling out a quadrature input to the stereo-motion mechanisms. We show that depth-from-phase is a natural consequence of paired monocularly motion-direction sensitive neurones. Complex energy-detecting neurones are not required to explain the findings.
Morgan
M J
MJ
Institute of Ophthalmology, University College London, Bath Street, London, UK. m.j.morgan@ucl.ac.uk
Fahle
M
M
D005583:Fourier Analysis; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D011594:Psychometrics; D012680:Sensitivity and Specificity; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D015348:Vision, Binocular / Q000502:physiology*