Inter-ocular velocity differences or disparity temporal
changes? A unifying approach to the detection of
motion-in-depth through phase-based disparity
measurements.

Fabio Solari, Silvio P. Sabatini, Gianluca Nicolussi and Giacomo M. Bisio
DIBE - University of Genoa, Via Opera Pia 11a, 16145 Genova, ITALY

There are at least two binocular cues that can be used to determine the motion
of an object toward or away from an observer (Harris and Watamaniuk 1995,
Vision Res. 35:885-896). First, the visual system might use binocular
combination of monocular velocity signals. Second, the motion-in-depth
signal could arise by the rate of change of retinal disparity. We suggest that at
architectural level, both cues rely upon the same monocular measures, if a
phase-based disparity encoding scheme is assumed (Fleet et al. 1996, Vision
Res. 36:1839-1857).
In this perspective, interocular velocity differences as well as disparity
measures provide the same information about motion-in-depth, when the rate
of change of retinal disparity is evaluated as a total temporal derivative
of the disparity.  The resulting operator relies upon spatiotemporal
differentials of the left and right retinal phases that can be approximated by
linear filtering operations with spatiotemporal receptive fields.  By using a
network model we postulate the generation of binocular motion-in-depth selective
cells as a hierarchical combination of monocular spatiotemporal subunits.
Relationships between these subunits and the measured properties of simple and
complex cells in the visual cortex (Ohzawa et al. 1997, Neuroreport 8:iii-xii)
are discussed. Extensive simulations of the model have been performed to
validate the approach.