2D motion aliasing yielding 3D ambiguity. A study with variants of a necker cube

AbstractThe 2D projection of a rotating Necker cube yields an ambiguous 3D interpretation based on both 2D shape and kinetic depth information. The present study shows that the alternation rate of the two 3D interpretations is constant with the rotation speed up to some critical value (around 25 turns/min for a cube whose sides subtend 2.5 deg) and increases monotonically thereafter. It is proposed that the additional perceptual reversals (PRs) observed at high rotation speeds are due to the increased frequency of the crossovers of the cube's edges. These crossovers yield 2D motion “aliasing” (or discontinuity) and “veridical” (or continuity) motion components. The motion aliasing (or crossover) hypothesis states that, in addition to the inherent ambiguity of the dynamic 2D projection of 3D objects, perceptual motion/perspective reversals will occur any time the discontinuity speed takes over the continuity speed. It is proposed that the relative strengths of the two components depend on the linear speed of the projected edges and that the discontinuity components take over the continuity one in the speed range where contrast sensitivity (or, above threshold, efficiency) is a decreasing function of speed. The motion aliasing hypothesis was tested and supported in a series of independent experiments showing that, for rotation speeds higher than 25 turns/min the PR rate increases with the crossover frequency at a constant speed, with linear speed at a constant crossover frequency and with the similarity of the crossing bars in terms of their orientation, polarity and spatial overlap. In addition, some of these experiments suggest that 2D shape and kinetic depth 3D-cues combine in such a way that the average PR rate they yield together is the same as the PR rate yielded by each of them independently. In the Discussion section we elaborate on issues related to the perceptual combination of ambiguous shape and kinetic depth, 3D cues

Binocular rivalry with isoluminant stimuli visible only via short-wavelength-sensitive cones

To test whether the binocular contour rivalry mechanism is tritanopic, we presented isoluminant, rival stimuli visible only via the short-wavelength-sensitive (S) cones, We stimulated only the S cones with violet gratings superimposed on a bright yellow field that adapted the responses of the middle- and long-wavelength-sensitive (M and L) cones, We found that an S-cone grating presented to one eye rivalled with an orthogonal grating presented to the other, Rivalry persisted over a range of luminances and contrasts of the S-cone stimuli, and was greater than could be accounted for by nonrival fading, The spatial spread of rivalry from S-cone stimuli is similar to that for the same stimuli when visible also to the M and L cones (luminance stimuli). We found that an S-cone stimulus would rival with a luminance stimulus, and exploited this to determine the equivalent luminance contrast of S-cone stimuli by putting them in a rivalry competition with luminance stimuli, For rivalry, the equivalent luminance contrast of isoluminant, S-cone stimuli is much less than their S-cone contrast. The existence of rivalry with isoluminant stimuli, along with earlier evidence that such stimuli can support stereopsis, challenges the view that an achromatic channel alone drives certain higher level functions such as depth perception