When square wave gratings are viewed binocularly with lower luminance or contrast in one eye, the individual bars of the grating appear to rotate around a vertical axis (Venetian blind effect). The effect has typically been thought to occur due to retinal disparities that result from irradiation and, therefore, are entirely entoptic. If so, the visual system should process disparities from a luminance or contrast disparity and a geometric disparity at the same rate. Studies of motion-in-depth using geometric disparities have shown that the visual system is unable to process depth cues when those cues are oscillated at frequencies greater than 5 Hz. By changing contrast (experiments one and two) and geometric (experiment three) disparity cues over time, the present study measured the frequency at which both the perception of motion-in-depth and the perception of depth diminish. The perception of motion-in-depth from contrast disparities decreased near 1.1 Hz (experiments one and four) and the perception of depth from contrast disparities decreased near 1.3 Hz (experiments one, two and four); both of which are lower than the frequency where depth from a geometric disparity diminished (near 4.8 Hz in experiment three). The differences between the dynamics of depth from contrast and geometric disparities suggest that the perception arises from separate neural mechanisms.

When viewing reverspective stimuli, data-driven signals such as disparity, motion parallax, etc, help to recover veridical three-dimensional (3-D) shape. They compete against schema-driven influences such as experience with perspective, foreshortening, and other pictorial cues that favor the perception of an illusory depth inversion. We used three scaled-size versions of a reverspective to study the roles of retinal size, binocular disparity, and viewing distance--that influences both vergence and accommodation--in recovering the true 3-D shape. Experiment 1 used three conditions, in each of which a parameter was kept fixed across the three stimulus sizes: (a) fixed retinal size, (b) fixed viewing distance, (c) fixed disparity. The predominance of the veridical percept was recorded. Generally, the illusion strength was the same when the viewing distance was fixed, despite significantly different disparities and retinal sizes; conversely, illusion strength changed significantly in fixed-disparity and fixed-retinal-size conditions. Experiment 2 confirmed the results of experiment 1b (roughly equal performances for fixed viewing distance, independent of size) for two additional distances. Viewing distance and "scaled disparity" (disparity divided by retinal size) are good predictors of the data trends. We propose that disparity scaling is supported by both mathematical and 3-D shape considerations.

When a rectangular wave grating is binocularly viewed with a neutral density filter over one eye, an illusory rotation resembling that of a partially opened Venetian blind is perceived (Cibis and Haber, 1951). Using a binary classification task, in the first experiment, the probability of perceiving a rotation in a given direction was measured as a function of a factorial combination of inter-ocular contrast (see Note 1) and luminance ratios. The probability of a rotation in a given direction decreased monotonically with the luminance of the brighter bars when the grating contains a less than unity contrast. This result is inconsistent with (i) the model of the Venetian blind effect proposed by Cibis and Haber (1951), (ii) a mechanism based on irradiation with a compressive non-linearity (von Helmholtz, 1911/1924, pp. 186-193) and (iii) contemporary stereo-energy/cross-correlation models of stereopsis. In the second and third experiments, we tested the prediction that irradiation combined with an early compressive non-linearity in response implies a positive relationship between both the threshold contrast or average luminance disparity to perceive rotation and the magnitude of perceived rotation, and the blur width at the bar's edge. No support was found for the prediction. We propose an intensity difference model of the probability of perceiving a rotation in a given direction as a function of the interocular difference in luminance or contrast.

The present experiment was designed to examine the roles of painted linear perspective cues, and the convexity bias that are known to influence human observers’ perception of three-dimensional (3D) objects and scenes. Reverse-perspective stimuli were used to elicit a depth-inversion illusion, in which far points on the stimulus appear to be closer than near points and vice versa, with a 2 (Type of stimulus) × 2 (Fixation mark position) design. To study perspective, two types of stimuli were used: a version with painted linear perspective cues and a version with blank (unpainted) surfaces. To examine the role of convexity, two locations were used for the fixation mark: either in a locally convex or a locally concave part of each stimulus (painted and unpainted versions). Results indicated that the reverse-perspective illusion was stronger when the stimulus contained strong perspective cues and when observers fixated a locally concave region within the scene.