Figure 4. Schematic Depiction of “Barber Diamond” Stimuli Used to Study the Influence of Context on Perceived Motion and Its Neuronal Correlates.

(A) Stimuli consisted of a moving pattern of vertical stripes framed by a static, diamond-shaped aperture. The striped pattern itself was placed in the plane of ocular fixation while four textured panels that defined the aperture were independently positioned in depth using binocular disparity cues. The striped pattern was moved either leftward or right ward on each trial. Each of the four stimulus conditions used was a unique conjunction of direction of motion (right versus left motion of the striped pattern) and depth-ordering configuration. The two conditions illustrated (B and C) were created using a rightward moving pattern of stripes; two additional conditions (not shown) were created using leftward moving stripes. Near and Far identify the depth-ordering of the textured panels relative to the depth plane of the striped pattern.

(B) Upper-right and lower-left panels were placed in the Near depth plane, while the upper-left and lower-right panels were in the Far depth plane. Line terminators formed at the boundary of Near surfaces and the striped pattern are classified as extrinsic features resulting from occlusion, and the striped pattern is perceived to extend behind the Near surface. (Note that the gray stripes in this illustration are not part of the stimulus and are used solely to illustrate perceptual completion.) Conversely, line terminators formed at the boundary of the Far surfaces and the striped pattern are classified as intrinsic: they appear to result from the physical termination of the surface upon which the stripes are “painted.” As a result of this depth-ordering manipulation and ensuing feature interpretation, observers typically perceive the moving pattern of stripes in (B) as belonging to a surface that slides behind the Near panels and across the Far panels (to the upper-right). This direction is identified with motions of intrinsic terminators.

(C) The condition shown contains the same rightward motion of the pattern of stripes, but employs the depth-ordering configuration that is complementary to (B). In this case, observers typically perceive the striped pattern as belonging to a surface that is drifting to the lower right.

(D) 3-D illustration of one depth-ordering configuration used for these experiments. The 3-D percept requires “free cross-fusing” of the left and right panels (such that the right eye is aimed at the left panel and the left aimed at the right). Those viewers capable of free fusing should perceive the 3-D layout of the stimulus. In practice, the central striped pattern also drifted leftward or rightward.

A demonstration of this depiction, with motion, is available at http://vcl-s.salk.edu/Research/Motion-Integration/.

Source: Robert O. Duncan, Thomas D. Albright, and Gene R. Stoner, “Occlusion and the Interpretation of Visual

Motion: Perceptual and Neuronal Effects of Context,” The Journal of Neuroscience 20 (2000): 5885–5897.