PubMed · 5867016
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R E Wienke, W C Steedman. 1965. Apparent motion in geometric depth.. https://doi.org/10.1177/001872086500700303
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Several aspects of the viewing situation affect the ability to determine heading from optical flow. These include the amount of depth variation and number of texture elements in the scene, the location and amount of the visual field stimulated, and the position of the focus of expansion within the stimulus. Without a quantification of the discrimination information provided by the stimuli presented to the observer, it is impossible to determine how much of an observed change in performance reflects the properties of neural mechanisms and strategies employed by the observer. To enable a better quantification, we developed an ideal observer for the discrimination of heading from random-dot flow fields. Internal noises of the ideal observer were set by the results of single-dot velocity discrimination experiments. We compared human and ideal observer performance in discriminating headings with different patterns of flow (e.g. radial vs laminar) presented on different parts of the retina. Efficiency--the ratio of ideal and human thresholds--was fairly constant for the various flow patterns and retinal eccentricities. This outcome indicates that most of the variation in human observers' ability to estimate heading from the flow patterns and retinal loci considered here is due to changes in the discrimination information provided by the stimulus after measurement by the visual system. In the discussion, we show how the ideal observer can be used to quantify the spatial distribution of heading discrimination information for any observer translation through any scene represented by dots.
The additivity assumption relates to the various stereo-disparity components in the vertical and horizontal meridians, each of which is assumed to be independent of the other, with the total disparity in each dimension being the linear sum of the separate components. Information about the position of the eyes provided by the corollary discharge leads to compensatory changes in the lateral geniculate nuclei whereby the angle of gaze disparity component at retinal level is offset by equal and opposite changes at geniculate level. These geniculate changes concern only eye position. Changes in the retinal images such as those produced by lenses (i.e. induced effect) are passed on to the cortex without modification at the geniculate level. Discrimination of the local depth disparity component can be achieved by subtracting the local vertical eccentricity component from the total horizontal disparity.
Perceived slant produced by size disparities in random-dot displays was measured by tactile matching. For a 60 deg surface, slant produced by vertical-size disparity (the induced effect) was opposite to that produced by horizontal-size disparity. Overall-size disparity produced a little slant. With small displays, effects of horizontal and vertical disparities were reduced but not those of overall disparity. A zero-disparity surround increased effects of horizontal and overall disparities but reduced the induced effect. A mixture of horizontally disparate and zero-disparity dots produced two slanted surfaces. Vertically disparate and zero-disparity dots produced one slanted surface. Abutting opposite horizontal disparities produced surfaces with a sharp boundary. Abutting vertical disparities produced surfaces with a gradual boundary. Perceived slant depends on the difference between horizontal-size disparity detected locally and mean vertical-size disparity over a relatively large area.