![]() Hence, regardless of the surround disparity, this neuron preferred a centre that was positioned in front of the surround. Positioning the surround þ0.48 behind the fixation plane, moves the tuning curve to the right by a similar amount. When the surround was moved to a position 20.48 in front of the fixation plane (open circular symbols), the tuning curve to the centre stimulus moved by approximately the same amount to the left. (d ) This V4 neuron preferred a nearby centre (negative/ crossed disparities) when the surround was placed at the plane of fixation (filled rectangular symbols). If neurons are tuned to the relative disparity between the centre and surrounding stimulus, their tuning curves should shift by the same amount as that of the applied surround disparity. One can then manipulate the disparity of the circular centre stimulus, which brings the centre stimulus to the front or the back of the fixation plane. For example, a surrounding annulus can be placed in front of, behind or at the fixation plane. (Figure adapted with permission from Parker and Tanabe et al.) (c) In experiments wherein the relative disparity tunings of neurons are examined, stimuli with relative disparities are placed at different positions in depth with respect to the fixation plane. The V4 neuron, however, is only weakly tuned to the disparity of the dots in the anti-correlated random-dot stereogram. The V1 neuron is still markedly tuned to the disparity in anti-correlated stereograms. The stimuli used in these studies were similar to those shown in (a). (b) Average responses of a V1 neuron (left panel) and a V4 neuron (right panel) to correlated (black filled symbols) and anti-correlated (white open symbols) random-dot stereograms with different disparities (x-axis). In contrast to correlated random-dot stereograms, free-fusing the leftmost and rightmost dot pattern does not elicit the percept of a circular patch protruding from a background. The rightmost two random-dot stereograms are anti-correlated: the dots in both images are located at exactly the same positions, and thus have exactly the same disparities with the leftmost dot pattern, but the contrast polarity of the corresponding dots in each figure has been reversed: white dots in the middle figure are black in the right figure, and vice versa. Free-fusing these images led to the percept of a circular patch protruding from a background. corresponding dots in the left and middle image have the same colour. (a) The leftmost two random-dot stereograms are correlated, i.e. The results are discussed in terms of the importance of the particular type of stimulus used in the learning process and in terms of perceptual learning and attention.Responses to anti-correlated random-dot stereograms and to relative disparity. Finally, in experiment 6 it was shown that depth edges are learned when the internal depth regions of the stereogram are ambiguous. It was shown in experiment 4 that the depth edges of random-dot stereograms are not learned, whereas the results of experiment 5 indicate that the internal depth regions are learned. In the second set of experiments the learning of two binocular surface properties of random-dot stereograms, depth edges and internal depth regions, was investigated. This result indicates that the traditional belief that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered. In experiments 2 and 3 evidence was obtained that suggests that observers can learn, to a certain degree, monocular random-dot patterns and that this learning facilitates the depth percept. In experiment 1 the retinal position-specific learning effect was reproduced and in a follow-up experiment it was shown that the position specificity of learning can be accounted for by selective visual attention. In the present study some specific properties of the learning effects reported for random-dot stereograms are examined. Learning to See Random-Dot Stereograms Learning to See Random-Dot Stereograms
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