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Julian M Fernandez, Bart Farell; Diminished discriminability of motion in depth after adaptation to frontoparallel motion. Journal of Vision 2003;3(9):468. doi: https://doi.org/10.1167/3.9.468.
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© ARVO (1962-2015); The Authors (2016-present)
There are two possible binocular mechanisms for the detection of motion in depth (MID). One is based on disparity change over time and the other is based on inter-ocular velocity differences (IOVD). It has previously been shown that disparity change over time can produce the perception of MID. However, demonstrating the same for IOVD has proved elusive because of the difficulty for isolating this cue from disparity change (the inverse can easily be done). Thus, studying the contribution of IOVD to MID relies on indirect cues. Existing psychophysical and physiological data are inconclusive as to whether IOVD is used in primate vision. To study the contribution of IOVD to the perception of MID, we used motion adaptation. Adapting to frontoparallel motion can enhance speed discrimination or diminish it, depending on the adapting and test stimuli. If IOVD contributes to MID, we would expect that discriminability of the speed and direction of MID will be also affected after adaptation, because IOVD is basically a comparison between two monocular frontoparallel motion signals. In two experiments using random-dot stereograms, we compared discriminability with and without previous binocular adaptation to horizontal frontoparallel motion. The only difference between the adaptation and no-adaptation conditions was that in the latter the adapting motion was random instead of horizontal. In the first experiment we tested MID direction discrimination (approaching vs. receding). In the second experiment we tested MID speed discrimination along the line of sight. In both experiments we found that discriminability was lower after adaptation. No change was found in a disparity discriminability control test. We conclude that IOVD contributes to the perception of MID.
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