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Eric Hiris, Aurore Krebeck, Jennifer Edmonds, Alexandra Stout; What learning to see the motion of nothing in particular tells us about biological motion perception. Journal of Vision 2004;4(8):234. doi: https://doi.org/10.1167/4.8.234.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Biological motion is often considered a special type of motion. We sought to determine if individuals could learn to perceive arbitrary motion as well as they perceive biological motion. Method: Participants viewed arbitrary motion embedded in spatially randomized masks. Arbitrary motion was created by systematically changing the location of the motion associated with a point light walker. Each of the four participants had their own version of arbitrary motion; half were based on the motion of upright walkers and half were based on the motion of inverted walkers. Participants completed multiple blocks of 100 trials over many days in an attempt to learn their particular arbitrary motion stimulus. Results: Depending on the participant, detectability (as measured by d′) increased abruptly after 6 to 13 blocks. Changing the ‘facing’ or inverting the arbitrary motion did not have any systematic effects on detectability. This effect is unlike biological motion, which is sensitive to inversion. Additional observations were made where participants had to indicate whether or not the top and bottom half of the stimulus were coherent (that is, had the same ‘facing’) or not. In this case, participants were able to indicate the coherence of regular point light walkers, but could not do so for arbitrary motion stimuli. Conclusions: Participants can learn to detect arbitrary motion stimuli after extended experience with the stimuli. However, given that they could not make reliable coherence judgments, participants are not basing their detection on perceiving the entire stimulus. Compared to arbitrary motion, biological motion enjoys an advantage in perceptual processing which is likely based on form cues that are available only in the biological motion stimuli.
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