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Jenny Read, Lisa Jones, Candy Rowe, Claire Rind, Vivek Nityananda, Ghaith Tarawneh; The limits of apparent motion perception in the praying mantis. Journal of Vision 2018;18(10):349. doi: https://doi.org/10.1167/18.10.349.
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When a visual pattern is displaced in small jumps, if the jumps are small and close enough in time, we perceive the pattern as moving smoothly. As the jumps become larger, the apparent motion becomes choppy, until eventually, beyond the maximum displacement "Dmax", we cannot distinguish the direction of motion at all . In humans, Dmax increases with the size of the pattern elements . We repeated this experiment in the praying mantis, varying the size and jump interval so as to keep the mean speed constant at 12.5cm/s. The stimulus was a random chequerboard with 100% contrast, filling a CRT screen 7cm in front of the insect; the elements are the chequer squares. For small displacements, stimuli reliably elicited an optomotor response: the mantis moved in the direction of the displacement. As the displacement increased, the probability of an optomotor response fell to zero. We defined Dmax for a given element size as the displacement which elicited an optomotor response on 50% of trials. We found that in the praying mantis as in humans, the plot of Dmax against element size is a straight line on log axes. In mantises, Dmax increases roughly as the square root of element size. In humans, Dmax tends to become independent of element size for the smallest elements. This is believed to reflect the scale of spatial filtering before motion extraction . In mantises, no such limit is observed: Dmax continues to decrease with element size down to the smallest values tested. We suggest this is because insect vision does not have a separate stage of spatial filtering which precedes motion extraction; rather, motion detection occurs at the earliest stages of insect vision. 1. Braddick (1974). Vision Research 14, 519-527 2. Morgan (1992). Nature 355 344-346
Meeting abstract presented at VSS 2018
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