Perception of complex motion in humans and pigeons (Columba livia)
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In the primate visual system, local motion signals are pooled to create a global motion percept. Like primates, many birds are highly dependent on vision for their survival, yet relatively little is known about motion perception in birds. We used random-dot stimuli to investigate pigeons’ ability to detect complex motion (radial, rotation, and spiral) compared to humans. Our human participants had a significantly lower threshold for rotational and radial motion when compared to spiral motion. The data from the pigeons, however, showed that the pigeons were most sensitive to rotational motion and least sensitive to radial motion, while sensitivity for spiral motion was intermediate. We followed up the pigeon results with an investigation of the effect of display aperture shape for rotational motion and velocity gradient for radial motion. We found no effect of shape of the aperture on thresholds, but did observe that radial motion containing accelerating dots improved thresholds. However, this improvement did not reach the thresholds levels observed for rotational motion. In sum, our experiments demonstrate that the pooling mechanism in the pigeon motion system is most efficient for rotation.
KeywordsVisual perception Motion perception Columba livia Coherence threshold Motion integration
We would like to thank J.P., A.N.S. and M.K.M. for participating in our study. We would also like to thank Isaac Lank, Jeffrey Pisklak, and Jason Long for their help with technical issues and for running the pigeons in the experiments. This research was supported by grants from the National Science and Engineering Research Council (NSERC) of Canada to M.L.S. and D.R.W., and by an NSERC Alexander Graham Bell Canada Graduate Scholarship (Doctoral level) to C.R.M.
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