Abstract
Although many neurons in the primary visual cortex (V1) of primates are direction selective1, they provide ambiguous information about the direction of motion of a stimulus2,3. There is evidence that one of the ways in which the visual system resolves this ambiguity is by computing, from the responses of V1 neurons, velocity components in two or more spatial orientations and then combining these velocity components2,3,4,5,6,7,8,9. Here I consider another potential neural mechanism for determining motion direction. When a localized image feature moves fast enough, it should become smeared in space owing to temporal integration in the visual system, creating a spatial signalâa âmotion streakââoriented in the direction of the motion. The orientation masking and adaptation experiments reported here show that these spatial signals for motion direction exist in the human visual system for feature speeds above about 1 feature width per 100âms. Computer simulations show that this psychophysical finding is consistent with the known response properties of V1 neurons, and that these spatial signals, when appropriately processed, are sufficient to determine motion direction in natural images.
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Acknowledgements
I thank B. Henning for pointing out the potential value of orientation masking in this context. D. Albrecht, L. Cormack and B. Henning provided helpful discussions as well as comments on the manuscript. Supported by the National Eye Institute, NIH.
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Geisler, W. Motion streaks provide a spatial code for motion direction. Nature 400, 65â69 (1999). https://doi.org/10.1038/21886
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DOI: https://doi.org/10.1038/21886