The size of antagonistic centre-surround motion mechanisms decreases with increasing spatial frequency I Serrano-Pedraza1, M Gamonoso-Cruz1, V Sierra-Vázquez1, A M Derrington2 |
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1Faculty of Psychology, Universidad Complutense de Madrid, Spain |
| Human ability to discriminate motion direction of a Gabor patch diminishes with increasing size and contrast. This result has been explained by center-surround antagonism in motion sensors. We are interested in the size of motion sensors tuned to different spatial frequencies. Using Bayesian staircases, we measured duration thresholds of 5 subjects in a motion-direction discrimination task using vertically oriented gratings moving at 2 deg/sec, and presented with high contrast (46%) in the centre of the screen. We tested three spatial frequencies, 1 c/deg, 3 c/deg, and 5 c/deg, and six Butterworth-window diameters within the range 0.2 to 12 deg (depending on the spatial frequency). At each spatial frequency, duration thresholds increase with increasing size and stabilize when the size of the spatial window reaches a certain size. The size at which the duration thresholds stabilize gives an indication of the diameter of the suppressive surround. This diameter decreases approximately from 10 to 3 deg with increasing spatial frequency. These sizes are similar to the receptive-field sizes (at 0 deg retinal eccentricity) of neurons in the visual area MT. [Supported by Grant No. PSI2011-24491 from Ministerio de Ciencia e Innovación (Spain)] |
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