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Szonya Durant, Colin W. G. Clifford; Dynamics of centre-surround interactions in orientation perception. Journal of Vision 2005;5(8):231. doi: 10.1167/5.8.231.
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© ARVO (1962-2015); The Authors (2016-present)
Contextual effects abound in vision. For example, a vertical grating appears rotated away from a surrounding grating that is oriented at 15° to the vertical: the tilt illusion (TI). The orientation-selective nature of the TI is consistent with mediation by interactions within visual cortex. Here, we investigate the dynamics of these interactions by presenting centre and surround asynchronously. The test stimulus is a 1cpd sinusoidal grating presented in a 3° diameter circular aperture. The surround is a grating of the same spatial frequency oriented at ±15° to the vertical and presented in an annulus with an external diameter of 15°. Centre and surround are each presented in Gaussian temporal windows of 20ms full-width at half-height. Subjects report whether the central grating appears tilted clockwise or anti-clockwise from vertical. Subjective vertical is measured for ±15° surrounds using interleaved adaptive staircases. The magnitude of the TI is taken as half the difference between subjective vertical for the two surround orientations. We vary the contrast of these gratings, the size of the spatial gap between them, and their relative timing. At equal contrast with no spatial gap, the largest effect typically occurs when centre and surround are presented simultaneously. Varying stimulus contrast affects the asynchrony at which the maximum TI occurs, so that in general presenting the surround earlier produces the largest effect. Introducing a spatial gap between centre and surround tends to reduce the TI magnitude without a clear modulation in temporal properties. These results demonstrate that manipulating the spatial properties of the stimulus can change not only the size of the TI but also its temporal tuning. We argue that manipulations of this kind may prove valuable in disambiguating the role of lateral interactions and intra-cortical feedback in contextual modulation.
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