Georgeson M A, 2000, "Different contrast response functions underlying contrast adaptation and the tilt aftereffect" Perception 29 ECVP Abstract Supplement
Different contrast response functions underlying contrast adaptation and the tilt aftereffect
M A Georgeson
What can we learn from aftereffects about the selectivity, contrast response, and adaptive properties of visual coding mechanisms?
I modelled the tilt aftereffect (TAE) by assuming that the response of each orientation-selective neuron is represented by a contrast-gain-control equation in which the divisive term contains a pattern-selective effect of adapting contrast and a nonselective effect of test contrast. Encoded orientation was the vector sum of responses across cells. The TAE was measured by a nulling method for gratings of 2 cycles deg-1, with adapting and test contrasts from 4% to 64%. The TAE peaked around ±20° adapting orientation and grew almost linearly with log adapt : test contrast ratio. Data were well fit (r = 0.97) by the model with Gaussian orientation tuning of each unit (σ = 7.2°) but only when the response was compressive over the whole contrast range. This is very different from the accelerating response at low contrasts that is required to model contrast discrimination and the loss of perceived contrast after adaptation, and is shown by V1 cells. Thus the TAE may reflect a later, more contrast-invariant stage whose role is orientation coding, not contrast coding. The finding of substantial TAE transfer between first-order and second-order gratings further supports this view.
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