Contrast gain control and fine spatial discriminations.

The effect of contrast gain control mechanisms on discrimination between highly similar simple and complex stimuli is examined, with a focus on how discrimination accuracy changes as a function of the contrast of stimulus components. Two models of contrast gain control are evaluated. In both, the response of each pathway is attenuated by a factor determined by the total activity in a large pool of pathways. One model bases attenuation on the sum of linear filter responses within this pool; the other, based on Heeger's contrast energy-driven model [J. Neurophysiol. 70, 1985 (1993)], uses squared filter response. Predictions generated from the models are compared with data from experiments reported here and from the literature. Predictions are made for simple grafting stimuli of different sizes and for stimuli to which a second grafting component is added either as a second cue or as a mask. With one exception, predictions of the models agree closely with each other and with the data. The exception is a masking study that differentiates the models and supports the filter-driven model over the energy-driven model.