Cortical Surround Interactions and Perceptual Salience via Natural Scene Statistics
Figure 5
Co-assignment probability depends on image contrast.
(A) Probability for the vertical center and surround RFs as a function of grating contrast. The stimulus diameter is 7 pixels. All the RFs have diameter 9 pixels, and the mid point of each surround RF is located 6 pixels away from the mid point of the center RF, so a stimulus 7 pixels wide encroaches on the surround RFs. Although it does so only by 2 pixels, in the simulations this leads to a large co-assignment probability at high contrast; we have verified that this is not the case for a stimulus 5 pixel wide (in which case the overlap with surround RFs is even smaller, and not enough to recruit the surround). (B) Probability for the vertical center and surround RFs on natural images. The X axis represents values of for vertical RFs (k, S), with covariance matrix
. The term
therefore increases for larger values of the RF outputs (note that for any fixed image, scaling the contrast by a factor c also scales
by c). For each input image, we computed
and the co-assignment probability for the configuration
; the Y axis represents the mean of such probability across the inputs corresponding to given values of
. The dashed line corresponds to the prior probability learned by the model on natural images.