Abstract
I will present results from a series of experiments investigating how simple scenes with crowding and partial occlusion are encoded in midlevel stages of the ventral visual pathway in the macaque monkey. Past studies have demonstrated that neurons in area V4 encode the shape of isolated visual stimuli. When these stimuli are surrounded by distractors that crowd and occlude, shape selectivity of V4 neurons degrades, consistent with the decline in the animal’s ability to discriminate target object shapes. To rigorously test whether this is due to the encoding of “pooled” summary statistics of the image within the RF, we characterized responses and selectivity for a variety of target-distractor relationships. We find that the pooling model is a reasonable approximation for neuronal responses when targets and distractors are either all similar or all different. But when the distractors are all similar and can be perceptually grouped, the target becomes salient by contrast. This saliency is reflected in the neuronal responses and animal behavior being more resistant to crowding and occlusion. Thus, target saliency in terms of featural contrasts trumps pooled encoding. These results are consistent with a normalization model where target saliency titrates the relative influence of different stimuli in the normalization pool.