The responses of single neurons in the temporal visual cortical areas of the macaque when more than one stimulus is present in the receptive field.

Neurons in the temporal visual cortical areas of primates have large receptive fields, which can show considerable selectivity for what the stimulus is irrespective of exactly where it is in the visual field. This is called translation invariance. However, such results have been found when there is only one stimulus in the visual field. The question arises of how the visual system operates in a cluttered environment. To investigate this we measured the responses of neurons with face-selective responses in the cortex in the anterior part of the superior temporal sulcus of rhesus macaques performing a visual fixation task. We found that the response of neurons to an effective face centred 8.5 degrees from the fovea was decreased to 71% if an ineffective face stimulus for that cell was present at the fovea. In a similar way, introduction of a parafoveal ineffective face stimulus decreased the responses of these neurons to an effective face stimulus at the fovea to 75%. In addition to these interactions, it was found that an effective stimulus object at the fovea produced a larger response than when it was parafoveal, and that this weighting towards an object at the fovea was also seen when more than one object was present in the visual field. The implication of this weighting of the responses of neurons towards objects at the fovea, even in an environment with more than one object present, is that the output of the visual system provides information to subsequent systems particularly about objects at the fovea, so that learning about these objects (and less about other objects elsewhere in the visual field) is facilitated.