THE RESPONSES OF SINGLE NEURONS IN THE TEMPORAL VISUAL CORTICAL AREASOF THE MACAQUE WHEN MORE THAN ONE STIMULUS IS PRESENT IN THE RECEPTIVE-FIELD

Neurons in the temporal visual cortical areas of primates have large r eceptive fields, which can show considerable selectivity for what the stimulus is irrespective of exactly where it is in the visual field, T his is called translation invariance. However, such results have been found when there is only one stimulus in the visual field. The questio n arises of how the visual system operates in a cluttered environment. To investigate this we measured the responses of neurons with face-se lective responses in the cortex in the anterior part of the superior t emporal sulcus of rhesus macaques performing a visual fixation task. W e 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 sti mulus for that cell was present at the fovea. In a similar way, introd uction of a parafoveal ineffective face stimulus decreased the respons es of these neurons to an effective face stimulus at the fovea to 75%. In addition to these interactions, it was found that an effective sti mulus 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 tha t learning about these objects (and less about other objects elsewhere in the visual field) is facilitated.