Anterior inferotemporal neurons of monkeys engaged in object recognition can be highly sensitive to object retinal position

TitleAnterior inferotemporal neurons of monkeys engaged in object recognition can be highly sensitive to object retinal position
Publication TypeJournal Article
Year of Publication2003
AuthorsDiCarlo JJ, Maunsell JHR
JournalJournal of Neurophysiology
KeywordsAction Potentials, Animals, Depth Perception, Electrophysiology, Eye Movements, Form Perception, Macaca mulatta, Male, Neurons, Pattern Recognition, Photic Stimulation, Psychomotor Performance, Retina, Temporal Lobe, Time Factors, Visual, Visual Fields, Visual Perception

Visual object recognition is computationally difficult because changes in an object's position, distance, pose, or setting may cause it to produce a different retinal image on each encounter. To robustly recognize objects, the primate brain must have mechanisms to compensate for these variations. Although these mechanisms are poorly understood, it is thought that they elaborate neuronal representations in the inferotemporal cortex that are sensitive to object form but substantially invariant to other image variations. This study examines this hypothesis for image variation resulting from changes in object position. We studied the effect of small differences (+/-1.5 degrees ) in the retinal position of small (0.6 degrees wide) visual forms on both the behavior of monkeys trained to identify those forms and the responses of 146 anterior {IT} {(AIT)} neurons collected during that behavior. Behavioral accuracy and speed were largely unaffected by these small changes in position. Consistent with previous studies, many {AIT} responses were highly selective for the forms. However, {AIT} responses showed far greater sensitivity to retinal position than predicted from their reported receptive field {(RF)} sizes. The median {AIT} neuron showed a approximately 60% response decrease between positions within +/-1.5 degrees of the center of gaze, and 52% of neurons were unresponsive to one or more of these positions. Consistent with previous studies, each neuron's rank order of target preferences was largely unaffected across position changes. Although we have not yet determined the conditions necessary to observe this marked position sensitivity in {AIT} responses, we rule out effects of spatial-frequency content, eye movements, and failures to include the {RF} center. To reconcile this observation with previous studies, we hypothesize that either {AIT} position sensitivity strongly depends on object size or that position sensitivity is sharpened by extensive visual experience at fixed retinal positions or by the presence of flanking distractors.

Refereed DesignationRefereed

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