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Abstract

We trained monkeys to identify objects in the presence of varying amounts of visual noise in a delayed-matching-to-sample paradigm. Monkeys were presented with a brief cue object, which could be either a novel or familiar object at one of several stimulus levels ranging from 0 (visual noise) to 100 (undegraded object). After a brief delay, an undegraded probe object was presented and monkeys had to release a lever if the sample matched this test object. We used colored images of natural scenes, faces, etc. presented at the center of gaze. Experience with a particular set of objects allowed monkeys to identify them in the presence of greater amounts of noise compared to novel objects. We have previously shown that object-selective neurons in macaque prefrontal cortex reflect this behavioral improvement (RainerMiller, Neuron 27:179-189, 2000). By recording the activity of single neurons from eight electrodes simultaneously placed in parafoveal extrastriate area V4, we aim to describe the role of these neurons in communicating information about degraded objects, and examine if and how this information is modified by visual learning. We have preliminary data from 83 neurons from one monkey. Many neurons reliably communicated information about both novel and familiar degraded objects. At intermediate stimulus levels, these neurons signalled more information about familiar than about novel objects, consistent with a possible involvement in the behavioral improvements. In addition, we observed a tendency for undegraded familiar objects to elicit more activity than novel objects early on in the visual response. These findings suggest that visual experience can modify the properties of neurons in extrastriate area V4, and that learning already begins to affect neurons relatively early in the visual processing hierarchy.