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要旨:
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.
