NEURAL CODING OF VISUAL STIMULI

点击翻译按钮获取中文摘要

To study the mechanisms underlying visual perception we recorded the activity of ganglion cell fibers, the fibers that send visual information from the retina to the brain, and compared it with the activity of single neurons in the lateral geniculate nucleus and primary visual cortex, the first two extraretinal stages of visual processing, and inferior temporal cortex, the last visual processing station in the cortex. The three sets of neuronal recordings all showed different temporal response patterns to different visual stimulus patterns. When neurons were analyzed as communication channels carrying information about visual stimuli in their responses, the response patterns could on e represented as the sum of several (3-6) simultaneous, independent patterns of activity. These activity patterns were analyzed as a temporal code, and this code was found to contain more information than that conveyed by the response strength, the usual measure of neuronal response. Through application of our information theoretical analysis we have found that the proportion of information carried in the temporal code increases as the information moves farther from the retina within the visual system. Thus, temporal modulation carries a significantly greater proportion of visual information outside of the retina. We have also found that removal of feedback from visual cortex alters stimulus-dependence, and hence the messages, of lateral geniculate neurons Given that the anatomical basis of this feedback is duplicated throughout the visual system, this strongly suggests that feedback is required for formation of normal stimulus-related messages. We have also found that the messages of sequentially presented pictures are independent when the stimuli are separated by as little as 30 msec showing that decoding of temporally modulated stimulus-related messages may be easily carried out.