Neuronal responses to photographs in the superior temporal sulcus of the rhesus monkey.

The activity of a total of 174 visual neurons in the superior temporal sulcus (mostly area TE) of rhesus monkeys was examined quantitatively using complex visual stimuli. Colored photographs of human faces (n = 411), monkeys (n = 308), and non-face objects (n = 35), as well as computer-generated graphics were presented as visual stimuli during a performance of a visual discrimination task. All neurons responded to a limited number of photographs. We quantified these stimulus-selective responses, using two kinds of selectivity indices. With the first index (SI1), we attempted to estimate how many stimuli produced a significant response. The mean value of SI1 was 0.63. About 31% of neurons had values of SI1 greater than 0.8. With the second index (SI2), we attempted to estimate how many stimuli could be distinguished from the stimulus that elicited the strongest activity. The mean value of the SI2 was 0.71. About 51% of neurons had values of SI2 greater than 0.8. About 66% of neurons had values of either SI1 or SI2 that were greater than 0.8, a value that corresponds to a selectivity of one out of five stimuli. We designated these neurons as stimulus-selective (SS) neurons. Of these SS neurons, 45% showed the best response to human faces. Similarly, 28.8% showed the best response to a photograph of monkeys. 7.5% to food, 8.8% to non-food and 10% to simple graphics, such as, a colored square or a circle.(ABSTRACT TRUNCATED AT 250 WORDS)