Coding of image contrast in central visual pathways of the macaque monkey.

Measurements of contrast sensitivity were obtained from isolated neurons in the lateral geniculate nucleus, striate cortex, and middle temporal visual area of macaque monkeys. Between the lateral geniculate nucleus and the middle temporal area contrast sensitivity functions become progressively steeper. Furthermore, many neurons in the middle temporal area are more sensitive than any cell encountered in early stages. Measurements made with stimuli of different sizes show that this high sensitivity depends on areal summation across the receptive field.