Contrast sensitivity of neurons in pigeon optic tectum

An analysis of contrast sensitivity of neurons in the optic tectum of intact and wulst-ablated pigeons was carried out using moving light bars. (1) Changes of contrast from 0.1% to 89%, obtained with different bar luminances, induced increases of response amplitude linearly related to log contrast. (2) The units differed in their contrast threshold but 90.7% had a contrast threshold below 2.5%. (3) Both contrast threshold and threshold-saturation range values were independent of the location of the units in the tectal layers. (4) Contrast threshold remarkably increased on passing from low photopic to scotopic adaptation levels. (5) The relationship between unit responses and contrast values, as well as the contrast threshold value, did not differ between intact and wulst-ablated animals.