Abstract

Because spatial information is created by luminance variations across an image, it is not always clear whether neurons at different levels in the visual system are processing spatial information, luminance information, or both. The present paper suggests that, in humans, visual neurons at the pretectal level can convey purely spatial information. Our results show unequivocally that the pupil constricts in response to sinewave gratings formed by local luminance decrements. We infer that the pupil responded to spatial pattern, not to luminance, because the luminance decrement itself would have caused the pupil to dilate, not constrict. Additionally, we infer that both transient and sustained constriction components can be elicited by such pattern stimuli. Responses to spatial pattern and to luminance, however, may not be entirely independent of each other. The pupil response to spatial pattern plus luminance increment or decrement is smaller than the sum of the response to the pattern and the response to the luminance.

© 1992 Optical Society of America