In article <3AB70038.1FD2B50 at cs.unm.edu>, Keith Wiley <kwiley at cs.unm.edu> wrote:
>Contrast sensative cells get a lot of attention. On-center, off-center,
>line, edge, etc. Is there any evidence that there are cells anywhere in
>the visual system that respond positively to a lack of contrast, to
>smooth excitation across the receptive field?
Depends a bit on what you want Keith.
Photoreceptors behave this way.
Higher in the visual system, the "complex" cells of the primary visual cortex
have receptive fields that are not centre-surround type.
In practice, the centre-surround structure is never "textbook perfect" and
most cells in the visual cortex will provide some response to a uniform
brightness stimulus if it is different from the background, it is just that it
is possible to find other stimuli (bars, textures whatever) that evoke a much
stronger response.
Dr Richard Vickery
School of Physiology & Pharmacology, UNSW, Australia, 2052
ph. 61 2 93851676, fax 61 2 93851059
http://www.med.unsw.edu.au/Physiology/School/staff/vickery/Welcome.html
