Receptive Field Modulation by Stimulus Density in the Distant Surround
John S. Nafziger1, Shih-Cheng Yen2, and Leif H. Finkel1,2
1Institute of Neurological Sciences
2Department of Bioengineering
3320 Smith Walk, 301 Hayden Hall
University of Pennsylvania
Philadelphia, PA 19104, U. S. A.
Abstract
Psychophysical data on contour detection
(Kovacs et al., 1996; Nafziger et al., 1998) indicate that the distance
over which stimuli influence each other scales inversely with stimulus
density. Related studies (Cannon and Fullencamp, 1991; Polat and Sagi,
1993) have shown that the distant surround is largely suppressive, with
focused regions of facilitation. We propose that stimulus density modulates
the effective size of the distant surround (beyond the classical receptive
field, CRF). High stimulus densities narrow the range of the connection
field, low densities enlarge the effective surround. We present results
of simulations in which the sum of suppressive inputs from the surround
modulate the fall-off with distance of facilitatory connections. These
facilitatory connections then modulate the gain of the CRF. Alternatively,
suppressive inputs from the surround may directly modulate CRF gain. Simulation
results show that such dynamic receptive field mechanisms can account for
the dependence of contour detection on stimulus density.