TEMPORAL ANALYSIS OF THE CRAIK-O’BRIEN-CORNSWEET EFFECT

M. P. Davey, T. Maddess and M. V. Srinivasan

Purpose:

Models of the Craik-O’Brien-Comsweet Effect (COCE) differ in their predictions as to whether the COCE should require time to form or whether the percept is formed instantaneously. In particular theories presented by [Grossberg S. and Todorovic (1988) Pecept. Psycho. 43, 241-277] would require some time for the induced brightness percept to fill the gap between the defining luminance edges.

Methods: Experiments on 7 subjects employing grating versions of the COCE examined the critical contrast reversal rate at which brightness modulation of the central regions of the COCE stripes in the gratings disappeared. Other experiments examined the visibility of the waveforms related to the fundamentals of squarewave gratings having comparable spatial frequencies.

Results: A finite time was required for the brightness induction. Consideration of human cortical magnification in various visual areas revealed that cortical propagation rates like those in epilepsy would explain the data if either Vi or V2 were the relevant visual area. Visibility of the fundamental of comparable square waves could not explain the COCE.

Conclusions: A spreading mechanism appears to be required for the production of the COCE.