Detection uncertainty and the facilitation of chromatic detection by luminance contours

A suprathreshold luminance flash (1°, 200 msec) on a large uniform yellow field facilitates detection of a coincident (1°, 200 msec) red or green equiluminant flash and approximately linearizes the psychometric function for detecting the chromatic flash. The facilitation is produced by the suprathreshold contour created by the luminance flash. We tested whether the contour facilitates detection by reducing spatiotemporal uncertainty in detecting the chromatic flash. Uncertainty increases false alarms, and this effect can be factored out by correcting yes–no psychometric functions for guessing. Uncertainty also alters the shape of the receiver operating characteristic. Measurements of yes–no psychometric functions and receiver operating characteristics do not support the uncertainty reduction hypothesis.