THERE IS NO EVIDENCE THAT KANIZSA-TYPE SUBJECTIVE CONTOURS CAN BE DETECTED IN PARALLEL

Davis and Driver presented evidence suggesting that Kanizsa-type subje ctive contours could be detected in a visual search task in a time tha t is independent of the number of nonsubjective contour distracters. A linking connection was made between these psychophysical data and the physiological data of Peterhans and von der Heydt which showed that c ells in primate area V2 respond to subjective contours in the same way that they respond to luminance-defined contours. Here in three experi ments it is shown that there was sufficient information in the display s used by Davis and Driver to support parallel search independently of whether subjective contours were present or not. When confounding pro perties of the stimuli were eliminated search became slow whether or n ot subjective contours were present in the display. One of the slowest search conditions involved stimuli that were virtually identical to t hose used in the physiological studies of Peterhans and von der Heydt to which Davis and Driver wish to link their data. It is concluded tha t while subjective contours may be represented in the responses of ver y early visual mechanisms (eg in V2) access to these representations i s impaired by high-contrast contours used to induce the subjective con tours and nonsubjective figure distracters. This persistent control pr oblem continues to confound attempts to show that Kanizsa-type subject ive contours can be detected in parallel.