Measuring White's illusion during brief stimulus displays

Alan Robinson
Cognitive Science, UCSD

Virginia de Sa
Cognitive Science, UCSD

Abstract
What is the time course of brightness perception and brightness illusions? Previous research has suggested that brightness induction is a slow process and is only visible for temporal frequencies below 4hz. Here, we introduce a new paradigm for measuring the time course of brightness processing which can be applied to more complex figures, such as White’s illusion. In our paradigm the stimulus is shown briefly (On_time= 70, 82, 117, or 1120ms, depending on condition), and then covered by a noise mask (900ms) while the subject adjusts the brightness of a matching patch. The display alternates between noise mask and the stimulus until the subject is satisfied with the match, which typically took 30 to 60 seconds.

Using this technique we found that White’s illusion remains clearly visible in most subjects when On_time was just 82ms. For shorter On_times we found that most subjects could no longer reliably see the stimuli, and therefore could not make brightness matches. These results suggest that either brightness processing (1) is complete 82ms after stimulus presentation, or (2) can continue to proceed even after the stimulus has been removed and replaced with a noise mask.

Funding:
NSF Grant DGE-0333451 to GW Cottrell and NSF CAREER Award 0133996 to VR de Sa