Pupil dilation reflects perceptual selection and predicts subsequent stability in perceptual rivalry

Wolfgang Einhäuser, James Stout, Christof Koch, Olivia Carter
PNAS | February 5, 2008 | vol. 105 | no. 5 | 1704-1709

During sustained viewing of an ambiguous stimulus, an individual's perceptual experience will generally switch between the different possible alternatives rather than stay fixed on one interpretation (perceptual rivalry). Here, we measured pupil diameter while subjects viewed different ambiguous visual and auditory stimuli. For all stimuli tested, pupil diameter increased just before the reported perceptual switch and the relative amount of dilation before this switch was a significant predictor of the subsequent duration of perceptual stability. These results could not be explained by blink or eye-movement effects, the motor response or stimulus driven changes in retinal input. Because pupil dilation reflects levels of norepinephrine (NE) released from the locus coeruleus (LC), we interpret these results as suggestive that the LC–NE complex may play the same role in perceptual selection as in behavioral decision making.

Fulltext: http://www.pnas.org/cgi/reprint/105/5/1704

Stimulus-specific competitive selection in macaque extrastriate visual area V4

Mazyar Fallah, Gene R. Stoner, John H. Reynolds
PNAS | March 6, 2007 | vol. 104 | no. 10 | 4165-4169

Macaque visual area V4 has been implicated in the selective processing of stimuli. Prior studies of selection in area V4 have used spatially separate stimuli, thus confounding selection of retinotopic location with selection of the stimulus at that location. We asked whether V4 neurons can selectively respond to one of two differently colored stimuli even when they are spatially superimposed. We find that delaying one of the two stimuli leads to selective processing of the delayed stimulus by area V4 neurons. This selective processing persists when the stimuli move together across the visual field, thereby successively activating different populations of neurons. We also find that this effect is not a spatially global form of feature-based selection. We conclude that selective processing in area V4 is neither exclusively spatial nor feature-based and may thus be surface- or object-based.

Free Fulltext: http://www.pnas.org/cgi/reprint/104/10/4165