Research Article Suppression During Binocular Rivalry Broadens Orientation Tuning

ABSTRACT—During binocular-rivalry suppression, an or-dinarily visible stimulus is erased from awareness, but how is the sensory representation of that stimulus affected? Although it is established that rivalry suppression attenu-ates signal strength, the influence of suppression on signal fidelity remains unknown. Here, we show that noise plays a hitherto undiscovered role in the degradation of the percept under suppression. In Experiment 1, we measured psychometric functions for a stimulus presented under dominance and suppression, and found that the slope of these functions was shallower under suppression—a result suggesting that the signal representation was rendered noisier. Experiment 2 then revealed the source of this noise: An examination of the influence of suppression on the orientation bandwidth of noise masking showed that tun-ing bandwidth is significantly broadened under suppres-sion. Thus, the discriminability of a suppressed stimulus is weakened not only by a general decrease in signal strength, but also by broader orientation tuning that in-troduces more noise in the neural representation of the suppressed stimulus. When incompatible stimuli are presented separately to an ob-server’s two eyes, the observer experiences oscillations in per-ception—a compelling phenomenon known as binocular rivalry (Wheatstone, 1838). During binocular rivalry, the stimulus presented to one eye may enjoy periods of dominance lasting several seconds; at the same time, the stimulus viewed by the other eye vanishes from visual awareness. This remarkable phenomenon has piqued the curiosity of psychophysicists and neuroscientists for well over a century (Alais & Blake, 2005), and more recently some researchers have come to believe that rivalry may serve as a tool for studying the neural bases of visua