Abstract
Background: When observers view ambiguous figures for prolonged period of time, they experience perceptual alternations between two possible visual interpretations (Leopold & Logothetis, 2003). Dubbed bistable perception, this phenomenon has been considered as a useful means to study visual awareness since it induces spontaneous fluctuation in awareness despite constant physical stimulation (Kim & Blake, 2005). To investigate whether visual awareness during bistable perception is affected by emotional valence associated with one of two interpretations, we exploited Pavlovian fear conditioning (Pavlov, 1927). Methods: Among a variety of ambiguous figures, we selected man-rat and duck-rabbit which induced balanced perceptual alternations in a pilot test. Prior to and following conditioning, observers tracked their perceptual experiences during 12 100-sec trials (6 for each ambiguous figure) by depressing one of two keyboard buttons. During conditioning, a pair of unambiguous variants of the man-rat figure was used as conditioned stimuli (CS). For a half of the observers tested, the man image (CS+) was paired partially with electrical finger shock (US) while the rat image (CS-) was unpaired with the electrical shock. For the other half, the rat image was CS+ while the man image was CS-. Reaction time was measured following observers' 2-AFC discrimination task (man or rat) to assess conditioning effect independently. Anxiety test was also given to all observers. Results: For observers who showed faster response to CS+ paired with the shock than to CS- during conditioning, perceptual awareness of CS+ during bistable perception increased following conditioning. Besides, observers who marked high anxiety scores tend to perceive CS- longer following conditioning. Conclusion: Perceptual awareness during bistable perception is affected by fear conditioning. Individual differences in susceptibility of conditioning and the level of anxiety are influential factors.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0089090).