Abstract
Bistable figures provide a fascinating window through which to explore human visual awareness. This is because a constant visual stimulus induces a dynamic alternation between two distinct percepts over time. Here we provide evidence that a background auditory soundtrack (that was semantically congruent with one or other percept) can modulate people's perception of bistable figures; we then further test whether this factor interacts with the factors of selective attention and fixation position that have previously been shown to influence the perception of bistable figures (Meng & Tong, 2004). The participants viewed the “my wife or my step-mother” figure and reported their dominant percept continuously. In Experiment 1, the participants reported seeing the old woman (young lady) for more of the time when listening to the voice of an old woman (young lady). In Experiment 2, this auditory modulation of bistable figure perception was observed regardless of where the participants were instructed to focus their fixation. In Experiment 3, attending to a specific view was found to dominate the percept of the bistable figure and this factor overrode the modulation of bistable perception by auditory semantic congruency. These results therefore suggest that in the process by which a conscious percept emerges when viewing a bistable figure, the modulation of both semantic congruency and selective attention were independent of the low-level factors of overt fixation position; however, the influence of selective attention is more powerful than that of auditory semantic congruency. These results also imply that the modulation of top-down factors of selective attention and semantic congruency on the formations of visual awareness in ambiguous situations may be weighted differently, such as when comparing bistable figures and binocular rivalry (see Chen, Yeh, & Spence, submitted).
Acknowledgments: This research was supported by a joint project funded by the British Academy (CQ ROKK0) and the National Science Council in Taiwan (NSC 97-2911-I-002-038).