Eye-movement patterns for perceiving bistable figures.

Bistable figures can generate two different percepts alternating with each other. It is suggested that eye fixation plays an important role in bistable figure perception because it helps us selectively focus on certain image features. We tested how the shift of percept is related to the eye-fixation pattern and whether inhibition of return (IOR) plays a role in this process. IOR refers to the phenomenon where, after attention remains at the same image location for a period, the inhibition to the mechanisms supporting that location increases. Consequently, visual attention shifts to a new location, and reallocation to the original location is suppressed. We used an eye tracker to record the observers' eye movements during observation of the duck/rabbit figure and the Necker cube while recording their percept reversals. In Experiment 1, we showed there were indeed different eye fixation patterns for different percepts. Also, the fixation shifted across different regions that occurred before the percept reversal. In Experiment 2, we examined the influence of inward bias on the duck/rabbit figure and found that it had a significant effect on the first percept but that this effect diminished over time. In Experiment 3, a mask was added to the attended region to remove the local saliency. This manipulation increased the number of percept reversals and fixation shifts across different regions. That is, the change in local saliency can cause a fixation shift and thus reverse our perception. Our result shows that what we perceive depends on where we look.