Arash Yazdanbakhsh¹, Celi Gagliardi²
¹Boston University, ²Boston University
A bistable visual stimulus, such as the Necker Cube or Rubin’s Vase, can be perceived in two different ways which compete against each other and alternate spontaneously. Percept switch rates have been recorded in past psychophysical experiments, but few experiments have measured percept switches while tracking eye movements in human participants. We used the Eyelink II system to track eye gaze position during spontaneous percept switches of a bistable, structure-from-motion (SFM) cylinder that could be perceived as rotating clockwise or counterclockwise. Participants reported the perceived direction of rotation of the SFM cylinder by key presses. Reliability of participant’s reports was ensured by including unambiguous rotations that were generated by assigning depth using binocular disparity. Gaze positions were analyzed up to 2000ms before and after key presses. Our results showed that eye gaze positions 1000 ms before and 1500 ms after percept reports clustered in separate neighborhoods depending on the percept reported, but no such clustering was found beyond that time frame. Direction of eye movement before percept report also depended on which percept was being reported. These findings suggest that percept switches of ambiguous stimuli can be correlated with prior eye gaze positions and velocities, and the visual hemifield where the ambiguous stimulus is located. Future directions include defining a spatial and temporal clustering metric to quantitatively measure the correlation between percept and eye position before, during, and after switches and investigating whether one precedes the other or if there is a bidirectional relationship.
Keywords: Bistable Visual Stimulus, Eye Position