Eye gaze position before, during and after percept switching of bistable visual stimului

Abstract

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. In our study, we use the Eyelink II system to track eye gaze position during spontaneous percept switches of a bistable, structure-from-motion (SFM) cylinder that can be perceived to be rotating clockwise (CW) or counterclockwise (CCW). Participants reported the perceived direction of rotation of the SFM cylinder using key presses. Reliability of participants’ reports was ensured by including unambiguous rotations. Unambiguous rotation was generated by assigning depth using binocular disparity. Gaze positions were measured 50 – 2000 ms before and after key presses. Our pilot data show that during ambiguous cylinder presentation, gaze positions for CW reports clustered to the left half of the cylinder and gaze positions for CCW reports clustered to the right half of the cylinder between 1000ms before and 1500ms after key presses, but no such correlation was found beyond that timeframe. These results suggest that percept switches can be correlated with prior gaze positions for ambiguous stimuli. Our results further suggest that the mechanism underlying percept initiation may be influenced by the visual hemifield where the ambiguous stimulus is located.