See Presentation at (9PM ~ 10PM) https://meet.google.com/fao-zkqw-fea
Woochul Choi, Hyeonsu Lee, Se-Bum Paik
When an ambiguous sensory stimulus is given, our brain often actively interprets the given stimulus to dissolve ambiguity. A particular example is the condition of “bistable perception” where a given stimulus can be interpreted as two different states: Under this ambiguity, our perception alternates between two possible interpretations quasi-periodically with switching frequency varying across individuals. This characteristic dynamics of bistable perception is thought to reveal how the brain recognizes incomplete visual signals to lead to a perceptual decision, and a number of studies have been performed to investigate the mechanism of its rhythmic perceptual alternation. However, understanding the dynamics of bistable perception has proved elusive, as it is a complicated process involving interrelated cognitive and motor processes even including top-down intention and eye movements. Recent studies reported that specific eye movement occurs during bistable perception [1], but it is still not known whether eye movements can actively induce perceptual decision, or they are just accompanied after the decision. Here, we show that eye movement may not solely induce perceptual behavior, but the eye movement patterns reflect the perceptual decisions for interpretation of ambiguous stimuli. We performed a human psychophysics experiment with simultaneous eye-tracking, using three bistable stimuli — racetrack, rotating cylinder, and Necker cube. We found that eye gaze slowly oscillates with 5-10s intervals, the period of which was positively correlated to the frequency of perceptual switch. In addition, we found that eye gaze movements were observed in the opposite directions before two different perceptual decisions are made. The preceding eye gaze can thus predict the perceptual decision with ~90% accuracy. We also found that the frequency of the saccadic eye movement during free viewing, which does not require any active interpretation, was correlated with the period of perceptual switch, implying that dynamics of eye movement reflects the characteristic of bistable perception. Next, to isolate the effect of eye movement from intention, we first asked the subjects to have a strong intention to switch (or stay) their perceived state during experiments. With such manipulations, we found that both perceptual decision and eye movements were significantly altered, compared to the case of non-intended trials. We then controlled visual stimuli so that the subject’s eye movement follows the traces of intention-controlled trials, without actual intention to change their behavior. Under this condition, even though subjects’ eye movements mimic those of the intended trial, perceptual decisions were not significantly biased. This suggests that eye movements alone cannot bias perceptual behavior in bistable perception. Taken together, the results suggest that 1) rhythmic eye movement correlates with active visual perception, 2) preceding eye gaze trajectory predicts individual decision but 3) eye movement may not solely induce perceptual decision. These results collectively suggest a relationship between eye movement control, top-down intention, and active perception.
Acknowledgements
This research was supported by National Research Foundation of Korea, Grant Number: 2019M3E5D2A01058328, 2019R1A2C4069863
References
1\. Polgári P et al.,Novel method to measure temporal windows based on eye movements during viewing of the Necker cube. PLoS One.2020(15)
