Abstract
Background: Potential effects of color to temporal perception has not been sufficiently investigated, when the effect of color red and blue are still controversial. The perceived duration of time is reported to be overestimated induced by hue-arousing color red (e.g., Shibasaki and Masataka, 2014), however, few studies suggest blue was perceived longer (Thönes et al., 2018). Also, study involving monkeys has reported a close relation between perception of passing time and pupil diameter (Suzuki et al., 2016). To this end, this study aims to investigate how our perception of time is associated with pupillary response, which is closely linked to internal factors and neuronal activity in the locus coeruleus. Method: Experimental procedure was based on the latest temporal perception study (Thönes et al., 2018), combining with pupillometry to investigate the correlation between subjective time perception and the pupillary response. In a two-interval duration-discrimination task, two subjectively equiluminant color stimuli (red/blue) were presented continuously on the screen. On each trial, participant indicated which stimulus (former/latter) had been presented for a longer duration, using a numpad. Pupil diameter was recorded by EyeLink 1000PLUS while presentation of the two stimuli. Results and Discussions: The behavioral data suggests that the color red was significantly perceived longer compared to blue stimuli indicated by a shift of the PSE, even though the previous study reported the opposite result. Moreover, sampling trial with the same color condition and same duration condition (which means the two continuous stimuli is physically identical), constriction of the pupillary light reflex (PLR) was significantly larger for stimuli that were judged longer in blue condition, and also slightly larger with red stimuli. These results suggest that subjective temporal perception and pupillary response are somehow directly or indirectly connected, additionally, might be one factor to explain the inconsistent effects of color on time perception.