Perceptual content, not physiological signals, determines perceived duration when viewing dynamic, natural scenes
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Description: Time perception is a core aspect of human experience, yet the precise cognitive and neural mechanisms underlying it remain unknown. A prominent account is the pacemaker-accumulator model, in which regular ticks of some physiological or neural pacemaker are accumulated and read out as time. A neural substrate for this putative system has been suggested in dopaminergic mid-brain neurons, based on studies indicating that perceptual decisions about time vary with striatal dopamine level, such as following spontaneous blinks. Alternatively, broad physiological processes such as heartbeat have been proposed as pacemaker, as time perception can be modulated by physiological arousal. However, both accounts have difficulty accounting for the intuitive and repeatedly observed finding that time perception varies depending on the content of perceptual experience. Here, we examine evidence for physiological influences on time perception in a large dataset of human duration estimates for naturalistic videos between 1-64 seconds. The content of the videos varied widely, with some depicting walking around a city or countryside, while others depicted more stationary scenes in an office or café. While participants viewed the videos, we recorded their cardiac and eye activity. Participants’ duration estimates were biased according to scene content - rapidly changing city scenes were estimated as longest, more stationary scenes the shortest. Contrary to previous claims, heart rate, pupil size, and blinking were not related to duration estimates. We interpret these results in terms of a recent proposal that tracking change in perceptual classification networks provides a suitable basis for human time perception, indicating that previous assertions of the importance of physiological factors in human time perception should be tempered.