Evidence accumulation explains the duration of perceptual experience and its associated confidence

Evidence accumulation is a fundamental process whereby noisy sensory information is accumulated over time up to a threshold. Although numerous studies have explored the link between evidence accumulation and decision formation, its contribution to perceptual consciousness remains unclear. Here, we propose a leaky evidence accumulation model that accounts for qualitative aspects of perceptual experience such as its perceived onset and duration, as well as confidence in perceptual judgments. Our model assumes that the onset of perceptual experience (i.e., stimulus detection) is triggered by the crossing of a perceptual bound by the accumulation process. Crucially, we hypothesized that perceptual experience lasts as long as accumulated evidence remains above the threshold, and that confidence is read out from the maximum reached by accumulated evidence over time. We tested these predictions in a pre-registered computational modelling study. Four healthy participants were asked to detect 3500 faces with different intensities and durations and either report their confidence in having perceived a face or no face or reproduce the duration of their perceptual experience of a face. As predicted, participants detected better and faster stimuli with high intensity or longer physical durations. Similarly, faces presented at high intensity or long duration were perceived with longer subjective durations and higher confidence. We fitted our computational model to response times and detection performance using the Variational Bayesian Monte Carlo toolbox. Using this model, we could parsimoniously reproduce effects of stimulus intensity and duration on perceived duration and confidence better than with alternative models that were not based on leaky evidence accumulation. Together, these results support leaky evidence accumulation as a mechanism explaining stimulus detection, but also some phenomenal aspects of perceptual experience such as subjective duration and confidence.