Leaky evidence accumulation accounts for perceptual confidence and subjective duration
Perceptual consciousness is defined as the subjective experience associated with the processing of sensory cues from the environment. Subjective experience unfolds over time and is accompanied by a sense of confidence, yet the mechanisms underlying these two properties remain elusive. Here, we propose a computational mechanism that accounts not only for the onset of subjective experience but also its subjective duration and associated feeling of confidence. Our model assumes that a percept becomes conscious when an ongoing, leaky accumulation of sensory evidence surpasses a perceptual threshold and stops being conscious when it falls back below the threshold due to leakage. Crucially, this perceptual threshold can be lower than the decision threshold for reporting the percept. Moreover, our model derives confidence in accurately detecting sensory evidence from the maximum reached by the evidence accumulation process following stimulus onset. We conducted a preregistered study in which three distinct models of evidence accumulation were fitted to behavioral reports of detection, confidence, and subjective duration during a face detection task under temporal uncertainty. The leaky evidence accumulation model accounted for the observed behavioral data best and outperformed alternative models without leakage. In a follow-up experiment, we investigated the impact of leakage adaptation on detection and subjective duration. We found that changes in leakage induced by contextual variations of face duration influenced both detection rates and subjective duration, as predicted by our model. Altogether, our findings suggest that leaky evidence accumulation is a suitable candidate mechanism to explain qualitative aspects of subjective experience, including subjective duration and feelings of confidence.