Speaker
Description
Perception of stimulus duration depends on sensory input statistics. Longer vibrotactile stimuli are perceived as more intense by rats and humans (Fassihi et al., 2017), and stronger stimuli are perceived as lasting longer (Toso et al., 2021). To explain these bidirectional biases, we have proposed leaky integrators for intensity and duration: input from the sensory cortex is accumulated over time downstream, while decaying at a leak rate. The estimated integration time constants (the inverse of the leak rates) are ~70 ms for intensity and ~700 ms for duration. Integration timescales increase along the cortical hierarchy (Murray et al., 2014), suggesting that frontal regions may support temporal accumulation. For vibrations, application of sharp stimulus onset and offset (“flanks”) abolishes the dependence of time perception on input statistics (Ravera, 2026). These complex, paradoxical findings raise questions. What initiates accumulation? What terminates it? Where and how is accumulation implemented in neural circuits? We designed a duration categorization task in which rats classify vibrotactile stimuli as “short” or “long” relative to a fixed boundary. Each trial comprises a pre-stimulus interval (PRE), a vibrotactile stimulus epoch, and a post-stimulus interval (POST), terminated by a go cue. Replicating previous findings, higher-intensity stimuli were judged as longer. Critically, variation in both PRE and POST biased duration judgments: longer and shorter intervals favored “long” and “short” responses, respectively. The effect of PRE was stronger, indicating greater weighting of early evidence. These findings suggest that temporal accumulation is not restricted to the stimulus epoch itself. We therefore consider two hypotheses: (1) rats estimate total elapsed time from nose-poke onset to the go cue, with sensory input simply accelerating an accumulation process; or (2) rats estimate only the task-defined stimulus duration, but this estimate is biased by the adjacent intervals. Recordings of frontal cortical population activity may distinguish between these.
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