It has been shown that sensory-specific or common processes mediate perception and memory. Here we investigated whether the summation operation of temporal duration is specific to sensory modalities. Two filled intervals were presented as intra- or inter-modal sequence (audition-audition; vision-vision; audition-vision; vision- audition). Participants reproduced the sum (0.6 – 1.1 s) of two intervals. We found that the summation operation of two intervals generally led to an overestimation of the sum, irrespective of conditions. The variations of reproduction were comparable between inter- and intra-modal conditions, indicating no impairment in inter-modal summation of duration. Furthermore, the variations showed positive within-participant correlation between all modality conditions (rs > 0.74). These results suggested that a supra-modal process might mediate the summation of duration. In the subsequent experiment, the similar pattern of results was observed by using short intervals (to be summed to 0.3 – 0.5 s); however, the intra-modal conditions showed much reduced correlations with other conditions (r = 0.39), which indicated that the summation of short durations might be mediated by sensory-specific processes. In sum, the present results suggest two processes for summation of temporal durations: the sensory-specific process that operates only on short durations, and the other supra-modal process that handles otherwise (i.e., when longer durations are to be summed or when inter-modal summation is required).

Time perception; duration; reproduction