Equisection of short empty time intervals marked by successive stimuli of different lengths

Several studies have explored how the duration of stimuli delimiting time intervals influences interval judgments and perceived duration. Most focus on nonneighboring intervals and rely on two-alternative forced choice methods, while the method of adjustment and multimodal conditions are rarely used. This study investigated the ability to discriminate two neighboring intervals using an equisection and adjustment method, with variations in the duration of the stimuli marking the intervals, under multimodal conditions. In two experiments, participants adjusted the second of three brief successive signals (10 or 100 ms) marking two empty intervals until they were perceived as equal. In Experiment 1, only the second signal was lengthened to 100 ms. In Experiment 2, the first, third, or both the first and third signals were lengthened. Results from Experiment 1 show that interval judgments are more variable only when the second marker is lengthened within the same modality. Moreover, in intermodal conditions, the interval following the lengthened marker is perceived as longer than the preceding one. Experiment 2 reveals no overall difference in variability across marker-lengthening conditions but consistently shows that the interval following a lengthened marker is perceived as longer, regardless of modality. These findings clarify how stimulus duration and modality influence equisection judgments of short time intervals, shedding light on when and how timing mechanisms operate.