Abstract
Everybody knows roughly how long one second lasts. How does such an internal duration template affect perceived time? We investigated an illusion where the first visual item in a repeating sequence appears to last longer ("debut chronostasis"). Earlier studies explained this either by increased attention towards the first item or relatively suppressed neural encoding for the repeated ones. However, previous studies overlooked two confounding factors by keeping the first item the target with variable duration across trials. First, the target defined by instruction may create a cognitive bias (instruction effect). Second, the variable item across trials may implicitly draw more attention or activate memory encoding processes, so as to modulate perceived time (uncertainty effect). In a duration discrimination task (Experiment 1), the three target-reference pairs were defined by instruction as 1st-2nd, 2nd-1st, and 2nd-3rd in separate blocks. As expected, 1st-2nd produced chronostasis and 2nd-3rd did not. In the novel 2nd-1st condition, debut chronostasis was largely reduced. This excluded the attention and the repetition suppression hypotheses because both predict the same illusion in the 1st-2nd and 2nd-1st conditions, leaving the instruction or the uncertainty effects as plausible explanations. In Experiment 2, the explicit instruction was the same regarding which item was the target, but the variable item was the reference instead. The results supported the uncertainty, but not the instruction effect. In both experiments, the relative duration between the 2nd and the 3rd items did not significantly differ; only when the first item had uncertain duration across trials, debut chronostasis occurred. Therefore, an internal duration template based on recent stimuli history may be calibrated at the first item per trial and disrupted when the first time varies in duration. Future studies shall take this newly-identified effect into account, and investigate how the first-item uncertainty leads to time expansion rather than compression.
Meeting abstract presented at VSS 2018