Perception
Why does a flickering light seem to last longer?
Open access · cc by · source: Europe PMC
A flickering disk seemed to last longer than a steady one of the same duration, and people also became worse at judging its duration, consistent with the visual system using longer time windows to analyse flicker.
Study at a glance
- Design
- Human experiment — Within-subject two-interval duration discrimination: a flickering (luminance-modulated) standard disk compared with a steady comparison disk; adaptive staircase in Experiment 1, constant stimuli with confidence ratings and ROC analysis in Experiment 2
- N
- Experiment 1: 9 observers; Experiment 2: 6 observers; many trials per observer
- Population
- Young adult observers (mean age 22) at a Japanese research institute
- Outcome
- Time dilation (shift in point of subjective equality), response bias, and sensitivity to duration (d_a)
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Key findings
Flickering disks were judged longer than they were (time dilation), more so for 7 Hz than 3 Hz flicker, for longer standards, and when the flickering disk came second. In Experiment 2 the dilation averaged about 146 ms for the 500 ms standard and about 249 ms for the 1100 ms standard. Flicker also biased responses toward 'longer' and reduced sensitivity to duration, and the second stimulus was judged less precisely than the first; these two losses of sensitivity added together independently. The simulation reproduced these patterns.
Methodology
Observers saw two grey disks one after the other and judged which lasted longer. One disk (the standard, lasting 500 to 1100 ms) flickered in brightness at 3 or 7 cycles per second, while the other was steady and varied in duration. Experiment 1 (9 observers) used an adaptive procedure to find the point at which the two seemed equal; Experiment 2 (6 observers) used fixed durations and confidence ratings so that sensitivity could be separated from response bias. The authors then built a simple simulation in which flicker lengthens the time window used to detect the stimulus's offset.
Limitations
Samples were very small (nine and six observers) with heavy testing of each person, so the results describe a robust within-person effect but say little about individual differences. The integration-window model was only simulated and fitted qualitatively; the study did not measure neural integration windows or rule out attentional explanations directly. Only simple disks with two flicker rates were tested, so it is unclear how far the account extends to complex real-world events.
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