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Masahiko Terao, Junji Watanabe, Akihiro Yagi, Shin'ya Nishida; Flash visibility degradation compresses apparentbrief inter-flash intervals as does saccadic eye movement. Journal of Vision 2007;7(9):385. doi: 10.1167/7.9.385.
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The duration perception of visual events is considered to rely on a variety of mechanisms depending on the time scale. For brief durations, sensory mechanisms are likely to play critical roles. For instance, adaptation to higher or lower temporal frequencies can change the apparent duration of ∼500 ms dynamic stimuli (Johnston et al, 2006, Curr Biol, 16, 472–479). For even shorter durations, Morrone et al. (2005, Nat. Neurosci, 8, 950–954) found that the interval defined by two colored flash bars (∼100ms) was perceptually compressed by about one half when the flashes were presented immediately before a saccade. Here we show the occurrence of a similar illusory compression of perceived time without saccades. Using a display similar to Morrone et al., we presented two red flash stimuli sequentially on an equiluminannt green background, one on the top and the other on the bottom of the display, with an interval of 100 ms. The red flashes were presented under steady fixation, but with dynamic random luminance modulation of the stimulus areas (within ±25%, 120Hz update), which was introduced to mask transient visual responses to the flash stimuli. The apparent duration of these intervals were compared with an interval defined by a subsequent flash pair presented without the luminance noise. The results indicate that the apparent flash interval is reduced when it is presented with luminance noise, in a similar way to flashes presented before a saccade. We also found a similar compression effect in static displays when the flash visibility was degraded by reducing the chromatic contrast of the target flash bars relative to the background. This compression was not observed for a longer interval (500 ms). These findings indicate that visual neural encoding of brief intervals of the order of 100 ms is strongly affected by the visibility of stimuli.
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