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http://www.nature.com/natureneuroscience
Web End = Reduction of stimulus visibility compresses apparent time intervals
http://www.nature.com/natureneuroscience
Nature Publishing Group
Masahiko Terao1,2, Junji Watanabe1,3, Akihiro Yagi2 & Shinya Nishida1
The neural mechanisms underlying visual estimation of subsecond durations remain unknown, but perisaccadic underestimation of interash intervals may provide a clue as to the nature of these mechanisms. Here we found that simply reducing the ash visibility, particularly the visibility of transient signals, induced similar time underestimation by human observers. Our results suggest that weak transient responses fail to trigger the proper detection of temporal asynchrony, leading to increased perception of simultaneity and apparent time compression.
Accurate estimation of subsecond durations ranging from tens to hundreds of milliseconds is a critical visual sensory ability for dynamic event recognition and visuomotor coordination. A recent study1 provided an important clue as to the neural mechanism governing the encoding of time intervals of this range. Observers in that study consistently underestimated a 100-ms interval between two ashes by about 50 ms when the pair of ashes was immediately followed by a saccade. Studies13 have suggested a possible link between this interval underestimation and the nding that saccades induce momentary changes in spatiotemporal tunings of neurons in high-level visual areas, such as the middle temporal area4 and the lateral intraparietal area5. This hypothesis, however, still awaits further empirical validation. An alternative, although not exclusive, possibility tested in this study is that the interval underestimation might be related to saccadic suppression of visual response, which, arguably, is selective for transient responses mediated by magnocellular mechanisms6. Consistent with this hypothesis, we found that the reduction of stimulus visibility without saccades could cause apparent underestimation of interash intervals.
In each trial of our experiment, observers made a judgment as to the relative length of two sequentially presented temporal intervals, each dened by a pair of red ashes appearing at the top and bottom of an equiluminant green eld (Supplementary Methods online). The rst interval (test interval) was xed at 100 ms, whereas the second one (probe interval) was varied. Using a constant stimuli method, we estimated the apparent test interval from the point of subjective equality (the 50% point of the cumulative Gaussian function tted
to the psychometric function). The test interval was judged...