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Harold T. Nefs, Julie M. Harris; An Aubert-Fleischl-like illusion in depth. Journal of Vision 2006;6(6):629. doi: 10.1167/6.6.629.
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© ARVO (1962-2015); The Authors (2016-present)
The Aubert-Fleischl illusion is the false impression that objects move slower when they are pursued with the eyes as compared to when the eyes are kept stationary. Previous research on this illusion has focused on lateral motion and smooth pursuit eye movements. Here, we investigated the relationship between vergence eye movements and the perception of targets moving in depth. Observers saw two intervals sequentially. In each interval there were two targets that were separated vertically by 3 degrees. The top target was a stationary fixation target and the lower target oscillated in depth at eye height. In one of the intervals observers fixated the stationary target and in the other interval they pursued the oscillating target with their eyes. They were asked in which of the two intervals the lower target moved faster. We measured psychometric functions with the method of constant stimuli for speed discrimination. In Experiment 1 we varied the amplitude of the oscillating target; in Experiment 2 we varied the frequency and we kept the amplitude the same. Eye movements were recorded throughout for both eyes. All three observers in Experiment 1 and two out of three observers in Experiment 2 showed systematic biases in the predicted direction. As for the classic Aubert-Fleischl illusion, we demonstrated that a moving target is also likely to be perceived as slower when the eyes follow the target with vergence movements compared to when the eyes remain stationary.
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