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Bernard M ‘t Hart, Denise Y.P. Henriques, Patrick Cavanagh; Manual tracking of the double-drift illusion. Journal of Vision 2019;19(10):286b. https://doi.org/10.1167/19.10.286b.
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When a target has poor position information, vision may take the target’s motion into account in generating its perceived location, resulting in conflicts between apparent and actual position. The double-drift illusion (Lisi & Cavanagh, 2015) is one such case in which the internal motion of the target drives an accumulating perceived offset that, after as much as 2 to 4 seconds, reaches some saturation limit where the accumulation stops or resets to the physical location. To investigate this illusion and its limits, we asked participants to move a pen over a drawing tablet to continuously track where they perceived the stimulus. By interposing an angled mirror, the participants were able to see the target moving on the same horizontal surface where they moved the stylus but could not see their hand or the stylus. We found that the manual tracking data showed the double-drift illusion and that its magnitude was sensitive to the internal and external speeds of the moving gabor, being largest when the external speed was slow and the internal speed high. This indicates that the manual tracking data can in principle be used to follow the perceived target location moment by moment to investigate how and when the illusory position shift saturates.
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