Abstract
In the so-called Aubert-Fleischl phenomenon, the speed of an object is underestimated when the observer follows it with their gaze [1, 2]. This is one of the reasons why many experiments on the perception of speed require their observers to keep their gaze on a fixation cross rather than allowing them more naturalistic free viewing. However, when motion is presented embedded in a visual scene the relative motion between background and object might counteract any Aubert-Fleischl-like effects. This study therefore investigates whether pursuing a target with one’s gaze leads to an underestimation of its speed even when its motion occurs in a visual scene. To this end, we immersed participants (n = 8) in a 3D virtual scene where they judged the speed of a single target against the speed of a target cloud in a two-alternative forced-choice task. While the single target was on screen, participants were asked to either keep their gaze on a fixation cross or follow the target. Further, the motion intervals were presented either in a fully black environment that provided no relative motion cues or in a virtual office environment were the objects moved against a textured wall. We found no significant differences in PSEs between the pursuit and fixation conditions in either of the environments. Aubert-Fleischl effects therefore appear not to be strong confounds in experiments relating to the perception of speed, that is, it may not be necessary to restrict participants’ viewing behavior. [1] Aubert, H. (1887). Die Bewegungsempfindung. Pflüger, Archiv Für Die Gesammte Physiologie Des Menschen Und Der Thiere, 40(1), 459–480. https://doi.org/10.1007/BF01612710 [2] Wertheim, A. H., & Van Gelder, P. (1990). An acceleration illusion caused by underestimation of stimulus velocity during pursuit eye movements: Aubert-Fleischl revisited. Perception, 19(4), 471–482. https://doi.org/10.1068/p190471