Illusory motion reversals in multiple modalities
Poster Presentation

Alex Holcombe
School of Psychology, University of Sydney

Tatjana Seizova-Cajic
School of Psychology, University of Sydney

     Abstract ID Number: 34
     Full text: Not available
     Last modified: March 5, 2007
     Presentation date: 07/05/2007 10:00 AM in Quad Maclauren Hall
     (View Schedule)

Abstract
A fundamental issue for perceptual processing is whether the system temporally samples the stimulus in discrete fashion, or instead in a non-periodic, more continuous way. The conventional view of continuous, non-periodic analysis has been called into question by a striking illusion in which unambiguously moving stimuli are occasionally perceived to move in the wrong direction. Some have attributed these illusory motion reversals to periodic sampling by the visual system, just as the classical wagon-wheel illusion can be caused by the discrete sampling of a video camera. Here we compare the visual illusion to a proprioceptive phenomenon wherein continuous, unambiguous vibration of the biceps induces illusory forearm extension. Occassionally, reversals occur - the arm is felt to flex rather than extend. Our data comparing the incidence and dynamics of reversals in proprioception and vision suggest that similar mechanisms underlie both. Unlike reversals in vision, proprioceptive reversals cannot be explained by discrete temporal sampling, because the proprioceptive signals provide no opportunity for temporal aliasing. The visual illusion might be caused by a similar mechanism, without periodic temporal sampling.