The Duncker illusion: intersubject variability, brief exposure, and the role of eye movements in its generation.

PURPOSE The Duncker illusion, also known as induced motion, is the illusory component of an object's motion that results from background movement. The origins of this robust phenomenon are still subject to debate. The goal of this study was to examine the role eye movements play in its generation. METHODS The Duncker illusion was generated by rear-projecting an LED target and a random-dot background onto a semitranslucent screen. Each moved under independent control of mirror galvanometers. The background was either stationary or moved vertically, whereas the target moved horizontally with various degrees of a vertical component. Using a two-alternative, forced-choice cancellation paradigm involving multiple interleaved staircases, seven human subjects quantified the illusion under a variety of conditions. These conditions included varying the exposure time from 50 to 200 ms. RESULTS The strength of the illusion did not decrease, even when exposures too brief to generate eye movement were used. Four of the subjects showed no difference between long and short exposures (P > 0.12). In two the illusion was stronger for short exposures (P < 0.05), and in one the illusion was not quantifiable. There was little intrasubject variability across trial types, yet there was a large intersubject variability in the strength of the illusion. CONCLUSIONS The illusion is robust in that it is perceived under a wide variety of conditions by all observers. By varying the parameters, it was possible to demonstrate that eye movements do not play a role in generating the illusion and that this robust illusion is most likely caused by the visual system attributing relative motion between target and background to target motion and ignoring any true background movement. The mechanism by which this occurs varies in degree between individuals.

[1]  Shinsuke Shimojo,et al.  A slowly moving foreground can capture an observer’s self-motion — a report of a new motion illusion: inverted vection , 2000, Vision Research.

[2]  The Aubert-Fleischl paradox does appear in visually induced self-motion , 1991, Vision Research.

[3]  R. John Leigh,et al.  Tracking of illusory target motion: Differences between gaze and head responses , 1995, Vision Research.

[4]  N. Kitajima,et al.  Dynamic Capture of Sound Motion by Light Stimuli Moving in Three-Dimensional Space , 1999, Perceptual and motor skills.

[5]  James A. Crowell,et al.  Estimating heading during eye movements , 1994, Vision Research.

[6]  Leonard Brosgole,et al.  The role of eye movements in the perception of visually induced motion , 1968 .

[7]  Lance M. Optican,et al.  Unix-based multiple-process system, for real-time data acquisition and control , 1982 .

[8]  R B Post.  Induced Motion Considered as a Visually Induced Oculogyral Illusion , 1986, Perception.

[9]  L F Dell'Osso,et al.  Saccades to remembered targets: the effects of smooth pursuit and illusory stimulus motion. , 1996, Journal of neurophysiology.

[10]  R D Easton,et al.  Information processing analysis of the Chevreul pendulum illusion. , 1975, Journal of experimental psychology. Human perception and performance.

[11]  R. D. Easton,et al.  An experimental analysis of the Chevreul pendulum illusion. , 1976, The Journal of general psychology.

[12]  S J McKelvie.  Effect of psychophysical method on measurement of the Müller-Lyer illusion. , 1984, Perceptual and motor skills.

[13]  B. Lown.  Quantification of the Müller-Lyer Illusion Using Signal Detection Theory , 1988, Perceptual and motor skills.

[14]  S. Coren,et al.  A comparison of five methods of illusion measurement , 1972 .

[15]  B Bridgeman,et al.  On the origin of stroboscopic induced motion , 1983, Perception & psychophysics.

[16]  E. Wist,et al.  The scintillating grid illusion during smooth pursuit, stimulus motion, and brief exposure in humans , 2000, Neuroscience Letters.

[17]  R. B. Post,et al.  A reevaluation of the effect of velocity on induced motion , 1989, Perception & psychophysics.

[18]  F A Miles,et al.  Short latency ocular-following responses in man , 1990, Visual Neuroscience.

[19]  R. B. Post,et al.  The sum of induced and real motion is not a straight path , 1988, Perception & psychophysics.

[20]  Maarten A. Frens,et al.  Heading and path percepts from visual flow and eye pursuit signals , 2001, Vision Research.

[21]  J. Dichgans,et al.  Differential effects of central versus peripheral vision on egocentric and exocentric motion perception , 1973, Experimental Brain Research.

[22]  S. Mateeff,et al.  Dynamic Visual Capture: Apparent Auditory Motion Induced by a Moving Visual Target , 1985, Perception.