Conference Proceedings

2004 Scottish Branch Annual Conference

Psychology in today's society
Conference Venue: Fisher's Hotel, Pitlochry
Scottish Branch

From: 26 Nov 2004
To: 28 Nov 2004

 
Peer-Reviewed

Is Action Affected by the Ponzo Illusion? Evidence for a Dissociation Between Perception and Action

L MacKay <[email]>
University of Strathclyde


It has recently been suggested that there is a neurological dissociation between perception and action in the human visual system, and that both systems use different cortical representations.  The present study investigated whether, when attentional requirements were matched between perceptual and behavioural judgements, both were affected by a visual size illusion.  In addition, maximum grip aperture (MGA) and lift forces were compared to determine whether both were affected similarly by the illusion.  Fifteen participants were asked to grasp two equally sized discs, which were made to look perceptually different in size using the Ponzo illusion, with either both hands simultaneously or one hand at a time.  Maximum acceleration and the time to lift off were used as indirect measures of the amount of force applied when lifting, and maximum grip aperture was used as a measure of the coordination of the grasp.  Despite the 3D bars in the Ponzo illusion producing an obstacle avoidance effect on maximum grip aperture, the results suggested that lift forces and MGA were programmed on the basis of two separate visual representations.  In addition, the finding that there was a reduction of both the effect of the illusion on lift forces, and of obstacle avoidance on MGA, suggested that there may be an equalising mechanism in the motor system, which serves to bring two-handed simultaneous actions closer together.  Overall, the results seem to support the idea that grasp coordination and lift forces are programmed using separate visual representations, and consequently this supports the two visual systems hypothesis.