Reflecting upon vision: The limited effects of visual feedback upon motor output in a bimanual tapping task.
Iveson Matthew Dissertation 2009.doc (341Kb)
MetadataShow full item record
Whilst previous studies have focused on the importance of other sensory information, the use of mirrors has been instrumental in investigating the contribution of visual feedback to motor output. Franz and Packman (2004) recently demonstrated that vision of a hand facilitates the convergence of each hand’s movement characteristics upon each other. The present study attempted to replicate this finding in a bimanual continuation task, which involved the in-phase and anti-phase tapping of the index fingers. Seventeen right-handed participants were recruited in experiment one, and twelve right-handed participants were recruited in experiment two. Normal, full vision was given in certain conditions, whilst others involved the control of vision. In the first experiment, a mirror was placed either centrally or to the side, to manipulate the available visual feedback, with the illusion of symmetrical movement of the left and right hands particularly relevant in the anti-phase task. In the second experiment only the central mirror and the normal viewing conditions were used, but tactile feedback was reduced further by employing contact-free tapping movements. A greater tendency towards in-phase movement between the hands was predicted in the central mirror condition during the anti-phase task as the output of the hands became similar. However, even when tactile and auditory feedback was reduced, no evidence of bimanual coupling was found. Indeed, both hands performed well under all visual conditions, with very little deviation from the relevant phase observed. This was taken to indicate that vision plays a limited role in motor output, and that successful bimanual coordination can occur without veridical feedback. Indeed, the use of mirrors is unable to trick the systems that underlie motor output in a simple task. Instead, the effects of attention may account for the findings of both the present study and those of Franz and Packman (2004). Both circle radii (Franz, 2003) and the performance of the non-dominant hand (Swinnen, Jardin, and Meulenbroek, 1996) have been shown to be affected in bimanual tasks by the manipulation of attention. This leads the present study to the conclusion that mirrors may mask the impact of attention in the guise of visual effects. Consequently, the present study argues caution when implementing mirror techniques in future studies.