Tactile perceptual asymmetry: the influence of motor activity and imagery instructions

The purpose of this study was to examine the degree to which changes in muscular activity modify tactile perceptual asymmetries. In two experiments subjects were presented with a series of pairs of random shapes to the fingers of each hand. Their task was to detect the occurrence of a previously learnt target shape. Pressing on to the shape was the only movement allowed and other types of motor activity, particularly tracing movements, were not permitted. Across experimental conditions subjects were required to change the pressure and hence muscular effort used to press upon the shape. A left-hand advantage was found across all experimental conditions and its size did not change when subjects were required to press either firmly or lightly upon the shapes. This result was also found when subjects were required to apply uneven pressure between the hands. One-half of the subjects also performed the experimental conditions following instructions to use imagery. This produced an enhancement of right-hand performance on the task with a loss of the left-hand advantage. The results suggest that observed tactile perceptual asymmetries, while unaffected by changes in muscular effort, are easily overridden by higher-order cognitive and motor processes.