The origins of manual asymmetries, what is revealed by pushing the limits of task difficulty

Abstract

Researchers have postulated a variety of explanations for the superiority in performance of one hand over the other, many which suggest that task complexity plays an important role. However, contradictory evidence of the role of task demands has been found recently by Van Horn and McManus (1994) who have shown that difference between the hands remains constant across tasks of increasing difficulty. The purpose of the experiments reported here was to investigate the difference in performance between the hands by examining a wider range of task demands than had been previously examined. Six experiments are reported where the two hands were compared on the Annett pegboard, a Fitts' reciprocal tapping task, and the Grooved Pegboard (a standard test used in neuropsychological assessment). The difficulty of each task was varied using Fitts' Law (Fitts, 1954). It was shown that one-dimensional changes to task demands, specifically peg size, do not affect the magnitude of the performance difference between the hands. These findings replicate those of van Horn and McManus (1994). However, it was also found that an increase in the right-hand advantage occurred when multiple dimensions of task demands are examined simultaneously. The reason for this increase in the difference between the hands in perhaps due to the the experimental context and/or practice effects. In all probability, the differences in performance of the two hands reflect the organization of the underlying neural control structures.