Sequential motor ability of left-handed inverted and non-inverted writers.

Left-handed female subjects, categorized as using an inverted (LI) (n=7) or non-inverted (LN) (n=7) writing posture, were compared on performance of a motor task. Task parameters were manipulated to create four conditions varying in demand for sequential processing. Based on previously observed group differences in the direction and extent of hemispheric lateralization, non-inverted writers were predicated to exhibit superior left hand performance. An analysis of variance substantiated a performance superiority by the LN writers, however, post hoc analysis indicated the difference to exist only at the highest level of task difficulty. Analysis of right-hand performance revealed a significant group difference in favor of the LN writers and a group-by-sequential processing demand interaction. This interaction indicated that the decrement in performance of LI writers, relative to LN writers, increased systematically with increases in task demands for sequential processing. Since previous research indicated that inverted writers exhibit less hemispheric specialization of function, it is concluded that this bilateral representation is associated with an overall reduction in sequential processing ability.