The Tapley and Bryden test of performance differences between the hands: The original data, newer data, and the...

Tapley and Bryden (T&B)'s 1985 circle-marking task is a group-administered task assessing performance differences between the hands. The bimodal distribution clearly separates self-described right- and left-handers. Using Phil's original datafiles we analyse the test in more detail, providing raw scores for each hands which are useful forensically, and we provide reliability estimates. Van Horn's unpublished 1992 PhD thesis studied T&B tasks and Annett pegboards varying in difficulty. A striking finding, that Phil Bryden called "the Van Horn problem," was that hand differences (R - L) were unrelated to task difficulty. That result was the starting point for Pamela Bryden's 1998 thesis, firstly replicating Van Horn, but then showing that task difficulty did relate to hand differences for Grooved pegboards. Pamela Bryden's model for those effects is presented here. Comparing across tasks, the T&B and pegboard tasks showed almost complete consistency for direction of handedness. Likewise, within each task, degree of handedness intercorrelated strongly across variants. In strong contrast, degree of handedness for T&B tasks showed minimal correlation with degree of handedness for pegboards. At the highest level, therefore, direction of handedness is consistent within individuals (conventional right and left handedness), but there are separable processes determining dominant-non-dominant hands differences for each particular task.