Abstract
The usual means of describing bilateral transfer quantitatively is to measure a response for the modality of interest on one side of the midline (e.g., left arm, left eye, etc.) as a baseline condition, and in a separate condition measure the same response following (or simultaneous with) activity with the same modality on the other side of the midline as a bilateral condition. The deviation of the response in the bilateral condition from the baseline condition divided by the difference between the unilateral responses on the two sides provides the usual measure of % transfer. We show that the % transfer measure is mathematically identical to a linear weighted average of the unilateral responses from the two sides of the midline and that this leads to a decrease in the slope of the function relating the original unilateral response-vs-a-critical stimulus parameter. We have measured manual heightmatching to a visual target in darkness whose perceived elevation is systematically influenced by the pitch of a single eccentrically located line, and also systematically influenced by the distance of the hand from the body. The connection between the % transfer and the slope of the manual heightmatch-setting-vs-hand-to-body distance function noted above was found to hold. This supports a linear weighted average model for bimanual heightmatching. The ecological significance of such bilateral averaging will be described. This significance is general for many bilateral functions beyond the manual heightmatching for which we found it to hold, and suggests that experimental tests of other bilateral functions would provide similar agreement with the linear weighted average model.
Supported by NSF grant BCS-06-16654.