Resource limitations in bimanual pointing.

Performing coordinated bimanual movements, that is, movements with two hands simultaneously, is a requirement in many activities. At the same time, these movements are subject to temporal and spatial constraints. Here, we focus on the constraints that become observable when pointing movements of different (asymmetric) rather than same (symmetric) amplitudes have to be executed ("spatial interference effect"). The respective performance costs are larger when the stimuli used to indicate the movement targets are symbolic compared with when the endpoints of the movements are cued directly. Previous studies have thus concluded that the source of spatial interference is both 'cognitive' and 'motoric', or more precisely occurs during response selection as well as motor programming. We here asked whether the contribution from motor programming is motoric in the sense as envisaged in dual-task models, that is, whether it can run in parallel to, and interference-free with, other processing stages. In two PRP experiments, Task 1 was bimanual pointing and Task 2 was auditory pitch-discrimination. Based on the effect propagation-logic, the results suggest that the motor programming contribution to bimanual interference also taps into capacity-limited resources and cannot be construed as running in parallel as assumed for the motor stage in dual-task models.