Bimanual reaches with symbolic cues exhibit errors in target selection

We examined symmetric and asymmetric bimanual reaches to targets specified by direct spatial cues and by indirect symbolic cues. Symbolically-cued asymmetric reaches have been shown to exhibit longer reaction times (RTs) compared to symmetric reaches, whereas no such RT cost is observed when targets are directly cued – a pattern thought to implicate increased demands on response selection (Diedrichsen et al., 2001). Assuming that symbolically-cued reaches engage intentional control whereas directly-cued reaches engage more automatic visuo-motor control mechanisms, we asked whether bimanual movements exhibit more interference with symbolic cues than with spatial cues. Participants made bimanual symmetric and asymmetric reaches to short- and long-distance targets cued either symbolically or spatially. We replicated the reaction time cost for symbolically-cued asymmetric movements. A subset of these asymmetric reaches also showed large trajectory corrections. It appeared that this subset had been incorrectly prepared and the movements required of the left and right hands had been switched. No such errors in reach selection were observed when targets were directly cued. In contrast to the RT cost and errors in selection for symbolically-cued movements, we observed little evidence of interference once movements were initiated and executed toward the correct targets regardless of the type of cue.