Hand–head coordination changes from discrete to reciprocal hand movements for various difficulty settings

Abstract

The parameters dictating the temporal hand–head coordination during visually corrected movements remain elusive. Here we examine the effects of the nature (discrete vs reciprocal) and the difficulty (ID of 4.7, 5.7 and 6.7 bits) of the task on the temporal hand–head coordination during a Fitts’ like paradigm. Subjects aimed at a single target (discrete movement) or alternately to two targets (reciprocal movements). Head movements were unaffected by the ID during discrete movements. This was not the case during reciprocal movements where they were (1) smaller in duration and amplitude than during discrete movements and (2) increased in duration and amplitude with an increasing ID. To measure the temporal hand–head coordination, hand–head latencies were calculated at the onset, peak speed and offset of each movement. Offset latencies remained positive (i.e. the hand reached the target after the head stopped) for all IDs during reciprocal but not during discrete movements. Altogether, different patterns of temporal hand–head coordination were observed between discrete and reciprocal movements as well as between IDs, suggesting the hand–head coordination does not follow a fixed rule but is adjusted to task requirements.