Neuroscience Letters 521 (2012) 1–5 Contents lists available at SciVerse ScienceDirect Neuroscience Letters jou rn al h om epage: www.elsevier.com/locate/neulet Hand–head coordination changes from discrete to reciprocal hand movements for various difficulty settings Mathieu Germain-Robitaille a,b , Romain Terrier c , Nicolas Forestier c , Normand Teasdale a,b,∗ a Division de Kinésiologie, Département de Médecine Sociale et Préventive, Faculté de Médecine, Université Laval, Québec, Québec G1K 7P4, Canada b Vieillissement, Centre de recherche du CHA, Canada c Laboratoire de Physiologie de l’Exercice (E.A. 4338), Département STAPS, UFR CISM, Université de Savoie, 73376 Le Bourget du lac cedex, France h i g h l i g h t s ◮ Head movement amplitude and duration is modified by task nature and difficulty. ◮ Hand–head coordination adapts to task difficulty and nature. ◮ No hand–head main sequence is optimal during discrete movements. a r t i c l e i n f o Article history: Received 16 January 2012 Received in revised form 9 March 2012 Accepted 30 April 2012 Keywords: Hand Head Coordination Reciprocal Pointing Difficulty a b s t r a c t 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 move- ments). 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 dis- crete 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 pat- terns 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. Crown Copyright © 2012 Published by Elsevier Ireland Ltd. All rights reserved. 1. Introduction Fitts’ law [7] states that the time needed to point to a target as fast and as accurately as possible increases linearly with an index of difficulty defined as the log 2 (2A/W) where A is the amplitude of the movement and W is the width of the target. Fitts’ law has been verified for different contexts and tasks [16]. For instance, the head has been used as the effector for pointing movements, either by extension with a laser pointer [5,10] or through a computer input device (e.g. when using a head tracker for moving a pointer on a screen) [14,15]. Generally, however, the head is the moving base of the visual and vestibular sensors for other effectors such has the ∗ Corresponding author at: 2300, rue de la Terrasse, Département de kinésiologie, Faculté de Médecine, Université Laval, Québec, Québec G1V 0A6, Canada. Tel.: +1 418 656 2147; fax: +1 418 656 2441. E-mail address: Normand.Teasdale@kin.ulaval.ca (N. Teasdale). finger, the wrist or the arm [9,12] and in some rare cases the foot [2]. Using a discrete pointing task, Biguer et al. [3] observed that the amplitude of the head never exceeded 2/3 of the distance sepa- rating two targets. These authors were also the first to report that immobilizing the head reduces pointing accuracy for target eccen- tricity over 30 ◦ . Similar results were obtained by Bard et al. [1] for their head movers group in contrast with their non head movers group whose accuracy remained unaffected by target eccentric- ity up to 45 ◦ . In line with these observations, Rossetti et al. [17] showed that hand pointing variability was reduced when head movements, rather than eye movements, contributed to local- izing the target. Presumably, head movements improve spatial localization accuracy by allowing the eyes to come back to their optimal working zone once the initial saccade is completed [17]. Interestingly, when hand and head movements are made follow- ing a signal to move as rapidly and as accurately as possible, the head slows down compared to normal eye–head saccades (without 0304-3940/$ – see front matter. Crown Copyright © 2012 Published by Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neulet.2012.04.074