Neuroscience Letters 455 (2009) 162–167 Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Using scanning trials to assess intrinsic coordination dynamics Attila J. Kovacs, John J. Buchanan, Charles H. Shea ∗ Texas A&M University, United States article info Article history: Received 1 December 2008 Received in revised form 23 February 2009 Accepted 23 February 2009 Keywords: Perception-action Coordination dynamics Relative phase abstract Bimanual 1:1 coordination patterns other than in-phase (0 ◦ ) and anti-phase (180 ◦ ) have proven difficult to perform even with extended practice. The difficulty has been attributed to phase attraction that draws the coordination between the limbs towards the bimanual patterns of in-phase and anti-phase and variability associated with the activation of non-homologous muscles via crossed and uncrossed cortical pathways. We found participants could very effectively produce a large range of supposedly unstable coordination patterns (between 0 ◦ and 180 ◦ in 30 ◦ increments) after only 3 min of practice when integrated feedback (Lissajous plots) was provided and other perceptual and attentional distractions were minimized. These findings clearly indicate that the perception-action system is fully capable of producing a wide range of bimanual coordination patterns and that the reason for the failure to produce these patterns in previ- ous experiments reside in the perceptual information and attentional requirements typically found in experimental testing environments. © 2009 Elsevier Ireland Ltd. All rights reserved. One of the corner stones of the dynamical system perspective has been the repeated finding that bimanual coordination patterns other than in-phase ( =0 ◦ ) or anti-phase ( = 180 ◦ ) are initially unstable [22,23] and consequently hard to perform even with extended practice [3,11,19,20]. The difficulty in producing other rel- ative phase movement patterns has typically been attributed to phase attraction that draws the coordination between the limbs towards the bimanual patterns of in-phase and anti-phase (the so-called intrinsic dynamics [16]) and/or the instability associated with the activation of non-homologous muscles via crossed and uncrossed cortical pathways [9]. This pattern of results has been explained using concepts taken from nonlinear dynamics and mod- eled using nonlinearly coupled limit cycle oscillators [6] perturbed by stochastic forces [15]. The tendency for in-phase and anti-phase movements has been thought to be due to a bias originating in the action component of the perception-action system [12,13]. Clues as to the importance of perceptual information to biman- ual coordination have been found in interpersonal coordination tasks [14], where two people coordinate their movements, and uni- manual tracking tasks [1,21], whereby performers coordinate their movements to an external signal, which also exhibit stable coordi- nation patterns at 0 ◦ and 180 ◦ relative phase. In these paradigms a direct neuromuscular connection between the components was not present suggesting coupling occurs at a perceptual level [1,14,21] ∗ Corresponding author at: Department of Health and Kinesiology, Texas A&M University, College Station, TX 77843-4243, United States. Tel.: +1 979 845 5002; fax: +1 979 847 8987. E-mail address: cshea@tamu.edu (C.H. Shea). and one cannot perform what one cannot perceive [1,21]. For exam- ple, research [4] has shown that some spatial arrangements of feedback presentation allow for the integration of independent hand paths and in turn stabilize bimanual in-phase coordination, whereas others lead to increased variability. In other words, what initially is perceived as a dual task becomes a single task when the visual display allows the integration of the two tasks into a uni- fied representation. Similarly, Mechsner [12] provided compelling evidence that coordinated bimanual movements were organized in terms of perceptual symmetry and not motoric symmetry as previous work suggested. The question addressed in the present manuscript was – can par- ticipants effectively produce with low error and variability relative phase patterns between 0 ◦ and 180 ◦ typically tested in scanning blocks [22,23] with very little practice when provided salient, inte- grated feedback (Lissajous plots) and other potential perceptual and/or attentional distractions are reduced? This demonstration would clearly indicate that constraints observed in earlier 1:1 bimanual coordination experiments were attributable to percep- tual and attentional factors and not solely to motoric factors. It should be noted that Lissajous plots (named after French mathematician Jules Antoine Lissajous) have been used for some time [7] to display bimanual coordination data. More recently in attempts to provide integrated limb movement feedback in biman- ual 1:1 and polyrhythmic coordination experiments, Lissajous plots have been used to present concurrent and/or terminal feedback [3,11,18–20]. Even though the Lissajous plot as a form of feedback should be effective in integrating the movements of the two limbs, extensive practice has typically been required to effectively pro- duce a 90 ◦ relative phase movement pattern between the fingers 0304-3940/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2009.02.046