An event-based account of coordination stability

Constraints underlying bimanual coordination have traditionally been explained by dynamic interactions between the effectors. However, the present experiments demonstrate that a fundamental constraint on bimanual performance is the manner in which task goals are represented. In Experiment 1, participants vocalized during in-phase and anti-phase bimanual movements. As expected, most participants spontaneously exhibited temporal coupling between the manual and vocal responses. However, the form of coupling differed for the in-phase and anti-phase conditions. For anti-phase movements, there was a strong bias to produce two vocalizations per cycle; for in-phase movements, participants were equally likely to produce one or two vocalizations per cycle. We hypothesized that the spontaneous vocalizations probed the cognitive representation of the task, and the results indicated that anti-phase movements did entail a more complex event structure than in-phase movements did. In Experiment 2, we manipulated the event structure by having participants vocalize either once or twice per hand cycle. As predicted, coordination stability was reduced when the event structure was more complex.     

Planning and timing of finger-tapping sequences with a stressed element

Advance planning and execution-time organization of sequences of five finger taps were studied in four experiments. Intertap intervals were required to be equal. In some experimental conditions, one of the taps had to be stronger than the other four. Serial position of the stressed tap, number of alternative stress positions, and tapping rate were manipulated. Time to initiate the sequence after presentation of a reaction stimulus (RT), intertap intervals, and force of the taps were measured. the different effects of stress production and choosing between alternative stress locations on the RT of fast as compared to slow sequences suggest that a plan was selected and activated for the whole sequence only when it had to be executed at a fast rate. Additional organization of the fast sequences during execution was inferred from the intertap intervals, force patterns, and stress location errors, that were all different from those observed in slow sequences. The effects of stress production on timing are discussed in relation to existing timing models.     

Le geste approprié au juste moment : faut-il une horloge pour que le mouvement soit dans les temps ?

The movement of a body is defined as a variation of its position in time (dx/dt). However, referring to time to describe a movement does not imply that the production of a biological movement necessitates an explicit control of the temporal parameters, and even less that such a control has to be performed with the help of a clock. In this review of the literature, we will try to show, through an analysis of the protocols used, that the answer to this question critically depends on the motor task to be performed. Possible directions towards a convergence will be proposed.     

The Dynamics of Bimanual Circle Drawing

A bimanual circle drawing task was employed to elucidate the dynamics of intralimb and interlimb coordination. Right-handed subjects were required to produce circles with both hands in either a symmetrical (mirror) mode (i.e. one hand moving clockwise, the other counter-clockwise) or in an asymmetrical mode (i.e. both hands moving clockwise or counter-clockwise). The frequency of movement was scaled by an auditory metronome from 1.50 Hz to 3.25 Hz in8 (8-sec) steps.In the asymmetrical mode,distortions ofthe movement trajectories, transient departures from the target pattern of coordination, and phase wandering were evident as movement frequency was increased. These features suggested loss of stability. Deviations from circular trajectories were most prominent for movements of the left hand. Transient departures from the required mode of coordination were also largely precipitated by the left hand. The results are discussed with reference to manual asymmetries and mechanisms of interlimb and intersegmental coordination.