Rhythmic limb movements are often anchored at particular points in the movement cycle. Anchoring may reveal essential task-specific information for motor control. We examined the effect of tracking mode (in-phase, antiphase) and gaze direction (left, right) on anchoring in visuomotor tracking with and without concurrent visual feedback of the hand movement. For in-phase tracking, anchoring was observed at the foveated reversal point whereas for antiphase tracking anchoring was observed at both reversals, suggesting the presence of two reference points instead of one. Anchoring at the foveated reversal reflected gaze anchoring (i.e., coalignment of hand and gaze) while anchoring at the nonfoveated reversal reflected visuomotor synchronization (i.e., the hand was steered to the nonfoveated reversal coincident with a target reversal at the point of gaze). We propose that the number and location of anchor points play a crucial role in the underlying control by providing reference values for error correction processes.
Melvyn Roerdink, Paulina J. M. Bank, C. (Lieke) E. Peper and Peter J. Beek
Betteco J. de Boer, C. (Lieke) E. Peper and Peter J. Beek
Developmental changes in bimanual coordination were examined in four age groups: 6/7, 10/11, 14/15 years, and young adults. Temporal coupling was assessed through the stabilizing contributions of interlimb interactions related to planning, error correction, and reflexes during rhythmic wrist movements, by comparing various unimanual and bimanual tasks involving passive and active movements. Spatial coupling was assessed via bimanual line-circle drawing. With increasing age, temporal stability improved. Relative contributions of planning and reflex interactions to the achieved stability did not change, whereas error correction improved. In-phase and antiphase coordination developed at similar rates; implications of this result were discussed in terms of mirror-activity inhibition. Overall spatial drawing performance (circularity, variability, smoothness) improved with age, and spatial interference was smaller in adults than children. Whereas temporal coupling increased from 6/7 years to adulthood, spatial coupling changed mainly after 14/15 years. This difference in the development of temporal and spatial coupling corresponds to the anterior-posterior direction of corpus callosum myelination as reported in the literature.
Betteco J. de Boer, C. (Lieke) E. Peper, Arne Ridderikhoff and Peter J. Beek
In the current study, we examined whether coupling influences resulting from unintended afference-based phase entrainment are affected by movement amplitude as such or by the amplitude relation between the limbs. We assessed entrainment strength by studying how passive movements of the contralateral hand influenced unimanual coordination with a metronome. Results showed that amplitude as such did not affect entrainment strength, whereas the amplitude relation between the hands did. Larger amplitudes of the passive hand relative to the active hand resulted in stronger entrainment. This dependence on relative amplitude implies that entrainment strength is not only based on the intensity of afferent signals generated in the entraining limb but also on the susceptibility of the entrained limb to these signals.