Attila J. Kovacs

The learning of 90° continuous relative phase with and without Lissajous feedback: external and internally generated bimanual coordination.

Results from recent experiments (e.g., Kovacs, Buchanan, & Shea, 2009a-b, 2010a,b) suggest that when salient visual information is presented using Lissajous plots bimanual coordination patterns typically thought to be very difficult to perform without extensive practice can be performed with remarkably low relative phase error and variability with 5min or less of practice. However, when this feedback is removed, performance deteriorates. The purpose of the present experiment was to determine if reducing the frequency of feedback presentation will decrease the participants reliance on the feedback and will facilitate the development of an internal representation capable of sustaining performance when the Lissajous feedback is withdrawn. The results demonstrated that reduced frequency Lissajous feedback results in very effective bimanual coordination performance on tests with Lissajous feedback available and when feedback is withdrawn. Taken together the present experiments add to the growing literature that supports the notion that salient perceptual information can override some aspects of the systems intrinsic dynamics typically linked to motor output control. Additionally, the present results suggest that the learning of both externally and internally driven bimanual coordination is facilitated by providing reduced frequency Lissajous feedback.

Perceptual and attentional influences on continuous 2:1 and 3:2 multi-frequency bimanual coordination.

Two experiments were conducted to determine if multi-frequency (2:1 and 3:2) coordination between the limbs is enhanced when integrated feedback is provided in the form of Lissajous plots, attention demands are reduced, and attempts to consciously coordinate the limbs are not encouraged. To determine the influence of vision of the limbs, covered and uncovered limb groups were provided online Lissajous feedback. To determine the impact of the Lissajous feedback, a control group that was not provided Lissajous feedback was also tested. The data indicated remarkably effective performances after 5 min of practice when limbs were covered and Lissajous feedback was provided. When Lissajous feedback was provided and vision of the limbs was permitted, performance deteriorated. Performance by the group not provided Lissajous feedback was quite poor. The findings suggest that some of the difficulty associated with producing difficult bimanual coordination patterns are due to the less than optimal perceptual information available in various testing situations and the attentional focus imposed by the participant.

The coding and effector transfer of movement sequences

Three experiments utilizing a 14-element arm movement sequence were designed to determine if reinstating the visual-spatial coordinates, which require movements to the same spatial locations utilized during acquisition, results in better effector transfer than reinstating the motor coordinates, which require the same pattern of homologous muscle activation. Results demonstrated better transfer when visual-spatial coordinates were reinstated than when motor coordinates where reinstated regardless of the amount of practice (1, 4, or 12 days; Experiments 1-3, respectively). Transfer (left to right and right to left) was symmetric when visual-spatial coordinates were reinstated but not when motor coordinates were reinstated. When motor coordinates were reinstated after 12 days of practice and vision occluded, transfer was better from right limb to left than vice versa. The data are also consistent with the notion that multiple codes (visual, spatial, and motor) are developed over practice, with each contributing to transfer performance when the respective coordinates are reinstated. Further, the results indicate a disruption of the linkage (concatenation) between subsequences when one or more coordinates are changed on the transfer test.

The Coding and Inter-Manual Transfer of Movement Sequences

The manuscript reviews recent experiments that use inter-manual transfer and inter-manual practice paradigms to determine the coordinate system (visual–spatial or motor) used in the coding of movement sequences during physical and observational practice. The results indicated that multi-element movement sequences are more effectively coded in visual–spatial coordinates even following extended practice, while very early in practice movement sequences with only a few movement elements and relatively short durations are coded in motor coordinates. Likewise, inter-manual practice of relatively simple movement sequences show benefits of right and left limb practice that involves the same motor coordinates while the opposite is true for more complex sequences. The results suggest that the coordinate system used to code the sequence information is linked to both the task characteristics and the control processes used to produce the sequence. These findings have the potential to greatly enhance our understanding of why in some conditions participants following practice with one limb or observation of one limb practice can effectively perform the task with the contralateral limb while in other (often similar) conditions cannot.

Inter-manual transfer and practice: Coding of simple motor sequences

Previous research suggests that movements are represented early in practice in visual-spatial coordinates/codes, which are effector independent, and later in practice in motor coordinates/codes (e.g., joint angles, activation patterns), which are effector dependent. In the present experiments, the task was to reproduce 1.3 s patterns of elbow flexions and extensions. An inter-manual transfer paradigm was used in Experiment 1 and an inter-manual practice paradigm was used in Experiment 2. The present results clearly indicated a strong advantage of effector transfer when the motor coordinates available during acquisition were reinstated (Experiment 1) and demonstrate that inter-manual practice with the same motor coordinates results in enhanced retention performance relative to transfer and practice where the same visual-spatial coordinates are used. These results demonstrate that the more effective movement code (motor or visual-spatial) is dependent on the movement sequence characteristics (e.g., difficulty, number of elements, and mode of control [preplanned or on-line]). These results are also interesting because they indicate, contrary to previous findings with more complex movement sequences, that an effective motor code can be developed relatively early in practice for rapid movement sequences.

Perceptual influences on Fitts' law.

The linear relationship between movement time (MT) and index of difficulty (ID) for Fitts’ type tasks has proven ubiquitous over the last 50+ years. A reciprocal aiming task (IDs 3, 4.5, 6) was used to determine if an enlarged visual display (visual angle 5.1°, 7.4°, or 13.3°) would alter this relationship. With ID = 6, a condition typically associated with discrete action control, the largest visual display (13.3°) allowed the motor system to exploit features of cyclical action control, e.g., shorter dwell times, more harmonic motion, less time decelerating the limb. The large visual display resulted in a quadratic relationship between MT and ID. For the IDs of 3 and 4.5, the visual displays did not alter the underlying control processes. The results are discussed in terms of the preference of the motor system to assemble movements from harmonic basis functions when salient visual information is provided.

Using scanning trials to assess intrinsic coordination dynamics.

Bimanual 1:1 coordination patterns other than in-phase (0 degrees ) and anti-phase (180 degrees ) 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 degrees and 180 degrees in 30 degrees 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 previous experiments reside in the perceptual information and attentional requirements typically found in experimental testing environments.

Representation of movement sequences is related to task characteristics

Recent experiments have produced mixed results in terms of performance when, after learning a sequential task, the same visual-spatial coordinates or the same motor coordinates were reinstated on a subsequent effector transfer test. Given the diversity of tasks and especially sequence characteristics used in previous experiments, the cross-experimental comparison makes inferences and unambiguous interpretations difficult. The purpose of the present experiment was to determine in a principled manner how the spatio-temporal structure of a sequence influences the way the sequence is represented. The results indicated that after limited amount of practice relatively more simple sequences (S1) are coded more efficiently in a mirror (motor) representation which requires the same pattern of homologous muscle activation. Conversely, relatively more complex sequences (S2) are more efficiently coded in a visual-spatial coordinate system which requires movements to the same spatial locations as during acquisition. The data are also consistent with the notion that sequences with different spatio-temporal structures rely to a different degree on distinct control mechanisms (pre-planned vs. on-line, respectively).

Coding of on-line and pre-planned movement sequences

Recent experiments have demonstrated that complex multi-element movement sequences were coded in visual-spatial coordinates even after extensive practice, while relatively simple spatial-temporal movement sequences are coded in motor coordinates after a single practice session. The purpose of the present experiment was to determine if the control process rather than the difficulty of the sequence played a role in determining the pattern of effector transfer. To accomplish this, different concurrent feedback conditions were provided to two groups of participants during practice of the same movement sequence. The results indicated that when concurrent visual feedback was provided during the production of the movement, which was thought to encourage on-line control, the participants performed transfer tests with the contra-lateral limb better when the visual-spatial coordinates were reinstated than when the motor coordinates were reinstated. When concurrent visual feedback was not provided, which was thought to encourage pre-planned control, the opposite was observed. The data are consistent with the hypothesis that the mode of control dictates the coordinate system used to code the movement sequence rather than sequence difficulty or stage of practice as has been proposed.

Bimanual Fitts’ tasks: Kelso, Southard, and Goodman, 1979 revisited

The experiment was designed to replicate and extend to an integrated feedback condition the pattern of movement time results found by Kelso et al. (J Exp Psychol Hum Percept Perform 5:229–238, 1979a, Science 204:1029–1031, 1979b) where the simultaneous movement of one hand to a low ID target and the other to a higher ID target indicated “a tight coordinate coupling between the hands” (p. 229). In the present experiment, a control group was provided feedback that depicted the independent movement of the two limbs under low and higher indexes of difficulty (ID). A Lissajous group was provided integrated feedback in the form of a Lissajous plot. The results indicated a pattern of results for the control and Lissajous groups similar to that found by Kelso et al. for one and two-limb movements to the same difficulty targets. The control group also replicated the finding for two-limb movements to mixed ID tasks. However, the Lissajous group simultaneously produced disparate movement in the mixed target conditions. The results are consistent with recent findings indicating that when provided salient integrated feedback participants can effectively produce disparate movements of the two limbs.