Multilevel coordination stability: integrated goal representations in simultaneous intra-personal and inter-agent coordination

The influence of integrated goal representations on multilevel coordination stability was investigated in a task that required finger tapping in antiphase with metronomic tone sequences (inter-agent coordination) while alternating between the two hands (intra-personal coordination). The maximum rate at which musicians could perform this task was measured when taps did or did not trigger feedback tones. Tones produced by the two hands (very low, low, medium, high, and very high) could be the same as, or different from, one another and the (medium-pitched) metronome tones. The benefits of feedback tones were greatest when they were close in pitch to the metronome and the left hand triggered low tones, while the right hand triggered high tones. Thus, multilevel coordination was facilitated by tones that were easy to integrate with, but perceptually distinct from, the metronome, and by compatibility of movement patterns and feedback pitches.     

Dual-Finger Preferred-Speed Tapping: Effects of Coordination Mode and Anatomical Finger and Limb Pairings

Interlimb and interfinger coordination were examined in a dual-finger tapping paradigm in which 16 subjects performed at preferred frequencies. Three bimanual finger combinations, in random order (2 index; 2 middle; and 1 index and 1 middle), were performed in in-phase and antiphase coordination modes, in addition to 1 unimanual combination (antiphase index-middle). Relative phase means were within 3&percent; accuracy for all conditions. A lower tapping frequency was found in all antiphase vs. in-phase conditions, accompanied by lower phasing variability and lower intrafinger consistency in the antiphase. When frequency was changed from the preferred rate, the 2 coordination modes became more alike in variability and, within the same frequency range, demonstrated no significant differences. The bimanual mixed-fingers tapping tended to have significantly lower phasing values (a small fixed point drift) and higher tapping frequencies than the symmetric conditions. The unimanual task was similar to all other antiphase conditions. Changes in preferred frequency with different coordination modes may be related to differing perceptual informational constraints. Current models addressing natural frequencies of coupled oscillators do not account for the present data.     

Asymmetric control of force and symmetric control of timing in bimanual finger tapping

An experiment was conducted to examine the control of force and timing in bimanual finger tapping. Participants were trained to produce both unimanual (left or right hand) and bimanual finger-tapping sequences with a peak force of 200 g and an intertap interval (ITI) of 400 ms. During practice, visual force feedback was provided pertaining to the hand performing the unimanual tapping sequences and to either the dominant or the nondominant hand in the bimanual tapping sequences. After practice, the participants produced the learned unimanual and bimanual tapping sequences in the absence of feedback. In those trials the force produced by the dominant (right) hand was significantly larger than that produced by the nondominant (left) hand, in the absence of a significant difference between the ITIs produced by both hands. Furthermore, after unilateral feedback had been provided of the force produced by the nondominant hand, the force output of the dominant hand was significantly more variable than that of the nondominant hand. In contrast, after feedback had been provided of the force produced by the dominant hand, the variability of the force outputs of the two hands did not differ significantly. These results were discussed in the light of both neurophysiological and anatomical findings, and were interpreted to imply that the control of timing (in bimanual tasks) may be more tightly coupled in the motor system than the control of force.     

Impact of Handedness Consistency on Bimanual and Unimanual Continuous Movements

Bimanual coordination is an essential human function requiring efficient interhemispheric communication to produce coordinated movements. Previous research suggests a “bimanual advantage” phenomenon, where completing synchronized bimanual tasks results in less variability than unimanual tasks. Additionally, of hand dominance has been shown to influence coordinated performance. The present study examined the bimanual advantage in individuals with consistent and inconsistent handedness. It was predicted that participants with consistent handedness would not display a bimanual advantage unlike those with inconsistent handedness. Fifty-six young adults completed a finger-tapping paradigm in five conditions: unimanual tapping with either left or right hand, in-phase bimanual tapping, and out-of phase bimanual tapping led by either left or right hand. Results were not consistent with the hypothesis that participants with consistent handedness displayed the “bimanual advantage”. However, the “bimanual advantage” was not evident for the inconsistent handers when the temporal consistency was measured with either the left or right hand only. Overall, the “bimanual advantage” may be dependent upon consistency of hand preference, as well as the direction of hand dominance.     

Bimanual interference in children performing a dual motor task

The present study addressed the development of bimanual interference in children performing a dual motor task, in which each hand executes a different task simultaneously. Forty right-handed children (aged 4, 5-6, 7-8 and 9-11years, ten in each age group) were asked to perform a bimanual task in which they had to tap with a pen using the non-preferred hand and simultaneously trace a circle or a square with a pen using the preferred hand as quickly as possible. Tapping and tracing were also performed unimanually. Differences between unimanual and bimanual performance were assessed for number of taps, length of tap trace and mean tracing velocity. It was assumed that with increasing age, better bimanual coordination would result in better performance on the dual task showing less intermanual interference. The results showed that tapping and tracing performance increased with age, unimanually as well as bimanually, consistent with developmental advancement. However, the percentage of intermanual interference due to bimanual performance was not significantly different in the four age groups. Although performing the dual task resulted in mutual intermanual interference, all groups showed a significant effect of tracing shape. More specifically, all age groups showed a larger percentage decrease in tracing velocity when performing the circle compared to the square in the dual task. The present study reveals that children as young as four years are able to coordinate both hands when tapping and tracing bimanually.     

Reduced timing variability during bimanual coupling: A role for sensory information

On a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with two hands as compared to one-hand tapping. Because this bimanual advantage can be attributed to timer variance (Wing-Kristofferson model, 1973a, b), separate timers have been proposed for each hand, whose outputs are then averaged (Helmuth & Ivry, 1996). An alternative notion is that action timing is based on its sensory reafferences (Aschersleben & Prinz, 1995; Prinz, 1990). The bimanual advantage is then due to increased sensory reafference. We studied bimanual tapping with the continuation paradigm. Participants first synchronized their taps with a metronome and then continued without the pacing signal. Experiment 1 replicated the bimanual advantage. Experiment 2 examined the influence of additional sensory reafferences. Results showed a reduction of timer variance for both uni- and bimanual tapping when auditory feedback was added to each tap. Experiment 3 showed that the bimanual advantage decreased when auditory feedback was removed from taps with the left hand. Results indicate that the sensory reafferences of both hands are used and integrated into timing. This is consistent with the assumption that the bimanual advantage is at least partly due to the increase in sensory reafference. A reformulation of the Wing-Kristofferson model is proposed to explain these results, in which the timer provides action goals in terms of sensory reafferences.     

Unilateral vs. bilateral coordination of circle-drawing tasks

The number of joint motions available in the upper extremity provides for multiple solutions to the coordination of a motor task. Making use of these abundant joint motions provides for task flexibility. Controlling bimanual movements poses another level of complexity because of possible tradeoffs between coordination within a limb and coordination between the limbs. We examined how flexible patterns of joint coordination were used to stabilize the hand's path when drawing a circle independently compared to a bimanual pattern. Across-trial variance of joint motions was partitioned into two components: goal-equivalent variance (GEV), representing variance of joint motions consistent with a stable hand path and non-goal-equivalent variance (NGEV) representing variance of joint motions that led to deviations of the hand's path. GEV was higher than NGEV in both unimanual and bimanual drawing, with one exception. Both GEV and NGEV, related to control of the individual hands' motion, decreased when engaged in the bimanual compared to unimanual drawing. Moreover, NGEV, leading to variability in the vectorial distance between the hands, was higher when the two hands drew circles in a bimanually asymmetric vs. symmetric pattern, consistent with reported differences in the relative phasing of the two hands. Our results suggest that the nervous system controls the individual hands' motions by separate intra-limb synergies during both unimanual and bimanual drawing, and superimposes an additional synergy to achieve stable relative motion of the two hands during bimanual drawing.     

Bimanual Lifting: Do Fingertip Forces Work Independently or Interactively?

Bimanual coordination is a commonplace activity, but the consequences of using both hands simultaneously are not well understood. The authors examined fingertip forces across 4 experiments in which participants undertook a range of bimanual tasks. They first measured fingertip forces during simultaneous lifts of 2 identical objects, noting that individuals held the objects with more force bimanually than unimanually. They then varied the mass of the objects held by each hand, noting that when both hands lifted together performance was equivalent to unimanual lifts. The authors next measured one hand's static grip force while the other hand lifted an object. They found a gradual reduction of grip force throughout the trial, but once again no evidence of one hand influencing the other. In the final experiment the authors tested whether tapping with one hand could influence the static grip force of its counterpart. Although the authors found no changes in static grip force as a direct consequence of the other hand's actions, they found clear differences from one task to the other, suggesting an effect of task instruction. Overall, these results suggest that fingertip forces are largely independent between hands in a bimanual lifting context, but are sensitive to different task requirements.     

The contribution of tactile reafference to temporal regularity during bimanual finger tapping

In a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with both hands, as opposed to single-handed tapping. This bimanual advantage can be attributed to timer variance (according to the Wing-Kristofferson model). Separate timers have been proposed for each hand whose outputs are then averaged (Helmuth & Ivry, 1996, Journal of Experimental Psychology: Human Perception and Performance, 22, 278-293). Alternatively, timing might be based on sensory reafference and the bimanual advantage due to the enhancement of sensory reafferences. This alternative hypothesis was tested in three experiments. In the first experiment, we replicated the bimanual advantage in tapping with two fingers of the same hand compared with single finger tapping. In the second experiment, we demonstrated that the bimanual advantage decreased when tactile reafferences from left-hand taps were omitted (by contact-free tapping). In the third experiment, participants tapped bimanually with the index fingers of both hands firmly mechanically coupled. The bimanual advantage was replicated for this condition. Results are consistent with the assumption that the bimanual advantage is due to the sensory reafferences of the second hand. We suggest that our results are best explained by a reformulation of the Wing-Kristofferson model, in which the timer provides action goals in terms of sensory reafferences.     

Subcortical locus of temporal coupling in the bimanual movements of a callosotomy patient

The timing of repetitive movements was assessed in a callosotomy patient under unimanual and bimanual conditions. Similar to neurologically healthy individuals, the patient exhibited strong temporal coupling in the bimanual condition. Moreover, for both the left and right hands, within-hand temporal variability was reduced in the bimanual condition compared to the unimanual conditions. This bimanual advantage is hypothesized to reflect the temporal integration of separable timing signals, one associated with the left hand and one associated with the right hand (Helmuth, L. L., & Ivry, R. B. (1996). When two hands are better than one: Reduced timing variability during bimanual movements. Journal of Experimental Psychology: Human Perception and Performance, 2, 278–293). The fact that it persists following callosotomy is inconsistent with models that attribute bimanual coordination in these patients to the control of a single hemisphere. Rather, the results suggest that motor commands from the two hemispheres are integrated subcortically.PsychINFO Classification: 2330; 2340; 2520     

The coupled oscillator model of between-hand coordination in alternate-hand tapping: a reappraisal

Single and alternating hand tapping were compared to test the hypothesis that coordination during rhythmic movements is mediated by the control of specific time intervals. In Experiment 1, an auditory metronome was used to indicate a set of timing patterns in which a 1-s interval was divided into 2 subintervals. Performance, measured in terms of the deviation from the target patterns and variability, was similar under conditions in which the finger taps were made with 1 hand or alternated between the 2 hands. In Experiment 2, the modality of the metronome (auditory or visual) was found to influence the manner in which the produced intervals deviated from the target patterns. These results challenge the notion that bimanual coordination emerges from coupling constraints intrinsic to the 2-hand system. They are in accord with a framework that emphasizes the control of specific time intervals to form a series of well-defined motor events.     

Effects of learning and movement frequency on polyrhythmic tapping performance

This study examined the effect of learning a complex bimanual coordination task at different movement frequencies. 30 subjects performed 5:3 polyrhythmic tapping at either high, medium, or low movement frequency on a rhythmic synchronization task and then reproduced the polyrhythmic pattern repeatedly in the spontaneous task. Analysis showed that practice on the synchronization task qualitatively changed correct responses into anticipatory ones. The synchronization learning of the polyrhythm caused the anticipatory responses and so, may involve memorization of serial positions within the polyrhythm. Also, more anticipatory responses were indicated in performance at the medium and low frequencies than at the high frequency on the synchronization task. In addition, deviations of taps from expected tapping positions were observed in performance of the spontaneous task at the high frequency. These results suggest that the movement frequency qualitatively influenced the learning of this bimanual coordination. Especially at the high frequency, frequent shifts to other coordination patterns occurred on the spontaneous task. This means that the performance at higher frequency is more strongly affected by entrainment between the two hands.     

Roles of Visual Information for Control of Reaching Movements in Children

Poststroke hemiparetic individuals (n = 9) and a control group (n = 9) completed a frequency-scaled circle-drawing task in unimanual and bimanual conditions. Measures of intralimb spatial and temporal task accuracy and interlimb coordination parameters were analyzed. Significant reductions in task performance were seen in both limbs of the patients and controls with the introduction of bimanual movement. Spatial performance parameters suggested that the 2 groups focused on different hands during bimanual conditions. In the controls, interlimb coordination variables indicated predictable hand dominance effects, whereas in the patient group, dominance was influenced by the side of impairment and prior handedness of the individual. Therefore, in this particular bimanual task, performance improvements in the hemiplegic side could not be elicited. Intrinsic coupling asymmetries between the hands can be altered by unilateral motor deficits.     

Distinct ways of timing movements in bimanual coordination tasks: contribution of serial correlation analysis and implications for modeling

Bimanual coordination dynamics have been conceived as the outcome of a global coordinative system, and coordination stability properties and theories of underlying processes have often been generalized over various bimanual tasks. In unimanual timing tasks it has been shown that different timing processes are involved according to tasks, yielding distinctive correlation properties in the within-hand temporal patterns. In this study we compare unimanual with bimanual, tapping with oscillation, and self-paced with externally paced tasks, and we analyze the correlation properties of temporal patterns at both the component level and the coordinative level. Results show that the distinctive signatures of event-based versus emergent, and self-paced versus synchronization timing control known from unimanual tasks persist in the corresponding bimanual coordination tasks. Accordingly, we argue that these different timing processes, and related temporal patterns at the component level, constitute a task-dependent background on which coordination builds. One direct implication of these results is that the bimanual coordination paradigm should be considered multifaceted and not governed by some unitary generic principle. We discuss the need to assess the relationship between temporal patterns at the component level and the collective level, and to integrate serial (long-range) correlation properties into bimanual coordination models. Finally, we test whether the architectures of current bimanual coordination models can account for the experimentally observed serial correlations.     

Bimanual coordination dynamics in poststroke hemiparetics

Poststroke hemiparetic individuals (n = 9) and a control group (n = 9) completed a frequency-scaled circle-drawing task in unimanual and bimanual conditions. Measures of intralimb spatial and temporal task accuracy and interlimb coordination parameters were analyzed. Significant reductions in task performance were seen in both limbs of the patients and controls with the introduction of bimanual movement. Spatial performance parameters suggested that the 2 groups focused on different hands during bimanual conditions. In the controls, interlimb coordination variables indicated predictable hand dominance effects, whereas in the patient group, dominance was influenced by the side of impairment and prior handedness of the individual. Therefore, in this particular bimanual task, performance improvements in the hemiplegic side could not be elicited. Intrinsic coupling asymmetries between the hands can be altered by unilateral motor deficits.     

Timing goals in bimanual coordination

Phase coupling between movement trajectories has been proposed as the basic mechanism of hand coordination in the production of bimanual rhythmic movements with a 1:2 frequency ratio. Here a central temporal coupling view is proposed as an alternative. Extending previous models of two-handed synchronic and alternate-hand tapping, we hypothesized that 1:2 tapping is performed under the control of a single internal timekeeper set at the frequency required for the fast hand. The fast hand is assumed to use every signal and the slow hand every other signal of the timekeeper, to produce actions coordinated in time. The model's predictions for the variance-covariance pattern of tap timing within and across hands were tested in an experiment that required tapping with both hands with 1:1 or 1:2 frequency ratio. The finger contact on the response plate was to be short or long, according to instruction. Prolonged finger contact entailed profound modifications in the movement trajectories but failed to modify the variance-covariance pattern of the tap timing. This pattern proved to conform to predictions under both the short and the long contact conditions, thus supporting the central temporal coupling hypothesis.     

Hierarchical organisation of neuro-anatomical constraints in interlimb coordination

Based on the observation that bimanual finger tapping movements tend toward mirror symmetry with respect to the body midline, despite the synchronous activation of non-homologous muscles, F. Mechsner, D. Kerzel, G. Knoblich, and W. Prinz (2001) [Perceptual basis of bimanual coordination. Nature, 414, 69-73] suggested that the basis of rhythmic coordination is purely spatial/perceptual in nature, and independent of the neuro-anatomical constraints of the motor system. To investigate this issue further, we employed a four finger tapping task similar to that used by F. Mechsner and G. Knoblich (2004) [Do muscle matter in bimanual coordination? Journal of Experimental Psychology: Human Perception and Performance, 30, 490-503] in which six male participants were required to alternately tap combinations of adjacent pairs of index (I), middle (M) and ring (R) fingers of each hand in time with an auditory metronome. The metronome pace increased continuously from 1 Hz to 3 Hz over the course of a 30-s trial. Each participant performed three blocks of trials in which finger combination for each hand (IM or MR) and mode of coordination (mirror or parallel) were presented in random order. Within each block, the right hand was placed in one of three orientations; prone, neutral and supine. The order of blocks was counterbalanced across the six participants. The left hand maintained a prone position throughout the experiment. On the basis of discrete relative phase analyses between synchronised taps, the time at which the initial mode of coordination was lost was determined for each trial. When the right hand was prone, transitions occurred only from parallel symmetry to mirror symmetry, regardless of finger combination. In contrast, when the right hand was supine, transitions occurred only from mirror symmetry to parallel but no transitions were observed in the opposite direction. In the right hand neutral condition, mirror and parallel symmetry are insufficient to describe the modes of coordination since the hands are oriented orthogonally. When defined anatomically, however, the results in each of the three right hand orientations are consistent. That is, synchronisation of finger tapping is determined by a hierarchy of control of individual fingers based on their intrinsic neuro-mechanical properties rather than on the basis of their spatial orientation.     

Bimanual reaching across the hemispace: Which hand is yoked to which?

When both hands perform concurrent goal-directed reaches, they become yoked to one another. To investigate the direction of this coupling (i.e., which hand is yoked to which), the temporal dynamics of bimanual reaches were compared with equivalent-amplitude unimanual reaches. These reaches were to target pairs located on either the left or right sides of space; meaning that in the bimanual condition, one hand's contralateral (more difficult) reach accompanied by the other hand's ipsilateral (easier) reach. By comparing which hand's difficult reach was improved more by the presence of the other hand's easier ipsilateral reach, we were able to demonstrate asymmetries in the coupling. When the cost of bimanual reaching was controlled for the contralateral reaching left hand's performance was improved, suggesting that the left hand is yoked to the right during motor output. In contrast, the right hand showed the greatest improvements for contralateral reaching in terms of reaction time, pointing toward a dominant role for the left hand in the processes prior to movement onset. The results may point toward a mechanism for integrating the unitary system of attention with bimanual coordination.     

Temporal stability of rhythmic tapping “on” and “off the beat”: A developmental study

This study, following a dynamic pattern approach, examines age-related differences in the stability of unimanual rhythmic perception-action patterns. Thirty-six children, aged 7, 9, and 11 years, attempted to synchronize their finger tapping to the beats of an auditory metronome, either “on the beat” (i.e., in-phase coordination), or “off the beat” (i.e., antiphase coordination). The temporal stability of these perception- action patterns was measured by the variability of the relative phase between taps and auditory events and by the critical frequency, that is, the frequency at which a loss of stability was observed when the metronome frequency was increased. Age-related differences in stability were found for both relative phase variability and critical frequency. These findings suggest that the relative phase dynamics underlying perception-action coordination patterns change with age in the direction of an increased temporal stability. Received: 29 June 1998 / Accepted: 15 December 1998     

Crossing the arms confuses the clocks: Sensory feedback and the bimanual advantage

The bimanual advantage refers to the finding that tapping with two fingers on opposite hands exhibits reduced timing variability, as compared with tapping with only one finger. Two leading theories propose that the bimanual advantage results from the addition of either sensory (i.e., enhanced feedback) or cognitive (i.e., multiple timekeeper) processes involved in timing. Given that crossing the arms impairs perception of tactile stimuli and modulates cortical activation following tactile stimulation, we investigated the role of crossing the arms in the bimanual advantage. Participants tapped unimanually or bimanually with their arms crossed or uncrossed on a tabletop or in the air. With arms crossed, we expected increased interval timing variance. Similarly, for air tapping, we expected reduced bimanual advantage, due to reduced sensory feedback. A significant bimanual advantage was observed for the uncrossed, but not the crossed posture in tabletop tapping. Furthermore, removing tactile feedback from taps eliminated the bimanual advantage for both postures. Together, these findings suggest that crossing the arms likely impairs integration of internal (i.e., effector-specific) and external (i.e., environment-specific) information and that this multisensory integration is crucial to reducing timing variability during repetitive coordinated bimanual tasks.