Intermanual interactions related to movement amplitudes and endpoint locations

In almost all studies of bimanual movements with same and different amplitudes, the difference between amplitudes has been confounded with a difference between endpoint locations. The present authors varied those parameters orthogonally. In addition, they presented target locations on the surface on which the movements were produced (direct cues) and on a monitor (indirect cues). Participants' (N = 12) reaction times were longer when both amplitudes and endpoint locations differed than when they were the same. Intermanual amplitude correlations were reduced whenever 1 of the movement parameters differed for the 2 hands; only when cues were presented on the monitor was the amplitude correlation further reduced when both movement parameters were different. The results indicate that structural constraints on bimanual movements take effect on both amplitudes and endpoint locations. The relative importance of those 2 parameters is largely independent of the type of cue.     

Bimanual interference associated with the selection of target locations

Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand.     

Specification of movement amplitudes for the left and right hands: evidence for transient parametric coupling from overlapping-task performance

Bimanual coordination tasks suggest transient cross-talk between concurrent specification processes for movements of the left and right hand that vanishes as the time for specification increases. In 2 experiments with overlapping and successive unimanual tasks, the hypothesis of transient coupling was examined for a psychological-refractory-period paradigm. Time for specification was manipulated by varying the delay between first and second signal (Experiment 1) and by precuing the first response (Experiment 2). Participants performed rapid reversal movements of same or different amplitudes with the left and right hands. With different amplitudes, reaction times (RTs) of the second responses were longer than with same amplitudes at short delays, and this disappeared at longer delays in Experiment 1. In Experiment 2, precuing also reduced the difference between RTs of second responses in same-amplitude and different-amplitude trials. These findings are consistent with the hypothesis of transient coupling during amplitude specification obtained with bimanual tasks.     

Cognitive constraints on motor imagery

Executed bimanual movements are prepared slower when moving to symbolically different than when moving to symbolically same targets and when targets are mapped to target locations in a left/right fashion than when they are mapped in an inner/outer fashion [Weigelt et al. (Psychol Res 71:238–447, 2007)]. We investigated whether these cognitive bimanual coordination constraints are observable in motor imagery. Participants performed fast bimanual reaching movements from start to target buttons. Symbolic target similarity and mapping were manipulated. Participants performed four action conditions: one execution and three imagination conditions. In the latter they indicated starting, ending, or starting and ending of the movement. We measured movement preparation (RT), movement execution (MT) and the combined duration of movement preparation and execution (RTMT). In all action conditions RTs and MTs were longer in movements towards different targets than in movements towards same targets. Further, RTMTs were longer when targets were mapped to target locations in a left/right fashion than when they were mapped in an inner/outer fashion, again in all action conditions. RTMTs in imagination and execution were similar, apart from the imagination condition in which participants indicated the start and the end of the movement. Here MTs, but not RTs, were longer than in the execution condition. In conclusion, cognitive coordination constraints are present in the motor imagery of fast (<1600 ms) bimanual movements. Further, alternations between inhibition and execution may prolong the duration of motor imagery.     

Intermanual cross-talk effects in unimanual choice reactions

Intermanual interactions originate at different levels of motor control. Interactions during specification of movement characteristics should affect reaction time for choice between left-hand and right-hand movements. In two experiments combinations of short and long target amplitudes for reversal movements of the left and right hand were cued with variable precueing intervals. Upon presentation of the response signal a unimanual left-hand or right-hand movement had to be produced. Reaction time was faster when same target amplitudes were precued than when different target amplitudes were. At short precueing intervals the longer reaction time with different target amplitudes (early effect) was accompanied by an amplitude assimilation: Short amplitudes were too long, and long amplitudes were too short. At longer precueing intervals the longer reaction time with different target amplitudes (late effect) was accompanied by a higher choice accuracy. These findings are taken to indicate a transient parametric coupling of amplitude specifications, which produces the early and the late effects by way of different mechanisms-namely different degrees of advance specification and generalized de-coupling, which affects the process of choice between hands.     

The influence of movement cues on intermanual interactions

In two experiments, we studied intermanual interactions in bimanual reversal movements and bimanual aiming movements. Targets were presented on a monitor or directly on the table on which the movements were produced. Amplitudes for each hand were cued symbolically or spatially either in advance of an imperative signal or simultaneous with it. In contrast to findings of Diedrichsen et al. (Psychological Science, 12, 493–498, 2001), reaction times for different-amplitude movements were longer than for same-amplitude movements both for symbolic and spatial cues presented on the monitor and directly on the table. However, with symbolic cues the effect of the relation between target amplitudes was considerably stronger than with spatial cues, no matter where the cues were presented. Intermanual correlations of amplitudes, movement times, and reaction times were smaller with different than with same target amplitudes, and this modulation was more pronounced when targets and cues were presented on the monitor than when they were presented on the table. The findings are taken to suggest that the basic reaction-time disadvantage of different-amplitude movements results from interference between concurrent processes of amplitude specification. Additional factors like interference between concurrent processes of mapping cues on movement characteristics may add strongly to it.     

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni-versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 8 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as the anticipate mirror manipulations of the object less. The frequency of bimanual reaches increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.     

Target-related coupling in bimanual reaching movements

While bimanual interference effects can be observed when symbolic cues indicate the parameter values of simultaneous reaching movements, these effects disappear under conditions in which the target locations of two movements are cued directly. The present study investigates the generalizability of these target-location cuing benefits to conditions in which symbolic cues are used to indicate target locations (i.e., the end points of bimanual movements). Participants were asked to move to two of four possible target locations, being located either at the same and different distances (Experiment 1), or in the same and different directions (Experiment 2). Circles and crosses served as symbolic target-location cues and were arranged in a symmetric or non-symmetric fashion over the four target locations. Each trial was preceded by a variable precuing interval. Results revealed faster initiation times for equivalent as compared to non-equivalent target locations (same vs. different cues). Moreover, the time course of prepartion suggests that this effect is in fact due to target-equivalence and not to cue-similarity. Bimanual interference relative to movement parameter values was not observed. These findings suggest that cuing target locations can dominate potential intermanual interference effects during the concurrent programming of different movement parameter values.     

The control of amplitude and direction in a bimanual coordination task

Bimanual coordination requires task-specific control of the spatial and temporal characteristics of the movements of both hands. The present study focused on the spatial relationship between hand movements when their amplitude and direction were manipulated. In the experiment in question, participants were instructed to draw two lines simultaneously. These two lines were instructed to be drawn in mirror symmetric or perpendicular directions of each other while the length was instructed to be the same or different. The coordinative quality of amplitude control was compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Results showed that the amplitude accuracy decreased when different amplitudes and/or directions had to be generated simultaneously. The coordinative quality of direction was also compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Unlike amplitude, the direction accuracy was largely independent of coordination symmetry/asymmetry of direction or amplitude. The results suggest that the coordinative quality of amplitude control does not only interfere with amplitude asymmetry, but it also interferes with direction asymmetry. Moreover, in bimanual coordination amplitude control is more vulnerable to the influence of direction control demands than vice versa.     

Structural Constraints on the Performance of Symmetrical Bimanual Movements with Different Amplitudes

In bimanual movements the amplitude of each hand's movement often depends on the concurrent amplitude of the other hand's movement such that both amplitudes become similar (amplitude coupling). We tested the hypothesis that the strength of amplitude coupling depends on the tempo of performance of a movement sequence, a hypothesis based on a model of bimanual coordination that holds that cross-talk occurs at the execution level as well as at the programming level. Subjects performed bimanual periodic arm movements on two digitizers. In nine conditions constant small, constant large, and alternating small and large amplitudes of each arm were orthogonally combined. Overall tempo was varied by instructing subjects to increase the tempo progressively by 10%. Clear tempo-dependent modulations of the amplitude were observed in movements with instructed constant amplitude when the other hand performed alternating amplitudes. The effect of the size of constant-amplitude movements on the mean amplitude of the other hand indicated cross-talk at the execution level. Cross-talk at the programming level was revealed by the dependence of the current amplitude on the change in the amplitude of the other hand in the preceding cycle. Finally, asymmetric cross-manual effects were observed.     

Moving to Directly Cued Locations Abolishes Spatial Interference During Bimanual Actions

Interference is frequently observed during bimanual movements if the two hands perform nonsymmetric actions. We examined the source of bimanual interference in two experiments in which we compared conditions involving symmetric movements with conditions in which the movements were of different amplitudes or different directions. The target movements were cued either symbolically by letters or directly by the onset of the target locations. With symbolic cues, reaction times were longer when the movements of the two hands were not symmetric. With direct cues, reaction times were the same for symmetric and nonsymmetric movements. These results indicate that directly cued actions can be programmed in parallel for the two hands. Our results challenge the hypothesis that the cost to initiate nonsymmetric movements is due to spatial interference in a motor-programming stage. Rather, the cost appears to be caused by stimulus identification, response-selection processes connected to the processing of symbolic cues, or both.     

Bimanual interference with compatible and incompatible tool transformations

The present study investigates bimanual interference in a tool-use task, in which two target locations had to be touched concurrently with two tools, one for each hand. Target locations were either in the same, or in different directions for the two hands. Furthermore, the tools implemented either a compatible or an incompatible relationship between the direction of target locations and the direction of associated bodily movements. Results indicated bimanual interference when the tools had to be moved to targets in different directions. Furthermore, this interference was much more pronounced when the tools required body movements that were spatially incompatible to the cued target locations as compared to when they were compatible. These results show that incompatible relationships between target directions and bodily movement directions can aggravate bimanual interference in tool use.     

Brief bimanual force pulses: correlations between the hands in force and time.

Three experiments assessed coupling phenomena in the coordination of bimanual force pulses. Experiment 1 required symmetric force pulses (equal target forces and rise times for both hands) using the index finger of each hand. As the authors expected, on the basis of bimanual pointing movement results, this experiment revealed positive correlations between both the force rise times and the force amplitudes of the two hands. Experiments 2 and 3 included asymmetric conditions with different target force amplitudes (Experiment 2) or target rise times (Experiment 3). In Experiment 2 force amplitudes but not rise times were fully decoupled in the asymmetric condition. In the asymmetric condition of Experiment 3, however, neither rise times nor force amplitudes were fully decoupled. The results suggest a hierarchical control structure with temporal control dominating nontemporal control of bimanual force coordination.     

Coordinated flexibility: how initial gaze position modulates eye-hand coordination and reaching

Reaching to targets in space requires the coordination of eye and hand movements. In two experiments, we recorded eye and hand kinematics to examine the role of gaze position at target onset on eye-hand coordination and reaching performance. Experiment 1 showed that with eyes and hand aligned on the same peripheral start location, time lags between eye and hand onsets were small and initiation times were substantially correlated, suggesting simultaneous control and tight eye-hand coupling. With eyes and hand departing from different start locations (gaze aligned with the center of the range of possible target positions), time lags between eye and hand onsets were large and initiation times were largely uncorrelated, suggesting independent control and decoupling of eye and hand movements. Furthermore, initial gaze position strongly mediated manual reaching performance indexed by increments in movement time as a function of target distance. Experiment 2 confirmed the impact of target foveation in modulating the effect of target distance on movement time. Our findings reveal the operation of an overarching, flexible neural control system that tunes the operation and cooperation of saccadic and manual control systems depending on where the eyes look at target onset.     

Bimanual cross-talk during reaching movements is primarily related to response selection,not the specification of motor parameters

Simultaneous reaching movements made with the two hands can show a considerable increase in reaction time (RT) when they differ in terms of direction or extent, compared to when the movements involve the same direction and extent. This cost has been attributed to cross-talk in the specification of the motor parameters for the two hands. However, a recent study [Diedrichsen, Hazeltine, Kennerley, & Ivry, (2001). Psychological Science, 12, 493-498] indicates that when reaching movements are cued by the onset of the target endpoint, no compatibility effects are observed. To determine why directly cued movements are immune from interference, we varied the stimulus onset asynchrony for the two movements and used different combinations of directly cued and symbolically cued movements. In two experiments, compatibility effects were only observed when both movements were symbolically cued. No difference was found between compatible and incompatible movements when both movements were directly cued or when one was directly cued and the other was symbolically cued. These results indicate that interference is not related to the specification of movement parameters but instead emerges from processes associated with response selection. Moreover, the data suggest that cross-talk, when present, primarily shortens the RT of the second movement on compatible trials rather than lengthening this RT on incompatible trials.     

Target selection during bimanual reaching to direct cues is unaffected by the perceptual similarity of the targets

Investigations of bimanual movements have shed considerable insight on the constraints underlying our ability to perform coordinated actions. One prominent limitation is evident when people are required to produce reaching movements in which the two trajectories are of different amplitudes and/or directions. This effect, however, is only obtained when the movements are cued symbolically (e.g., letters indicate target locations); these planning costs are absent when the target locations are directly cued (J. Diedrichsen, E. Hazeltine, S. Kennerley, & R. B. Ivry, 2001). The present experiments test whether the absence of planning costs under the latter condition is due to the perceptual similarity of the direct cues. The results demonstrate that measures of response planning and execution do not depend on the perceptual similarity of the direct cues. Limitations in our ability to perform distinct actions with the two hands appear to reflect interactions related to response selection involving the translation of symbolic cues into their associated movements rather than arise from interactions associated with perception, motor programming, and motor execution.     

Does hand dominance affect the use of motor abundance when reaching to uncertain targets?

This study investigated hemispheric differences in utilizing motor abundance to achieve flexible patterns of joint coordination when reaching to uncertain target locations. Right-handed participants reached with each arm to the same central target when its final location was certain or when there was a 66% probability that its location could change after movement initiation. Use of greater motor abundance was observed when participants reached to the central target under target location uncertainty regardless of the arm used to reach. Joint variance associated with variability of movement direction was larger when reaching with the left, non-dominant arm. This arm also exhibited higher hand path variability compared to the dominant arm. These arm differences were not found when the final (central) target location was known in advance. The results provide preliminary evidence for a greater ability of the dominant (right) arm/left hemisphere to decouple directions in joint space. That is, to increase the use of motor abundance without simultaneously inducing unwanted hand path variability requires that joint variations be restricted to a limited subspace of joint space. Hemispheric differences in motor planning did not appear to account for arm differences related to the use of motor abundance.     

Intermanual interactions during programming of aimed movements: Converging evidence on common and specific parameters of control

Summary Reaction time for choice between left-hand and right-hand responses sometimes depends on whether the responses assigned to the two hands are the same or different, but sometimes it does not. It has been suggested that the result obtained indicates whether the variable on which the responses differ is determined by common or specific parameters of control. Common parameters apply to movements of both hands, but specific parameters can be set independently for left-hand and right-hand responses. The interpretation of choice RT in terms of intermanual interactions requires that the conclusions converge with conclusions that are based on studies of simultaneous movements, provided that interactions can indeed be attributed to common parameters. Results from the latter type of experiment suggest that duration of aimed movements is determined by common parameters, but amplitude is determined by specific parameters. In two experiments it is shown that the choice-task results are consistent with this conclusion: Choice RT increases when the choice is between aimed movements that differ in duration, but not if the choice is between movements of different amplitudes. Further, an assimilation of responses is found in the former case but not in the latter. These findings are taken as further support for the notion of intermanual interactions during motor programming.     

Spatial Error Detection and Assimilation Effects in Rapid Single and Bimanual Aiming Movements

In 2 experiments, spatial error detection capability and movement accuracy were investigated in both single and bimanual rapid aiming movements. In both experiments, right-handed college-age participants (N = 40 [Experiment 1]; N = 24 [Experiment 2]) used light, aluminum levers to make quick single and dual reversal movements in the sagittal plane in a time to reversal of 210 ms to either the same or different target locations involving identical (Experiment 1) or mirror-image (Experiment 2) movements. In Experiment 1, the shorter-distance limb overshot the target by 15-23&percent; when paired with a limb traveling at least 20 degrees farther, but no spatial assimilations were shown when movements differed by 20 degrees or less. In Experiment 2, the shorter-distance limb overshot 22-29&percent; when paired with a limb traveling 20 degrees farther, but spatial assimilations were not mitigated when both limbs moved to the same target position. Participants underestimated movement amplitude in all dual conditions but particularly when spatial assimilations were noted. Correlations between actual and estimated errors decreased from single to dual trials in both experiments. The findings suggest that spatial assimilations are caused by bimanual differences in movement amplitude, regardless of movement direction, and that individuals have greater difficulty identifying errors in simultaneous actions, especially when spatial assimilations are present, than identifying errors in single-limb actions.     

Bimanual coordination in chronic schizophrenia

Anomalies of movement are observed both clinically and experimentally in schizophrenia. While the basal ganglia have been implicated in its pathogenesis, the nature of such involvement is equivocal. The basal ganglia may be involved in bimanual coordination through their input to the supplementary motor area (SMA). While a neglected area of study in schizophrenia, a bimanual movement task may provide a means of assessing the functional integrity of the motor circuit. Twelve patients with chronic schizophrenia and 12 matched control participants performed a bimanual movement task on a set of vertically mounted cranks at different speeds (1 and 2 Hz) and phase relationships. Participants performed in-phase movements (hands separated by 0 degrees ) and out-of-phase movements (hands separated by 180 degrees ) at both speeds with an external cue on or off. All participants performed the in-phase movements well, irrespective of speed or cueing conditions. Patients with schizophrenia were unable to perform the out-of-phase movements, particularly at the faster speed, reverting instead to the in-phase movement. There was no effect of external cueing on any of the movement conditions. These results suggest a specific problem of bimanual coordination indicative of SMA dysfunction per se and/or faulty callosal integration. A disturbance in the ability to switch attention during the out-of-phase task may also be involved.