Intermanual interactions during simultaneous execution and programming of finger movements

Handheld Computer Terminals: Starting off Right the First Time

Advances in miniaturization and wireless communications are providing the computer industry with the impetus to design handheld, portable computer terminals. Until enough research and experience evolves from handheld terminals to build a literature on design factors and to develop design guidelines and standards that would provide starting points for product design, the human factors community must rely on its user-centered design approach of designing, prototyping, and testing to ensure a safe and usable form factor for such terminals. The methodology that was used in establishing the design criteria for such a terminal included literature research, focus groups with potential users, contextual field research, expert testimony, and primary laboratory research, including a grasp analysis and screen viewability, data entry, signature capture, and holsterability testing. The user-centered design process described here provided the information required to establish the basic design criteria that would assure user safety and task efficiency. It also revealed informational needs for the human factors community involved in the development of handheld computer terminals.

Egocentric and allocentric constraints in the expression of patterns of interlimb coordination

Tasks that are easy when performed in isolation become difficult when performed simultaneously in the upper and/or lower limbs. This observation points to basic CNS constraints in the organization of patterns of interlimb coordination. The present studies provide evidence for the existence of two basic coordinative constraints whose effects may be additive under certain conditions. On one hand, the egocentric constraint denotes a general preference for moving the limbs toward or away from the longitudinal axis of the body in a symmetrical fashion and is of primary importance during the coordination of homologous limbs. On the other hand, the allocentric constraint refers to a general preference to move the limbs in the same direction in extrinsic space and pertains to the coordination of nonhomologous limbs (eg., various combinations of the upper and lower limbs). In the present context, constraints are considered as expressions of basic features of CNS operation that give way to preferred coordination patterns to which the system is naturally drawn or biased. The identification and description of these constraints is considered of critical importance to obtain a better understanding of the control of coordination patterns.

Temporal coupling is more robust than spatial coupling: an investigation of interlimb coordination after stroke

Interlimb coordination obtained through temporal and spatial coupling is a significant feature of human motor control. To understand the robustness of this capability the authors introduced a method to quantify interlimb coordination strength and compare individuals with asymmetric effector ability poststroke to nondisabled controls. Quantitative analyses determined the relative strength of interlimb coupling with an asymmetric obstacle avoidance task. Participants performed bimanual discrete, multijoint aiming movements in the frontal plane with a vertical barrier positioned midway to the target for one limb. To quantify coupling strength between limbs and groups, we regressed individual participant nonbarrier limb movement time or maximum vertical displacement separately, on barrier limb performance. Temporal and spatial interlimb coupling strength varied across participants in both groups. Barrier limb performance predicted nonbarrier limb behavior; however, interlimb coupling was significantly stronger for the nondisabled compared to the stroke group. In the stroke group, deficits in interlimb coordination affected spatial coupling more than temporal coupling. The decreased coupling strength detected, even in the presence of mild hemiparesis, demonstrates the measure's sensitivity. The authors propose this metric as a powerful assessment of the effectiveness of rehabilitation interventions and to monitor the recovery of bimanual coordination poststroke.

Dissociating the structural and metrical specifications of bimanual movement

Synchronization strength was investigated during the bimanual performance of movements with fundamentally different spatiotemporal features. A flexion (unidirectional) movement was made by the nondominant limb together with a flexion-extension-flexion (reversal) movement by the dominant limb. In contrast with previous studies on bimanual coordination, the movements differed from each other with respect to qualitative (structural) as well as quantitative (metrical) characteristics. Accordingly, the main task goal was to dissociate the limbs' actions at both these levels. Findings of Experiment 1 (within-subject) and Experiment 2 (between-subject) revealed a mutual synchronization effect that was evident at various levels of movement description and that was essentially asymmetric in nature: The unidirectional movement was more attracted to the reversal movement than vice versa. The intrusive nature of synchronization prevented full metrical and structural dissociation of the upper-limbs' actions, although individual differences were apparent and reflected fundamentally different coordination modes.

Do Muscles Matter for Coordinated Action?

This article investigates coordination stability when 2 fingers of each hand periodically tap together. The main question concerns the functional origin of the symmetry tendency, which has widely been conceived as a bias toward coactivation of homologous fingers and homologous muscular portions. In Experiment 1, the symmetry tendency was independent of finger combination. In Experiment 2, virtually identical stability characteristics were revealed under full vision and no vision. In Experiment 3, symmetrical and parallel visual labels on the fingers neither stabilized nor destabilized symmetrical and parallel tapping patterns. In Experiment 4, in which the relative position of the hands was varied, it revealed that the observed stability characteristics are to be defined in a hand-centered reference frame. Because the symmetry tendency was always independent of finger combination, the authors suggest that it is not a bias toward coactivation of homologous muscle portions but instead originates on a more abstract, functional level.

Rapid natural scene categorization in the near absence of attention

What can we see when we do not pay attention? It is well known that we can be "blind" even to major aspects of natural scenes when we attend elsewhere. The only tasks that do not need attention appear to be carried out in the early stages of the visual system. Contrary to this common belief, we report that subjects can rapidly detect animals or vehicles in briefly presented novel natural scenes while simultaneously performing another attentionally demanding task. By comparison, they are unable to discriminate large T's from L's, or bisected two-color disks from their mirror images under the same conditions. We conclude that some visual tasks associated with "high-level" cortical areas may proceed in the near absence of attention.

Development of bilateral motor control in children with developmental coordination disorders

This research examined behavioral (i.e. movement time) and neuromuscular (EMG) characteristics of unilateral and bilateral aiming movements of children with normal motor development and children with developmental coordination disorders (DCD). Two age groups of children were studied: 6 to 7, and 9 to 10 year olds. Bilateral aiming movements involved moving the two hands to targets of either (1) the same amplitude--symmetrical bilateral movements, or (2) different amplitudes--asymmetrical bilateral movements. Unilateral aiming movements involved moving one hand to either near or far targets associated with that hand. In general, unilateral and bilateral movement times were slower in younger than older children, and in children with DCD than children with normal motor development. Our neuromuscular data suggest that the faster movement times that typically accompany increasing age in children may be the result of a change in the capacity to initiate antagonist muscle contractions. The prolonged burst of agonist activity and delayed onset of antagonist activity observed in children with DCD may contribute to their inability to produce fast, accurate unilateral movements. On both symmetrical and asymmetrical bilateral aiming movements, children with DCD had more performance errors and greater temporal inconsistencies between neuromuscular (EMG) parameters and behavioral (movement time) parameters than children with normal motor development. These new neuromuscular data suggest that there are important differences in the way the motor control systems of children with and without DCD organize bilateral aiming responses.

Catching With Both Hands: An Evaluation of Neural Cross-Talk and Coordinative Structure Models of Bimanual Coordination

Kelso, Southard, and Goodman (1979) and Marteniuk and MacKenzie (1980) have each proposed a different theoretical model for bimanual coordination. In the model of Kelso et al., a close temporal relationship between the hands in a bimanual task is predicted, even when each hand is required to move different distances. In Marteniuk and MacKenzie's model, separate motor commands are issued so that each limb will arrive simultaneously at the specified movement endpoint, leading to low temporal associations between limbs. In most previous work on bimanual coordination, manual aiming tasks with differing constraints have been used by subjects in individual studies. In this study, the usefulness of existing models for predicting performance in a real-world catching task in which the required movement pattern was constrained by ball flight characteristics was examined. Eleven university students caught tennis balls with both hands in the following 3 conditions: Condition 1. Ball projected to the right shoulder area (left hand moved a greater distance than the right); Condition 2. Ball projected to center of the chest area, (both hands moved same distance); and Condition 3. Ball projected to left shoulder area (right hand moved a greater distance). Kinematic data (time to peak velocity, movement initiation time) indicating significant cross-correlations between the left and right limbs in all 3 conditions concurred with the data of Kelso et al. (1979) on manual aiming. Timing appeared to be an essential variable coordinating bimanual interceptive actions. Although the limbs moved at different speeds when each was required to move different distances, times to peak velocity showed strong associations, suggesting the presence of a coordinative structure.

What does the haptic modality do during cognitive activities on letter shapes? A study with left- and right-handers

This study was undertaken to analyze intermanual (interhemispheric) transfer in left and right handed subject and to assess how information was extracted during finger scanning of letter shape at the different levels of letter processing: shape recognition during a physical matching task, letter recognition in a verbal "meaning" matching task and letter naming. The dichhaptic procedure was used to study interhemispheric relations. It was hypothesized that cognitive activities have a feed-forward effect on the exploration of shapes, and that the performance is related to the nature of the task and to handedness. The exploratory strategies of the two types of handedness were also analyzed. The results showed that response latencies were generally similar for left- and right-handed subjects, but accuracy was better for left than right handers in "verbal" matching with the same overall exploratory strategies. In physical matching, left- and right-handed subjects performed equally but used different exploratory strategies. The naming task was very difficult for both groups but failed to discriminate their on accuracy, response latency, and exploratory strategy. The results are discussed with reference to the different exploratory strategies used and the interhemispheric interaction at work in different cognitive processes.

Age Factors Influencing Response–Response Compatibility in Reaction Time Tasks

Unlike stimulus–response compatibility, which has been explored for aging effects, the motor behavior issue of response–response (R–R) compatibility has not been addressed in the gerontological literature. R–R compatibility refers to the ease with which two responses can be prepared together either simultaneously or as choice alternatives. In the present study, young, middle-aged, and elderly adult female subjects were tested in a two-choice reaction-time (RT) paradigm involving four types of finger movements paired in every possible choice combination, creating different levels of R–R compatibility. Significant age differences increased as R–R compatibility decreased. The practical significance of this study is to establish R–R compatibility as an important factor influencing task difficulty to which older adults are particularly sensitive and to encourage recognition of this factor when prescribing progressive motor-skill training in elderly clients.

The bilateral reach to grasp movement

This study investigated the kinematic organization of bilateral reach to grasp movements. In Experiment 1 non-homologous bilateral movements were performed. One limb reached to grasp an object using whole hand prehension; the contralateral limb simultaneously reached to grasp an object using precision grip. Corresponding unilateral movements were assessed. Movement duration for each limb in the bilateral condition was similar. However, with earlier temporal settings for peak wrist acceleration and velocity, the limb performing precision grip showed a longer approach (deceleration) phase to the object. Unilateral precision grip movements showed a longer movement duration and deceleration phase than unilateral whole hand prehension movements. In Experiment 2 homologous bilateral movements were assessed. Both limbs performed either a reach and whole hand prehension or a reach and precision grip. Again the precision grip movements showed longer movement and deceleration times. Experiment 3 consisted of bilateral non-homologous pointing movements and a pointing movement with one limb while reaching to grasp with the contralateral limb. It was found that the earlier temporal settings of peak acceleration and velocity with the precision grip limb of the non-homologous bilateral task (Expt. 1) were largely due to the performance of distal grasping actions. It is concluded that a kinematic parameterization which is independent to each limb is evident for bilateral tasks which require functionally independent actions.

Structural constraints on bimanual movements

A theoretical framework is outlined, according to which structural constraints on bimanual movements can at least in part be understood as coupling between parameters of generalized motor programs. This framework provides a conceptual link between reaction-time data from experiments with bimanual responses, successive unimanual responses, and choice between left-hand and right-hand responses on the one hand and performance data obtained with concurrently performed continuous movements or sequences of discrete responses on the other. On the basis of data obtained with different methods for the study of intermanual interactions, a distinction is drawn between steady-state and transient constraints, and the hypothesis that the tendency to coactivate homologous muscles originates from a transient coupling of program parameters is applied to a variety of observations on performance in different tasks. Finally, the notion of transient constraints is applied to other types of intermanual interdependencies, and to interpersonal coordination; the possible emergence of transient constraints from steady-state constraints through progressive development of inhibitory pathways in childhood is discussed, as is the potential biological significance of transient constraints.

Spatial topological constraints in a bimanual task

Previous research has shown that the concurrent performance of two manual tasks results in a tight temporal coupling of the limbs. The intent of the present experiment was to investigate whether a similar coupling exists in the spatial domain. Subjects produced continuous drawing of circles and lines, one task at a time or bimanually, for a 20 s trial. In bimanual conditions in which subjects produced the circle task with one hand and the line task with the other, there was a clear tendency for the movement path of the circle task to become more line-like and the movement path of the line task to become more circle-like, i.e., a spatial magnet effect. A bimanual circle task and a bimanual line task did not exhibit changes in the movement path when compared to single-hand controls. In all bimanual conditions, the hands were tightly temporally locked. The evidence of temporal coupling and concomitant accommodation in the movement path for the conditions in which the hands were producing different shapes suggests that spatial constraints play a role in the governance of bimanual coordinated actions.

Relative phase destabilization during interlimb coordination: the disruptive role of kinesthetic afferences induced by passive movement

The disruption of three patterns of two-limb coordination, involving cyclical flexion-extension movements performed in the same or in different directions, was investigated through application of passive movement to a third limb by the experimenter. The three patterns referred to the homologous, homolateral, and heterolateral (diagonal) limb combinations which were performed in the sagittal plane. The passive movement involved a spatiotemporal trajectory that differed from the movements controlled actively. Even though subjects were instructed to completely ignore the passive limb movement, the findings of experiment 1 demonstrated a moderate to severe destabilization of the two-limb patterns, as revealed by analyses of power spectra, relative phase, cycle duration, and amplitude. This disruption was more pronounced in the homolateral and heterolateral than in the homologous effector combinations, suggesting stronger coupling between homologous than nonhomologous limb pairs. Moreover, passive mobilization affected antiphase (nonisodirectional) movements more than inphase (isodirectional) movements, pointing to the differential stability of these patterns. Experiment 2 focused on homolateral coordination and demonstrated that withdrawal of visual information did not alter the effects induced by passive movement. It was therefore hypothesized that the generation of extra kinesthetic afferences through passive limb motion was primarily responsible for the detriment in interlimb coordination, possibly conflicting with the sensory information accompanying active movement production. In addition, it was demonstrated that the active limbs were more affected by their homologous passive counterpart than by their nonhomologous counterpart, favoring the notion of "specific" interference. The findings are discussed in view of the potential role of kinesthetic afferences in human interlimb coordination, more specifically the preservance of relative phasing through a kinesthetic feedback loop.

The programming of structural properties of movement sequences

The present paper investigates the role of abstract structural properties in the programming and execution of movement sequences. Three experiments, using converging methods, demonstrate that the motor system represents the abstract structural properties of movement sequences. The first two experiments show that hierarchical structures over a sequence of tapping movements can be used to prepare the motor program, even if the specific elements of the sequence are still unknown. Experiment 2 also shows that the preliminary programming of structural properties of a movement sequence takes more time than the programming of specific elements (start elements). Experiment 3 suggests that abstract structural properties can be generalized from a special sequence and that they are transferable to other sequences. Abstract structural properties are assumed to be an important component of generalized motor programs.