Left-Handers and Right-Handers Compared on a Motor Task

Manual dexterity and keyboard use in spastic hemiparesis: a comparison between the impaired hand and the 'good' hand on a number of performance measures

OBJECTIVE

To assess the functional deficits in tapping performance of subjects with spastic hemiparesis.

DESIGN

In a pilot study, typing performance on a computer keyboard was examined on a number of performance measures.

SETTING

Department of Research and Development at the Werkenrode Institute.

SUBJECTS

Four subjects (mean age 16.4 years, standard deviation 1.8 years) with cerebral palsy and diagnosed as having spastic hemiparesis.

INTERVENTIONS

Subjects had to type a sequence of one or more keys as quickly as possible within an 8 second period with the fingers of both hands separately.

MAIN OUTCOME MEASURES

The average number of good and false responses were calculated. Within the false response category, four, mutually exclusive, types of errors were distinguished; wrong key, repetition, registrations under 75 ms and holding. Speed and regularity of the typing responses were also established.

RESULTS

The 'good' hand outperformed the impaired hand on all performance measures except on the amount of repetition errors made. The holding error was only present for the impaired hand, and there was an increase in holding errors from the index to the little finger in this hand. In addition, the impaired hand performed the task with a slower speed and in a more irregular fashion.

CONCLUSIONS

The results are discussed with reference to keyboard design. It is concluded that the standard 'QWERTY' keyboard hampers typing performance extensively, especially for subjects with left spastic hemiparesis. A learning method is presented in which the role of an external pacer (e.g. metronome) is discussed. This device can initially be used to decrease movement variability and, eventually, for increasing movement speed.

Stability of rhythmic finger movement in children with a developmental coordination disorder

The stability of single and bimanual (i.e., in-phase and antiphase) rhythmic finger movements was studied in 24 children with a developmental coordination disorder (DCD) and 24 matched controls from a dynamic pattern perspective. Stability was assessed by applying perturbations and measuring the time the system needed to return to its initial stability (i.e., the relaxation time). In addition, fluctuations of the patterns were measured. For antiphase coordination patterns, the frequency at which loss of stability occurred was also determined. Children with DCD displayed less stable single and bimanual rhythmic coordination patterns than control children. Further, within the DCD group, 9 children were identified as having particularly poor bimanual coordination stability. Individual differences suggested that variability of individual limb oscillations might have contributed to this poorer interlimb coordination stability. Findings were discussed in relation to a previous study on DCD in which the Wing-Kristofferson timekeeper model was applied.

Aspects of Psychomotor Performance in the Recovery from Right Hemisphere Lesions

The ability to learn and perform a psychomotor task (pursuit tracking task) of ten subjects who had sustained right hemisphere lesions (RHL) was compared to ten healthy individuals matched for age and gender. The task required subjects to react and move quickly, varying both the distance to be moved and the choice of movement direction. All subjects completed 1200 responses across two testing sessions. Results indicated that while the RHL group was able to ‘learn’ the task as well as the Control group, they were slower at correcting unanticipated movement errors. In addition, the RHL group did not respond to changes in the probable direction of the next movement in the same manner as the Control group and, in fact, appeared unaware of changes in the probability of movement direction.

Hand skill asymmetry in professional musicians

Hand skill asymmetry on two handedness tasks was examined in consistent right-handed musicians and nonmusicians as well as mixed-handed and consistent left-handed nonmusicians. Musicians, although demonstrating right-hand superiority, revealed a lesser degree of hand skill asymmetry than consistent right-handed nonmusicians. Increased left-hand skill in musicians accounted for their reduced asymmetry. Musicians predominantly playing keyboard instruments demonstrated superior tapping performance than musicians playing predominantly string instruments, although they did not differ with respect to hand skill asymmetry. Since the diminished tapping asymmetry in musicians was related to early commencement but not duration of musical training, results are interpreted as an adaptation process due to performance requirements interacting with cerebral maturation during childhood.

The Specificity of Motor Skill and Manual Asymmetry: A Review of the Evidence and Its Implications

Results of investigations on gaining control of limb movements are reviewed, and their contribution to understanding the development of manual asymmetries is discussed in relation to the discrimination and programming of appropriate neuromuscular resources. An examination of the relevant evidence on number and types of manual asymmetries recorded provides strong grounds for concluding that where asymmetries occur, they simply represent a further example of the well-documented activity-specific nature of motor skills and of the extremely lengthy periods of learning or experience needed for their acquisition and perfection. This specificity of motor skill and manual asymmetry also readily accounts for most of the discrepancy usually reported between assessments of hand preference and performance differences between hands, because these alternative measures of handedness have rarely employed the same range or variety of tasks.

Hand, space and attentional asymmetries in goal-directed manual aiming

Two experiments were conducted to explore the interaction of the two cerebral hemispheres in motor control, by examining hand, space and attentional asymmetries in goal-directed aiming. In Experiment 1, right-handed subjects moved to targets more quickly with their right hand than their left hand. In addition, each hand was faster when moving in its own hemispace. Although in a control condition, movements were initiated more quickly with the left hand, visual distractors disrupted left hand performance more than right hand performance. For contralateral aiming, ipsilateral distractors caused the greatest interference. In Experiment 2, when targets and distractors were all presented at the midline, a right hand advantage was found for movement time along with a left hand advantage for reaction time, independent of target and distractor location. Our findings are discussed in terms of a right hemisphere role in movement preparation and the allocation of attention in space, and greater left hemisphere involvement in movement execution.

Neuromuscular-skeletal constraints upon the dynamics of perception-action coupling

Four right-handed subjects performed rhythmic flexion and extension movements of the index finger in time with an auditory metronome. On each block of trials the forearm of the response hand was placed in a prone, neutral or supine position. In the flex-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger flexion with each beat of the metronome. In the extend-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger extension with each beat of the metronome. The frequency of the metronome was increased from 1.75 Hz to 3.50 Hz in eight steps (8-s plateaus) of 0.25 Hz. During trials prepared in the extend-on-the-beat pattern or to phase wandering often occurred, particularly at higher pacing frequencies. In marked constrast, during trials prepared in the flex-on-the-beat pattern such transitions were never present. Both the frequency and the alacrity of these transitions were greater when the forearm was in a prone or neutral position than when the forearm was in a supine position. These results are discussed with reference to the constraints imposed on the coordination dynamics by the intrinsic properties of the neuromuscular-skeletal system.

Functional psychomotor deficits associated with carpal tunnel syndrome

A reliable task was developed for investigating functional deficits associated with carpal tunnel syndrome (CTS). A rapid pinch and release psychomotor task utilizing muscles of the hand innervated by the median nerve was administered using a strain gauge dynamometer and providing limited force feedback. The motor performance characteristics studied were speed and force control. An experiment was conducted for studying the effects of force level, hand dominance, test-retest reliability, learning, and inter-subject variability using 13 subjects free from any hand disabilities or symptoms. A companion study was also conducted using 17 normal subjects and ten subjects diagnosed having CTS to investigate differences between CTS and control subjects. Dominant hands performed 4% to 8% better than the non-dominant hands by having a greater pinch rate, a smaller overshoot force, and less time above the upper force level and below the lower force level. Control subjects performed 25% to 82% better than CTS subjects. Age contributed 6% of the total variance for pinch rate and 7% of the total variance for the time below the lower force level. The results suggest that people suffering from CTS may experience similar functional psychomotor deficits in daily living and manual work activities.

Hand preference consistency and fine motor performance in young children

Recent investigations suggest that children who establish handedness early are better coordinated than those who lack this characteristic. To test this assumption, 160 4- to 6-year-olds were classified by consistent (established) and inconsistent (mixed) hand preference behavior and tested for fine motor performance using a finger tapping task. Analysis of the data revealed no significant differences existed between groups in finger tapping performance in relation to total sample, age or sex. Thus, contrary to recent reports, children with consistent and inconsistent hand preferences do not appear to differ in motor behavior as revealed by performance on a fine motor task. Furthermore, it appears that the performance of those with inconsistent hand preference presents a significant challenge to current theoretical notions of the genesis of handedness.

Hand performance of French children on a finger-tapping test in relation to handedness, sex, and age

Hand performance and laterality scores on a unimanual tapping test were studied in relation to age, sex, and handedness in a sample of 209 French children. Each child performed three trials with each hand. Older children were faster, but differences between hands were not related to age. Right-handed girls were more lateralized than right-handed boys. Left- and right-handers could be differentiated more clearly by tapping speed than by variability of tapping. A subsample of 36 right-handers were retested to estimate reliability. The coefficients were high, especially when using the mean of trials as the dependent variable. Correlations between performance on the tapping task and another test of hand-efficiency (dot-filling task) were low.

Is a dot-filling group test a good tool for assessing manual performance in children?

A dot-filling test was used to assess hand performance in two populations of French children. In the first experiment, the effect of sex, age and handedness on hand performance was examined (1742 children). Age was related to the degree of laterality, but girls were less lateralized than boys. The second experiment (200 children) showed that the surprising sex differences cannot be explained by the group testing procedure. Underlying processes leading to performance in the dot-filling task are probably different from those involved in other tests generally used for children.

Do "right-armed" lefthanders have different lateralization of motor control for the proximal and distal musculature?

Geschwind and Galaburda (1985) have suggested that specialization for the control of distal and proximal musculature might be located in different hemispheres in some individuals. Because inconsistent lefthanders (as defined by Ponton, 1987; Peters and Servos, 1989) tend to write with the left hand but throw with the right arm, and have a stronger right arm (Peters, 1990), it was thought that individuals in this group might provide evidence for the prediction made by Geschwind and Galaburda. This did not prove to be the case for tapping speed, where righthanders, inconsistent and consistent lefthanders all showed congruence. It appears that the question "are some left-handers right-armed?" can be answered only relative to specific activities.

The role of the hemispheres in closed loop movements

The purpose of these experiments was to determine if the two hemispheres play different roles in controlling closed loop movements. Subjects were asked to move to a narrow or wide target in the left or right hemispace. Reaction time (RT) was faster for the left arm of normals, only in the right hemispace, but there were no differences between arms in movement execution. Right but not left hemisphere stroke (CVA) patients showed longer RTs for the contralateral but not ipsilateral arm. The right CVA group's ipsilateral movement, especially to narrow targets was less accurate. The left CVA group's RT did not benefit from advanced information, but ipsilateral movement execution was normal. These results were discussed in terms of inter- as well as intrahemispheric control of programming and execution of closed loop movements.

Aimed movements to visual targets in hemiplegic and normal children: is the "good" hand of children with infantile hemiplegia also normal?

The accuracy, reaction and movement time of pointing movements to visual targets were examined in children aged 3-13 yr with infantile hemiplegia and compared to those of comparably aged normal children. Hemiplegic children pointed with the "good" hand (i.e. ipsilateral to the lesion). Half the normal children used the preferred hand, half the non-preferred hand. Movements were made with unrestricted/restricted visual feedback, when movement distance was short/medium/long, and when number of target alternatives were 2/4/8. Normal children using the preferred hand were more accurate but reacted more slowly than children using the non-preferred hand. The performance of most of the hemiplegic children with bilateral and/or unilateral lesions was impaired; degree of accuracy was related to the extent of the brain lesion; and reaction time was related to the level of intelligence. It was concluded that unilateral lesions in children can result in bilateral visuomotor impairment.

Hand preference, ability, and hemispheric specialization: in how far are these factors related in the monkey?

Reasons are given for preferring the term "hand-ability" to "hand-preference", especially in animals, for discussions of HS. Different kinds of HS are described for man and for the monkey, with emphasis on the importance of the precise task to be performed for the determination of HS ("act-specific HS"). Exceptional kinds of HS in the monkey are reported.

Hand Asymmetries in Interresponse Intervals During Rapid Repetitive Finger Tapping

Interresponse intervals (IRIs) were recorded as 8 right-handed male subjects tapped a key separately with the index finger of each hand as fast as possible for twenty 10-s runs. Frequency distributions of the IRIs produced by each hand showed that the shorter mean IRI that is usually reported for preferred-hand tapping is a result of a systematic production of shorter IRIs by the preferred hand. It is not secondary to inflation of the mean IRI of the non-preferred hand by the sporadic occurrence of long IRIs.

The dual task paradigm: speech dominance or manual dominance?

Two hundred and sixty monolinguals divided into subgroups based on gender, handedness, and familial left-handedness, were given a concurrent task, verbal-manual interference paradigm. The primary purpose of the study was to test whether the dual task interference effects were more related to hemispheric speech or manual dominance factors. The dominant hand, regardless of handedness, underwent relatively more tapping interference than the nondominant hand. The obtained results seriously question the basic assumptions underlying the interpretation of the dual task paradigm as an assessment index for hemispheric language lateralization. A possible explanation of this result that is in keeping with known hemispheric language representation proportions in left-handers is offered based on left hemisphere ipsilateral control of the left hand.

Differences between fingers and hands in tapping ability: dissociation between speed and regularity

The mean inter-tap interval (ITI) and the coefficient of variation of the ITI (ITIVAR) were measured in all five fingers of the preferred and non-preferred hand in two experiments. Subjects were right- or left-handed, males or females in experiments I and right-handed female typists, pianists, or controls in experiment II. Lack of consistent difference between right- and left-handers, and between those with and without special manual skills, suggested that hand differences in tapping are not a consequence of differential practise between hands. ITI showed differences both between fingers and between hands, whereas ITIVAR only showed differences between fingers. Separate mechanisms are inferred, and it is suggested that differences between fingers are a function of differential peripheral motor control, whereas differences between hands are a consequence of cerebral dominance of control mechanisms, and a model is presented.

Skill Level, Vision, and Proprioception in Simple One-Hand Catching

Two experiments examined the interaction of vision and articular proprioception in simple one-hand catching. In Experiment 1 (N = 18) skilled baseball and softball players used the left and right hands to catch slowly moving tennis balls, while Experiment 2 (N = 16) used novice catchers as subjects. In half the trials, sight of the catching hand was prevented by placing a screen alongside the subjects' face. Results of Experiment 1 revealed that the screen caused minimal disruption of the positioning phase of the catch, with moderate disruption of the grasping phase. However, for the unskilled subjects of Experiment 2, the screen caused considerable disruption of positioning. The data provide only minimal support for Smyth and Marriott' (1982) contention that limb position is inadequately specified by articular proprioception. It is argued that skill level serves as a mediator in the ability to use proprioception for limb positioning, but vision appears necessary to control the precise temporal organization of the grasp phase of one-hand catching.

Comparing different measures of laterality: do they relate to a single mechanism?

In the present study, a total of 126 adults were given three dichotic tasks, two half-field tasks, a peg-board task, several tapping tasks, the dynamometer, and a handedness questionnaire. A hierarchical cluster analysis was carried out on the matrix of product-moment correlations of laterality scores for all possible pairs of tasks. This analysis suggested that the laterality scores fall into three clusters: auditory (dichotic listening) scores, visual (half-field) scores, and manual (performance) scores. Canonical correlation analysis showed that these clusters must be considered to be independent of each other. The results are discussed with respect to the traditional interpretation of the concept of laterality. It is suggested that laterality phenomena may be dissociated and that this possibility deserves more attention.

Lateral asymmetries in arm, wrist and finger movements

On the assumption of contralateral control, lateral asymmetries in motor performance are often associated with the functional specialization of the cerebral hemispheres. However, anatomical as well as previous behavioral studies, indicate this assumption may not be valid for all joints of the limbs. To test this assumption, right-handed male subjects performed a rapid tapping task using movements of the index finger, the wrist, or the shoulder. The hand used and order of conditions were counterbalanced across subjects. The rate and variability data were submitted to a 2 x 3 (hand x joint) Analysis of Variance with repeated measures on both factors. For both rate and variability significant (all p less than .01) main effects were evident for hand and joint with no significant interactions. It is argued that the variability of tapping reflects the processing mode of the contralateral hemisphere and thus leads to the conclusion that crossed pathways are the principal mechanism for controlling rapid movements of all limb joints. It is tentatively concluded that where either crossed or ipsilateral pathways are available, the type of movement control required will dictate which pathway is used.

Hand Differences in the Rate and Variability of Rapid Tapping

Hand differences in the rate and variability of rapid tapping were evaluated for the intertap interval and its constituents-the key depression and key release phases of each tap. To accentuate potential hand differences, only subjects with a clear manual superiority in one hand were included. Relative manual proficiency on Fitts' reciprocal tapping task was used to exclude individuals with less-defined hand superiority or dominance, and to categorize subjects as having a dominant left (n=13) or right (n=11) hand. Analysis of variance indicated the dominant hand to have a shorter average intertap interval and thus a faster tapping rate. This hand difference in rate was found to be significant for the key-depression phase, but not the key-release.phase, of the tap. In each handedness group the dominant hand exhibited less variability in the intertap interval and both constituents. Potential associations of these findings with hemispheric asymmetries in sequential ability are discussed.