Finger tapping: effects of trials and sessions

18 normal, self-reported dextral subjects (9 men, 9 women) were assessed with a Halstead Manual Finger Tapping device, with 10 trials per hand for 10 consecutive wk. The test-retest reliability of the 10-trial average between the 10 sessions averaged .94 for men and .86 for women, for both preferred and nonpreferred hands. There were no statistically significant effects of increases in performance over sessions or effects of fatigue over trials for either sex or hand. There were, however, significant increases over trials for men for both preferred and nonpreferred hands.     

Performance Asymmetries in Computer Mouse Control of Right-Handers, and Left-Handers with Left- and Right-Handed Mouse Experience

Precision and general computer mouse aiming performance by right-handers (RH-RM) and left-handers with right-handed mouse experience (LH-RM) and by left-handers with left-handed mouse experience (LH-LM) were compared. A number of performance measures, such as reaction time, time to reach a target, time to click on target, and cursor trajectory, were analyzed. Superficially, specific hand experience seemed to dictate performance asymmetries, but a closer look revealed interactions between hand preference and hand performance. That finding has implications for theories of handedness. In addition, precision and general directional aiming with the mouse cursor showed a clear right hand superiority in reaction time in both RH-RM and LH-RM subjects, whereas LH-LM subjects showed no lateral asymmetries. Finally, the overall time taken for the task, averaged across groups and conditions, favored the experienced hand by some 180 ms. In practical terms, that is not a large difference, especially because the difference will be reduced with practice. Thus, the use of the inexperienced hand can be advocated when there is a need to forestall or ameliorate repetitive stress in the experienced hand.     

The Measurement of Handedness by Preference and Performance Tests

Hand preference and hand proficiency were compared on 50 male subjects (30 self-classified left-handers and 20 self-classified right-handers) according to their responses to a 20 item questionnaire and their performances on a handwriting and a grip-strength task. Performance differences between the two sides for each group were not related to overall preference assessments but were positively associated with hand preferences on corresponding questionnaire items. Distributions of the performance differences between the two sides for the right- and left-handers were well separated for handwriting but completely overlapped for grip strength. Significant correlations between the performances on each side were recorded on both tasks. The results stress the importance of using the same criteria in making preference vs. performance comparisons and highlight the need to recognize and control the influence of previous training or experience.     

Lateralization of bilateral transfer of visuomotor information in right-handers and left-handers

The author examined the lateralization of transfer of visuomotor information between the right and left hands during unimanual finger-tapping sequences with visual feedback. The finger-tapping task consisted of a target peak force of 2 N and a target intertap interval of 500 ms. Twenty right-handed and 10 left-handed participants performed the motor task, with 3 transfer trials following 3 practice trials. The author observed positive transfers from the left to the right hand for right-handers but the opposite direction of positive transfers for left-handers. However, left-handers showed a less variable peak force than right-handers did. The author discusses left-handers' interhemispheric information processing.     

Constraints in the performance of bimanual tasks and their expression in unskilled and skilled subjects

Unskilled and skilled subjects were asked to perform a variety of bimanual tapping tasks. Three major effects were seen. First, right-handers performed dual tasks better when the preferred hand took the “figure” and when the nonpreferred hand took the “ground” of the dual movement. This effect was not seen in left-handers. Second, subjects performed a simple slow/fast dual task better when they commenced the task with the fast rather than with the slow hand. This effect was seen in right- and lefthanders. Third, both unskilled and skilled subjects showed marked interdependence of movements such that performance of one hand was a function of movements in the other hand. The results are in agreement with a model that postulates the presence of a superordinate control mechanism that initiates action in subordinate control mechanisms, which in turn set the movement trajectories in the two hands. The results also show that attention is an important factor in the interaction between these two levels of control.     

Attentional distribution of task paramters to the two hands during bimanual performance of right- and left-handers

The author tested 12 left-handers and 12 right-handers on a bimanual circling task to examine how attention (either visual or nonvisual) to the task of 1 hand affects within-hand task parameters and whether the effects of attention manipulations are similar in left- and right-handers. The novel prediction that the attended task would be produced larger than the unattended task was confirmed in both handedness groups. The magnitude of the effect on circle size was more pronounced under visual than under nonvisual attention manipulations. The primary effects of attention were similar in the 2 handedness groups, although left-handers demonstrated some evidence of stronger parameter coupling between hands than right-handers did.     

A review, analysis, and some new data on hand-posture distributions in left-handers

Different methods have been employed to assess handwriting posture in left-handers, and different dimensions of hand posture have been used for categorization. Within North American samples, there is a remarkable consistency between studies in the distributions when the same assessment method is used, but there are very large and highly significant differences for different methods of assessment. The various methods and dimensions of categorization evidently index different variables, and these are likely to have different relations with neuropsychological factors. It is possible, however, to gather questionnaire data on handwriting posture that closely resemble direct experimenter observation, as a brief report on left-handed males shows.     

Sex Differences in Perception: Exploring the Integration of Sensory Information with Respect to Vision and Proprioception

Inter- and intra-modal matching by right hand preferred Norwegian adults were tested using a matching task. The task required them to locate target pins visually, proprioceptively or in combination, while matching was always carried out without vision. When combined scores for both hands were analysed, the females showed superior performance in the intra-modal matching condition. For both groups, when the scores for the two hands were treated separately, superior performance was obtained in using the right hand to match under the visual condition. The only significant sex difference relative to hand preference was that the females matched the target more accurately with the right hand in the intra-modal matching condition. These findings are discussed relative to inter-hemispheric processing     

Asymmetrical transfer of training between hands: implications for interhemispheric communication in normal brain

Two experiments are presented which investigated claims of asymmetrical transfer of training between the hands/hemispheres. In Experiment 1, 96 right- and left-handed male undergraduates practiced an inverted-reversed printing task with either the right or the left hand. Transfer to the opposite hand was then compared to same-hand transfer, in a between-subject design. In Experiment 2, 176 right-handed boys and girls were tested at ages 7, 9, and 11 years. For right-handed subjects in both experiments, the left hand benefited more from opposite-hand training than did the right. The reverse was true for left-handers in Experiment 1, although one group (who wrote with the "inverted" position) showed little transfer in either direction. Two current models of interhemispheric interaction do not satisfactorily explain these findings. A third model, based on cross-activation, may provide a more effective alternative.     

Hand dominance, attention, and the choice between responses

Thirty pairs of matched right- and left-handed subjects carried out a serial C.RT task involving reaches between 2.4 cm square contact grids set at 2.4 cm intervals in a horizontal line. In one condition they responded with the right hand alone, in a second with the left and in a third they had to choose between hands on each trial responding to left side grids with the left hand and to right side grids with the right.

All subjects took longer to respond when they had to choose between hands than when they used either hand alone. In the one-hand conditions neither group showed any effect of hand dominance. When choices had to be made between hands both groups responded faster with their dominant than with their nondominant hands.

Analysis of the results was undertaken in terms of two hypothetical systems of instructions which might control machines designed to carry out similar tasks. It is concluded that in some tasks hand dominance can be described in terms of an attentional bias towards the field of operation of one effector rather than another. In the present task the effects of such possible attentional biases were shown not to interact with other effects, such as the facilitation of successive responses by repeated use of the same limb. These latter effects seem to depend on processes underlying execution of responses rather than choices between responding limbs.     

Left-handers and right-handers compared on a motor task

Finger-tapping performance of 45 subjects of each sex and handedness combination, for a total of 180, was compared. Performance measures were speed (mean intertap interval) and regularity (standard deviation of intertap interval). Males tapped faster but not more regularly than females. The between-hand differences in performance were smaller for both measures in left-handers. When absolute magnitudes of between hand differences were compared, females showed smaller differences in regularity of tapping than males. Speed and regularity of tapping were statistically independent; both measures discriminated well between the preferred and nonpreferred hand of both handedness groups, but the differences in speed were more marked than the differences in regularity. Data on the performance of children on the same task are included for comparative purposes.     

Asymmetrical transfer of braille acquisition between hands

Two experiments are presented which demonstrate asymmetrical transfer for tactual recognition of individual braille letters in sighted subjects, a task usually associated with right hemisphere specialization. Right-handers were studied in Experiment 1, left- and right-handers in Experiment 2. Poor transfer of training from the right hand to the left hand was observed for right-handed subjects in both experiments. The same was true for one group of left-handers (who wrote with the "inverted" position). For another group (who wrote with the "noninverted" position), no disadvantage was associated with opposite-hand training for either hand. The role of hemispheric specialization of function in determining the direction of greater transfer is discussed, and it is argued that handwriting posture may be an index of the degree of functional "connectedness" of the two hemispheres in left-handers.     

Intrahemispheric response competition between vocal and unimanual performances in normam adult human males.

Subjects balanced a dowel rod vertically on the left and right index finger singly and while simultaneously repeating phrases. With right-handed subjects who had no left-handed relatives, concurrent verbalization shortened right- but not left-handed balancing. Increased phonetic difficulty of the phrases produced an increased decrement on right-handed balancing, but left-handed balancing was unchanged; it also produced more verbalization errors on trials with the right hand, but not with the left. Concurrent verbalization shortened balancing duration with both hands of left-handers. Right-handers with left-handed relatives produced variable results. Concurrent humming also selectively interfered with right-handed balancing. It was concluded that the results conform to an interpretation based on intrahemispheric interference between incompatible, simultaneously produced sets of responses.     

The influence of handedness on profile and line drawing directionality in children,young, and older normal adults

One hundred twenty-two normal subjects--children, young and older adults (77 right-handers and 45 left-handers)--performed two drawing tasks in order to study their directionality trends. The first task consisted of drawing the profile of a face and in the second task subjects had to link two points in order to draw a line. The analysis of the drawing directionality revealed a significant effect of the age when right-handers drew profiles whereas this effect reached significance in left-handed subjects only when drawing lines. Left- and right-handers' performances across the two tasks were found to significantly differ. Results are discussed in terms of hemispheric and environmental factors.     

Laterality and directional preferences in a simple perceptual-motor task

The superiority of tensor or outward movements of hand and arm over flexor or inward movements has been described, but no evidence has been found relating to directional preferences in simple perceptual-motor tasks.

One hundred children, aged 9 to 13, 50 being right-handed writers and 50 left-handed writers, were tested on a stroke-making task, using both preferred and non-preferred hands. 75 per cent, of them exhibited a preference for outward movements of both hands, a finding which applied equally to both handedness groups. Thus an explanation based on writing habits is discounted.     

Mirror-reading in right- and left-handers

In mirror-reading, words are read from right to left and letters are read in a reverse right-to-left orientation. In one experiment we compared the ability of normal right- and left-handed subjects to mirror-read and found that the left-handers made fewer errors and could read mirror print more rapidly. In a second experiment we attempted to learn whether there is a hemifield superiority for reading mirror words and whether there are any differences between left- and right-handers in a hemifield. We found that although both right- and left-handers more rapidly detected mirror words projected to the left visual half-field, there were no differences between groups. However, in the right visual half-field, the performance of left-handers was superior to that of the right-handers. The results of the hemifield study suggest that left-handers may be superior at reading mirror words because they can more easily reverse their scanning pattern.     

Effects of intertrial interval, orientation, and adaptation on orientation discrimination measured with a yes-no signal detection paradigm

This paper describes a performance measure of lateral dominance, the Target Tests, which provides separate assessments of manual speed and accuracy within a relatively simple paper-and-pencil format. The Target Tests were administered to 111 normal adults, and scores were examined with respect to handedness, familial left-handedness, and sex. The tests significantly differentiated between right- and left-handers. Target scores were substantially correlated with the Harris Tests of Lateral Dominance, suggesting adequate reliability and validity. The means, standard deviations, and ranges for the preferred and nonpreferred hands for both handedness groups were nearly identical. The Target Tests provide a convenient instrument for assessing motoric lateralization of speed and accuracy in clinical and research settings.     

Asymmetrical Body Perception: A Possible Role for Neural Body Representations

ABSTRACT— Perception of one's body is related not only to the physical appearance of the body, but also to the neural representation of the body. The brain contains many body maps that systematically differ between right- and left-handed people. In general, the cortical representations of the right arm and right hand tend to be of greater area in the left hemisphere than in the right hemisphere for right-handed people, whereas these cortical representations tend to be symmetrical across hemispheres for left-handers. We took advantage of these naturally occurring differences and examined perceived arm length in right- and left-handed people. When looking at each arm and hand individually, right-handed participants perceived their right arms and right hands to be longer than their left arms and left hands, whereas left-handed participants perceived both arms accurately. These experiments reveal a possible relationship between implicit body maps in the brain and conscious perception of the body.