Manual asymmetries in the temporal and spatial control of aimed movements

Right-handed participants performed aimed, left- and right-hand movements toward a fixed target in speed and precision conditions. The purpose was to determine detailed hand differences in the temporal and spatial control during the course of a movement. The results showed that hand differences pertaining to spatial control of movement direction occurred throughout movement execution, and that these differences were stronger in the high speed and low precision conditions. Furthermore, the left hand took more time to execute a movement than the right hand, especially in conditions of low speed and high precision. Detailed time analysis revealed that slowing down of the left hand specifically happened prior to peak acceleration and beyond peak deceleration. These detailed temporal hand differences reoccurred as additional discontinuities in the acceleration profile. These results suggest that the left hand has more difficulty at movement start than the right hand, possibly in overcoming initial inertia. It is discussed whether time-based manual asymmetries located near the end of movement execution should be explained in terms of increased feedback use, or should be related to hand differences regarding the possible active dissipation of mechanical energy at movement completion.     

Attending to the non-preferred hand improves bimanual coordination in children

The effect of attentional focus in bimanual coordination was investigated from a developmental perspective by examining performance of right- and left-handed children, 5-8-years and 9-12-years old, on bimanual reciprocal tapping tasks. Attentional focus was either specified, by asking the children to attend to the preferred or to the non-preferred hand, or unspecified for the execution of the tasks. When attention was oriented to the non-preferred hand we found a reduced movement time and a lower frequency of errors. Performance differences for handedness and age-groups were observed when the children were oriented to attend to the preferred hand or when there was no instruction regarding attention. These differences in performance were eliminated when attention was oriented to the non-preferred hand.     

Haptic Discrimination of Nonsense Shapes: Hand Exploratory Strategies but Not Accuracy Reveal Laterality Effects

Studies on haptic processing show inconsistent results concerning sex and hand differences. We present a novel approach in which manual exploratory strategies were examined. Twenty-four right-handed adults of both sexes had to monohaptically explore unseen meaningless stimuli and then to recognize their visually presented outline drawings among drawings of different stimuli. Tactual stimuli were composed of eight smoothly joined cubes whose junctions were not haptically discernible. The computer recorded number and duration of hand contacts on each cube. Analyses included the accuracy of the recognition phase, the number and duration of exhaustive explorations of the stimulus, and the number of cubes simultaneously touched. Neither hand nor sex differences were found for the accuracy measurement. The number and duration of exhaustive explorations also provide no evidence of hand differences. However, the left hand touched simultaneously more cubes than the right and this asymmetry was more pronounced in males than in females. Such an asymmetry was apparent in the very first contact of the hand with the shape. It is suggested that exploratory strategies may be more sensitive measures in revealing hand lateralization than the accuracy measurement.     

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.     

Sampling frequency and the study of eye-hand coordination in aiming

This study synchronized sampling of point of gaze (PG) and hand movements in a fast aiming task, using a 60- and a 120-Hz sampling frequency. The subjects moved eyes, head, hand, and trunk freely. For limb kinematics, a significant difference between sampling conditions was only found for the number of accelerations in the profile following peak velocity of the hand. For PG movements, no differences were found for initiation time, saccade angle, fixation duration, and overall number of saccades. However, significant differences were observed for saccade duration. Previously, an invariant feature was found for the ratio of PG and hand response times (50%). For both sampling frequencies, a significant correlation and, thus, temporal coupling was found between PG response time and time to peak acceleration for the hand. Depending on the measures required, a 60-Hz sampling of PG and hand movements may provide as meaningful results as a 120-Hz sampling.     

Accommodation to increased accuracy demands by the right and left hands

This study was designed to identify the phase of rapid aimed movements responsible for hand differences in motor skill, and to evaluate potential differences between the hands in accommodating to greater accuracy demands. In both experiments, an accelerometer mounted on a stylus allowed key changes in acceleration to be used to partition the movement into phases. In Experiment 1, slower left hand movement times were attributable primarily to a terminal homing-in phase, especially as target size decreased. Since error rates varied as a function of hand and target size, speed-accuracy trade-offs may have occurred. Experiment 2 rigidly controlled error rate and confirmed the major hand difference to occur in the latter phase of the movement where error correction is presumed. Although less pronounced, adjustments were made in the earlier movement phases as well. Accommodation to greater accuracy demands involved moving the stylus closer to the target before decelerating to engage in error correction. This adjustment to gain enhanced precision was more pronounced in the left hand.     

Evidence for cerebral asymmetries in a finger sequencing task

Visual input was lateralized using a specially designed contact lens system. Subjects performed a sequence of two keypresses in response to a light stimulus with either the left or the right hand in a choice reaction time paradigm. Two choice reaction time conditions were used: (A) hand certainty, sequence uncertainty and (B) hand uncertainty, sequence certainty. Reaction time (RT) results indicate that there are no significant differences between the left and right hemisphere in selecting a sequential response in either of the two conditions. Interfinger time (IFT) results show a relative left eye (right hemisphere)-left hand advantage when there was hand certainty, sequence uncertainty and a relative left eye (right hemisphere) disadvantage for both hands when there was hand uncertainty, sequence certainty. The RT results do not support the concept of a center in the left hemisphere for selection of the components of a two-element sequential keypress, prior to movement initiation. However, the IFT results indicate that there are differences in the processing ability of the left and right hemispheres in a sequencing task, after movement initiation.     

Accommodation to Increased Accuracy Demands by the Right and Left Hands

This study was designed to identify the phase of rapid aimed movements responsible for hand differences in motor skill, and to evaluate potential differences between the hands in accommodating to greater accuracy demands. In both experiments, an accelerometer mounted on a stylus allowed key changes in acceleration to be used to partition the movement into phases. In Experiment 1, slower left hand movement times were attributable primarily to a terminal homing-in phase, especially as target size decreased. Since error rates varied as a function of hand and target size, speed-accuracy trade-offs may have occurred. Experiment 2 rigidly controlled error rate and confirmed the major hand difference to occur in the latter phase of the movement where error correction is presumed. Although less pronounced, adjustments were made in the earlier movement phases as well. Accommodation to greater accuracy demands involved moving the stylus closer to the target before decelerating to engage in error correction. This adjustment to gain enhanced precision was more pronounced in the left hand.     

Asymmetrical hand usage in infancy: An ethological approach

Observations of the motor behavior of 22 infants were made by 8-hour daily video recording of nursery school activity over 11 days. Recorded object-oriented manipulating or holding actions were scored as the number of movements made by each hand separately and together, by each child, each day, and the average duration of hand activity. For the group, the right hand made significantly more movements than the left, and the duration of right-hand use was longer than the left. Although individual differences in frequency of hand use were reliably consistent, they were not for movement duration. The results show that data from spontaneous object manipulation can be a highly reliable and valid means of assessing differences in hand usage.     

Hand-movement profiles in a tactual—tactual matching task: Effects of spatial factors and laterality

We examined the effect of spatial factors and hemispheric lateralization upon hand-scanning strategies in 14 right-handed men tested in a tactual—tactual matching task. The experiment involved comparisons (judgments of same or different) between two objects sequentially touched by the fingertips of the left or right hand. Stimuli were made of smoothly joined cubes whose junctions were not haptically discernible. Exploratory strategies were inferred from the durations and locations of hand contacts with any of the cubes composing the stimuli. Accuracy was greater when the same stimulus was touched twice by the same hand than when different hands were used to feel it. With regard to strategies, both hands touched the upper parts of the object longer than the lower parts. Subjects also inspected more portions of the objects ipsilateral to the hand used. Overall differences in time spent touching cubes were greater for the right hand than for the left hand, showing that touch times were less evenly distributed on object parts for the former than for the latter. In this study, the process of information gathering by touch appears to be determined by the intertwining integration of contextual factors (e.g., stimulus position in space), biomechanical constraints on hand movements, and such cognitive factors as hemispheric differences on the ability to encode spatial pattern information.     

Men and women holding hands: II. Whose hand is uppermost?

Sex differences in the way men and women hold hands were investigated in a series of six studies. Specifically, it was hypothesized that men would have the uppermost hand in male-female couples holding hands in public significantly more often than women. Also, the American couples observed in Study 1 were classified by height, those in Study 2 by age, those in Study 3 by hand preference, those in Study 4 by ethnic group, and those in Study 6 by sex of initiator of the handholding; the handholding couples in Study 5 were Japanese adults. A combined total of 15,008 handholding couples were observed in these six studies, and across differences in height, age, hand preference, ethnicity, culture, and sex of the initiator of handholding in public, men were significantly more likely than women to have the uppermost hand.     

Handedness as a function of sex and age in a large population of Lemur

A population of 194 lemurs (Lemur spp.), 116 males and 78 females, from 1 to 30 years of age, was assessed for lateralized hand use in simple food reaching with a minimum of 100 reaches per animal. A hand preference was present in 80% of the population with a bias for use of the left hand that was most characteristic of male lemurs and young lemurs. The results confirm the presence of lateralization in prosimians, and we interpret the sex and age differences in relation to current theories of neural lateralization.     

Hand preference for writing and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC internet study

In an Internet study unrelated to handedness, 134,317 female and 120,783 male participants answered a graded question as to which hand they preferred for writing. This allowed determination of hand preference patterns across 7 ethnic groups. Sex differences in left-handedness were found in 4 ethnic groups, favoring males, while no significant sex differences were found in three of the groups. Prevalence of left-handedness in the largest of the ethnic groups (self-labelled as "White") was comparable to contemporary hand preference data for this group [Gilbert, A. N., & Wysocki, C. J. (1992). Hand preference and age in the United states. Neuropsychologia, 30, 601-608] but the prevalence of left-handedness in individuals >70 years of age was considerably higher in the present study. Individuals who indicated "either" hand for writing preference had significantly lower spatial performance (mental rotation task) and significantly higher prevalence of hyperactivity, dyslexia, asthma than individuals who had clear left or right hand preferences, in support of Crow et al. [Crow, T., Crow, L., Done, D., & Leask, S. (1998). Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision. Neuropsychologia, 36, 1275-1282]. Similarly, an association of writing hand preference and non-heterosexual orientation was clearest for individuals with "either" writing hand responses. We conclude that contradictions in the literature as to whether or not these variables are linked to handedness stem largely from different definitions of hand preference. Due to a lack of statistical power in most studies in the literature, the "either" hand writing preference group that yielded the most salient results in this study is not normally available for analysis.     

The control of movement in the preferred and non-preferred hands

The nature of the difference in skill between the preferred and non-preferred hands was investigated using a peg-board task. The first experiment examined the effects of varying movement amplitude and target tolerance on performance. The difference between hands was found to be related to tolerance rather than movement amplitude. The second study analysed a film record of well-practised subjects, confirming the hypothesis that most of the difference between hands is due to relative slowness of the non-preferred hand in the positioning phase involving small corrective movements. Analysis of the type and number of errors further suggested that this result is not due to differences in duration of movements but to their increased frequency, implying greater accuracy of aiming with the preferred hand. Thus whilst the initial gross analysis implicated feedback processing in skill differences the more detailed analysis suggests that motor output of the nonpreferred hand is simply more variable.     

Intermanual Interactions During Simultaneous Execution and Programming of Finger Movements

In bimanual movements, some differences between the movements performed by the two hands cause interference, while others do not. Similarly, in choice between responses with the left and right hand some differences between the two movements increase RT, while others do not. It is suggested that both kinds of effects are, at least in part, due to the incompatibility between processes that determine characteristics of movements jointly for both hands and that are present during preparation as well as during execution. This hypothesis implies that during execution of one movement, programming of a different movement to be performed with the other hand should be impaired, as compared to a condition in which the successive movements of both hands are the same. This expectation was confirmed for finger movements of different forms where an effect on choice RT had been shown previously. On the other hand, interference between execution and programming is not to be expected when successive movements differ in characteristics that are likely to be specified separately for each hand, as indicated by a lacking effect in choice experiments. This expectation was confirmed for successive movements performed with different fingers of either hand as compared to movements performed with the same fingers.     

Hand preferences and hand ability in congenitally blind children

Congenitally blind and sighted blindfolded children between the ages of 6 and 14 years were tested for hand preference with performance tasks. There were no differences between the groups in direction or degree of hand preference. The degree of handedness increased with age and was essentially linear though the blind seemed to be somewhat less lateralized at the younger ages.

When the same groups were required to match three-dimensional bricks for height, depth, breadth, and volume, no hand advantages were found for either group. Both groups of children improved in their accuracy of spatial discriminations with age.

Further, the degree of lateralization on the handedness task did not relate to ability on the tactile task or to differences between the right and left hands on the tactile task. Thus, there is no effect of blindness on tactile matching ability nor is there an effect of the hand used in the task.     

Intermanual interactions during simultaneous execution and programming of finger movements

In bimanual movements, some differences between the movements performed by the two hands cause interference, while others do not. Similarly, in choice between responses with the left and right hand some differences between the two movements increase RT, while others do not. It is suggested that both kinds of effects are, at least in part, due to the incompatibility between processes that determine characteristics of movements jointly for both hands and that are present during preparation as well as during execution. This hypothesis implies that during execution of one movement, programming of a different movement to be performed with the other hand should be impaired, as compared to a condition in which the successive movements of both hands are the same. this expectation was confirmed for finger movements of different forms where an effect on choice RT had been shown previously. On the other hand, interference between execution and programming is not to be expected when successive movements differ in characteristics that are likely to be specified separately for each hand, as indicated by a lacking effect in choice experiments. This expectation was confirmed for successive movements performed with different fingers of either hand as compared to movements performed with the same fingers.     

Eye movements and performance during bilateral tracing tasks

To examine the role of current visual monitoring in the between-hand differences in skilled movements, eye movements and errors during bilateral tracing tasks were analyzed in 10 subjects. When subjects traced a horizontal course abductively with both hands, the subject's gaze followed the movement of the right hand, and more errors were observed on the left hand. When subjects traced a vertical course, where fine motor control for alteration of movement direction was necessary, more errors were shown on the left hand despite the alternate visual scan of the two hands. The results were interpreted as showing that the between-hand differences in skilled movements are primarily due to the left hand's poor ability in motor output, and that the differential efficiency in the use of visual monitoring becomes an important factor in the between-hand differences when symmetrical movements of both hands with a low degree of difficulty are required.     

Rightward superiority of eye movements in a bimanual aiming task

To examine the role of visual monitoring in the between-hand differences in skilled manual movements, eye movements and performance during bimanual aiming tasks were analysed. When subjects were required to make bimanual aiming responses to symmetrically placed targets, they preferentially monitored the movements of the right hand, resulting in better performance on the right hand. In addition, manipulation of the subject's gaze showed that the movements of the right hand were more influenced by visual monitoring than those of the left hand. The results were interpreted as showing that the between-hand differences in skilled movements are mainly due to the different efficiency in the use of visual monitoring.     

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.