Hand dominance influences the processing of observed bodies

In motor tasks, subgroups of lefthanders have been shown to differ in the distribution of attention about their own bodies. The present experiment examined whether similar attentional biases also apply when processing observed bodies. Sixteen right handers (RHs), 22 consistent left handers (CLHs) and 11 relatively ambidextrous inconsistent left handers (ILHs) performed an own body transformation task in which they were instructed to make speeded left–right judgements about a schematic human figure. Attentional biases associated with handedness were found to extend to observed bodies: CLHs’ judgements were faster to the figure’s left side, while ILHs, like RHs, showed facilitated performance to the figure’s right side. These results demonstrate a novel embodiment effect whereby the processing of a static schematic human figure is modulated by an individual’s personal motor capabilities. This finding suggests that motor simulation may contribute to whole body perception in the absence of actual or implied actions.     

Handedness and footedness: relations to differences in sprinting speed and multiple sprints performance in prepubertal boys

Physical performance and movement skills are differentiated by brain hemispheric dominance. Relations of handedness and footedness to differences in sprint speed and multiple sprints performances were investigated in 362 prepubertal, male, novice wrestlers. Participants with two months of irregular training experience were grouped by hand and foot preferences and matched on age and anthropometry. Mean running speed was associated with the number of sprints and handedness, but not with footedness. The decrease in sprint speed was less for right-handed subjects, who also had better sprinting speed and multiple sprint performance. Symmetrical arm and leg strength development for left-handers should be emphasized.     

MRI Asymmetries of Broca''s Area: The Pars Triangularis and Pars Opercularis

Broca's area, which includes the pars triangularis (PTR) and pars opercularis (POP), is a neuroanatomic region important in speech-language production. Previous data demonstrated that PTR asymmetries are highly correlated with language dominance determined by selective hemispheric anesthesia or Wada testing, suggesting that asymmetries of the PTR may, in part, predict language dominance. The POP, however, has not been measured on volumetric magnetic resonance imaging (MRI), and therefore, it is unclear whether morphological asymmetries of the POP exist, and whether these asymmetries differ in right- and left-handers. The purpose of this study was to determine if measurable asymmetries of the POP exist on MRI, and whether the direction of the asymmetries differ in right- and left-handers. The PTR and POP were measured on volumetric MRI scans of 16 right-handers and 16 left-handers matched for age and gender. There was a significant leftward asymmetry of the PTR in right- and left-handers, although the asymmetry was reduced in the left-handers. In contrast, there was a leftward asymmetry of the POP in right-handers, and a rightward asymmetry in the left-handers. Handedness, derived from a handedness inventory, was positively correlated with POP asymmetry.     

Does degree of asymmetry relate to performance? An investigation of word recognition and reading in consistent and mixed handers

Is it advantageous to be strongly lateralized? The current study investigated this question by examining the relationship between visual field asymmetries for lexical tasks and reading performance in a sample of 200 young adults. Larger visual field asymmetries were associated with better reading performance, but this relationship was obtained primarily in those with strong and consistent hand preferences. Among mixed handers, variation in visual field asymmetry accounted for little or no variance in reading skill. In addition, correlations between visual field asymmetry and reading performance were observed for word recognition tasks, but not for tasks requiring controlled semantic retrieval. The results are consistent with the idea that consistent and mixed handers may represent differing neurobehavioral populations. Because greater lateralization was associated with better reading skill only for consistent handers, reduced behavioral asymmetry cannot be assumed to be a risk factor for reading dysfunction in the population as a whole.     

Dichotic listening performance and writing posture in right- and left-handers

Right-handers and left-handers with the inverted (IN) and noninverted (NI) writing posture were tested on a dichotic consonant-vowel listening task and on two motor tasks (hand strength and speed of tapping). The results failed to show the differences between IN and NI right-handers reported by S. M. Tapley and M. P. Bryden (1983, Neuropsychologia, 21, 129-138) and there were no significant handedness x writing posture x ear interactions. A significant interaction between dichotic listening performance and writing posture was found; NI right-handers and IN left-handers had more correct responses and fewer intrusions than IN right-handers and NI left-handers. Left-handers and right-handers were found to have a right ear advantage (REA) in the dichotic listening task but left-handers had relatively smaller left/right differences in all of the performance measures. Sample characteristics suggest that there are more IN male right-handers than IN female right-handers.     

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.     

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.     

Behavioral asymmetries of psychomotor performance in rhesus monkeys (Macaca mulatta): a dissociation between hand preference and skill.

Hand preferences were recorded for 35 rhesus monkeys (Macaca mulatta) as they manipulated a joystick in response to 2 computerized tasks. These preferences were then used to contrast 8 left- and 10 right-handed subjects on performance measures of hand skill. Individual hand preferences were found, but no significant population asymmetry was observed across the sample. However, the performance data reveal substantial benefits of right-handedness for joystick manipulation, as this group of monkeys mastered the 2 psychomotor tasks significantly faster than did their left-handed counterparts. The data support earlier reports of a right-hand advantage for joystick manipulation and also support the importance of distinguishing between hand preference and manual performance in research on functional asymmetries.     

Lateralized concomitants of human handedness

Literature was reviewed concerning lateral asymmetries of brain and behavior in normal and pathological populations of left-and right-handers. Cerebral asymmetries of structure and function are less pronounced in left-handers as a group than in right-handers as a group, and variability is greater in left-handers.     

Skill, strength, handedness, and fatigue

Thirty male subjects, 20 of whom were self-classified left-handers and 10 right-handers, were tested on a grip-strength task and a handwriting task with each hand, both under normal conditions and in a situation of induced experimental fatigue. On the basis of questionnaire scores, the left-handers were sub-divided into two groups comprising the 10 most left-handed and the 10 least left-handed subjects. The test of grip strength showed a small but significant deterioration in performance of both hands from fatigue. With the handwriting task, a similar significantly adverse effect of fatigue was recorded for all groups as well as a large significant difference in performance between the preferred and nonpreferred hands under normal conditions, which decreased under fatigue. An explanation of these differential effects is discussed in terms of the greater efficiency of the preferred hand in the highly developed skill of handwriting.     

Preferences for skill versus chance-determined activities: The influence of gender and task sex-typing

Three experiments tested the hypothesis that skill-chance activity preference by men and women is moderated by task sex relatedness. Men and women (total N = 368) opted to perform either skill or chance versions of masculine and feminine tasks, and then provided ratings of performance expectancy, importance of success, and perceptions of task characteristics. Results support the conclusion that men do not prefer skill and women chance as had been found previously, but rather that while men's skill preferences are higher than women's on a masculine taks, women prefer skill more than do men on a feminine task. Skill-chance preferences were primarily a function of the expectancy of success on skill tasks.     

Effects of Fencing Training on Motor Performance and Asymmetry Vary With Handedness

Abstract

Previous studies showed that motor asymmetries are reduced in left-handers and after a long-term fencing training in right-handers. Interestingly, left-handed athletes are substantially over-represented in elite fencing. These findings have been speculatively explained by imbalance in experience of fighting opposite handedness opponents resulted from skewed distribution of handedness, i.e. lefties encounter more righties than righties encounter lefties. Whereas these assumptions could be accurate, the underlying mechanisms remain ambiguous. In this study, we investigated effects of fencing training on motor performance and asymmetry with respect to handedness. We compared fencing performance of left- and right-handed fencers in both training and combat conditions. In the combat condition, left-handers won seven out of twelve matches consisted of twelve bouts each. They also showed a significantly longer hit detection time, a measure indicating better quality of fencing attack. In the training condition, left-handed fencers completed fencing board tests significantly faster than right-handers. These findings provide additional factor of superior motor performance to be considered when interpreting over-representation of lefties in elite fencing. Furthermore, our left-handers were less lateralized, which could explain that superior motor performance. This idea is consistent with previous findings of reduced asymmetry in right-handed fencers when comparing to non-athletes.     

Parent-offspring conflict over mating: Testing the tradeoffs hypothesis

The difference in genetic relatedness between parents and offspring results into traits such as beauty being more beneficial in a spouse than in an in-law. As a consequence, mate and in-law preferences do not overlap, and each party tends to prefer more the traits that give it more benefits. This paper tests the hypothesis that this divergence in preferences interacts with the tradeoffs nature of mating to give rise to parent-offspring conflict over mating. In particular, using a design where mate choice is constrained by a budget, three hypotheses are tested: First, asymmetries between in-law and mate preferences result in asymmetrical compromises in the choice of an in-law and a spouse. Second, the hypothesis is tested that when choice is constrained, disagreement spreads to traits where there is no divergence between in-law and mate preferences. Finally, it is hypothesized that there is a negative relationship between mate value and parent-offspring conflict over mating. Evidence from two independent studies in two different countries provides support for all three hypotheses.     

Lateral preference profiles and right shift attempt histories of consistent and inconsistent left-handers

Differences in abilities and preferences exist between left-handers who both write and throw with their left hands (consistent left-handers) and those who write with their left hand but prefer to throw with their right (inconsistent left-handers). It is also known that many left-handers are pressured to switch to right-hand writing, and that these pressures can lead to a right shift attempt. The present study is the first to explore the joint effects of the consistent/inconsistent left-handedness dichotomy, right shift attempt history, and lateral preference profiles. Testing 379 Canadian adults between the ages of 18 and 94 indicated that, while both types of left-handers were equally likely to experience a right shift attempt, the inconsistent left-handers were more likely to successfully switch to right-hand writing. Further analyses revealed that throwing hand was more associated than writing hand with the direction of sidedness for a lateral preference index based upon eye, foot, and ear preferences. More specifically, right-hand throwers were much more likely to have a rightward lateral preference score than were left-hand throwers, regardless of current preferred writing hand. Overall, the results support an hypothesis that the left-handers who are least likely to submit to rightward switch pressures are those with the strongest, most consistent left-sided lateral preference profile.     

Handedness and Reach-to-Place Kinematics in Adults: Left-Handers Are Not Reversed Right-Handers

The primary goal of this study was to examine the relations between limb control and handedness in adults. Participants were categorized as left or right handed for analyses using the Edinburgh Handedness Inventory. Three-dimensional recordings were made of each arm on two reach-to-place tasks: adults reached to a ball and placed it into the opening of a toy (fitting task), or reached to a Cheerio inside a cup, which they placed on a designated mark after each trial (cup task). We hypothesized that limb control and handedness were related, and we predicted that we would observe side differences favoring the dominant limb based on the dynamic dominance hypothesis of motor lateralization. Specifically, we predicted that the dominant limb would be straighter and smoother on both tasks compared with the nondominant limb (i.e., right arm in right-handers and left arm in left-handers). Our results only partially supported these predictions for right-handers, but not for left-handers. When differences between hands were observed, the right hand was favored regardless of handedness group. Our findings suggest that left-handers are not reversed right-handers when compared on interlimb kinematics for reach-to-place tasks, and reaffirm that task selection is critical when evaluating manual asymmetries.     

Mental rotation and handedness: differences in object-based and egocentric transformations

This study investigates mental rotation performance of right- and left-handers in object-based and egocentric mental rotation tasks using human body stimuli with an outstretched arm in front and back view. Previous literature suggests that right-handers show a slightly better mental rotation performance than left-handers. 42 participants, 14 left-handers and 28 right-handers, completed a mental rotation task with object-based and egocentric transformation of a human figure which was displayed either in front or back view. The main result was a three-way interaction between the factors “kind of transformation”, “handedness” and “view” in a way, that right-handers show significantly faster reaction times then left-handers in front view object-based transformations because of the additional in-depth rotation for front view stimuli. This difference disappeared in egocentric tasks due to the modification of onés own perspective to solve the task. The results of this study show that right-handers not generally outperform left-handers in mental rotation tasks but only if more cognitive resources are needed.     

Perceptual asymmetries in left- and right-handers for cartoon and real faces

We examined 40 left-handers and 40 right-handers on two free-vision tests of face processing. A chimeric face composed of a smiling half-face joined to either a neutral half-face (real faces) or a sad half-face (cartoon faces) and its mirror image were presented on each trial. Subjects judged which chimeric face looked happier, the one with the smile to the left or the one with the smile to the right. Right-handers, but not left-handers, had a highly significant leftward attentional bias, since chimeras with the smile to the left were judged happier than those with the smile to the right. The cartoon- and real-face tasks did not differ in the mean perceptual asymmetries they elicited. However, correlations between attentional-asymmetry scores for the two tasks, although high for both left- and right-handers, were significantly smaller than task reliabilities. Thus, the cartoon- and real-face tasks overlap to a major extent in the lateralized processes they measure, but to a lesser extent, they also index different lateralized processes.     

The effects of fluent levels of Big 6 + 6 skill elements on functional motor skills with children with autism

Functional motor skills are often taught using chaining procedures. Research suggests that chaining procedures are not likely to be effective if they do not focus on the accuracy and speed of composite skill completion. Precision teaching (PT) research suggests that improved performance of a composite skill can be achieved if the performance speed of the component behaviors is increased. This study assessed the effects of repeated timed practice of component motor skills on speed and accuracy of composite skills and the effects of fluent component motor skills on the completion of daily living composite skills. Three children with autism participated. The results suggest that all participants were able to perform the component skills at their individual aims and performed most of the component skills at fluent levels as assessed by retention and endurance checks. Each participant increased the number of composite skill steps performed independently and one decreased the overall time to complete the composite skill. Copyright © 2010 John Wiley & Sons, Ltd.     

The use of bouts and frequencies in the evaluation of hand preferences for a coordinated bimanual task in chimpanzees (Pan troglodytes): an empirical study comparing two different indices of laterality

Hand preferences for a coordinated bimanual task were assessed in 109 chimpanzees (Pan troglodytes). Hand preference was evaluated for 4 test sessions using bouts and frequencies of hand use to compare the sensitivity of each level of analysis in evaluating individual variation in handedness. Overall, significant population-level right-handedness was found using several different measures of hand use. Handedness indices based on bouts and frequencies were highly and significantly correlated. Moreover, hand preferences were consistent across tests despite efforts to situationally bias preference during each test. Taken together, these data do not support the view that bouts are a better level of analysis for evaluating hand preference. The results further suggest that hand preferences for coordinated bimanual actions are not influenced by situational factors and may reflect an inherent specialization of the left hemisphere for motor skill.