Left-handed Group Research Articles

The relationship of facial asymmetry and bite force to handedness in Iraqi adult sample

Facial asymmetry is a normal finding in clinically symmetrical faces. Theasymmetry in general was either functional and/or structural in nature. The objectiveof this study was to investigate the relationship of the amount and direction of facialasymmetry in clinically symmetrical faces with class I normal occlusion tohandedness, and to discover if there is any relation of occlusal bite force withhandedness and facial asymmetry in Iraqi Arab adult sample.The sample was 60 untreated Iraqi adult persons, 30 right handers, 30 left handersand each group consisted of 15 males and 15 females, with age range 18-25 years. Foreach subject a posteroanterior radiograph was taken, and then a maximum molar biteforce was measured digitally in the first molar area on each side.All subjects of the sample showed skeletal asymmetry although they have normalocclusion and it was significantly greater in right handers than in left handers(P<0.05).Skeletal asymmetry was greater in males than females for both right and lefthanders. In right-handers, the mean facial area on the left side was significantlygreater than that on the right side (P=0.000). In left handers, the mean facial area onthe right side was found to be significantly greater than that on the left side only infemales (P=0.004).The bite force, in both right and left handed groups, was larger in males than infemales, with significant difference in right handers (P=0.03) and highly significantdifference in left handers (P=0.001).Facial dimensions tend to be larger in males than in females. Skeletal asymmetrywas present even in clinically symmetrical faces with teeth in normal occlusion and itwas highly correlated to handedness. Bite force was independent of handedness withsignificantly greater molar bite force in males than females.

Auditory Evoked Potential Mismatch Negativity in Normal-Hearing Adults.

Introduction Mismatch Negativity (MMN) corresponds to a response of the central auditory nervous system. Objective The objective of this study is to analyze MMN latencies and amplitudes in normal-hearing adults and compare the results between ears, gender and hand dominance. Methods This is a cross-sectional study. Forty subjects participated, 20 women and 20 men, aged 18 to 29 years and having normal auditory thresholds. A frequency of 1000Hz (standard stimuli) and 2000Hz (deviant stimuli) was used to evoked the MMN. Results Mean latencies in the right ear were 169.4ms and 175.3ms in the left ear, with mean amplitudes of 4.6µV in the right ear and 4.2µV in the left ear. There was no statistically significant difference between ears. The comparison of latencies between genders showed a statistically significant difference for the right ear, being higher in the men than in women. There was no significant statistical difference between ears for both right-handed and left-handed group. However, the results indicated that the latency of the right ear was significantly higher for the left handers than the right handers. We also found a significant result for the latency of the left ear, which was higher for the right handers. Conclusion It was possible to obtain references of values for the MMN. There are no differences in the MMN latencies and amplitudes between the ears. Regarding gender, the male group presented higher latencies in relation to the female group in the right ear. Some results indicate that there is a significant statistical difference of the MMN between right- and left-handed individuals.

Reduced asymmetry in motor skill learning in left-handed compared to right-handed individuals

Hemispheric specialization for motor control influences how individuals perform and adapt to goal-directed movements. In contrast to adaptation, motor skill learning involves a process wherein one learns to synthesize novel movement capabilities in absence of perturbation such that they are performed with greater accuracy, consistency and efficiency. Here, we investigated manual asymmetry in acquisition and retention of a complex motor skill that requires speed and accuracy for optimal performance in right-handed and left-handed individuals. We further determined if degree of handedness influences motor skill learning. Ten right-handed (RH) and 10 left-handed (LH) adults practiced two distinct motor skills with their dominant or nondominant arms during separate sessions two–four weeks apart. Learning was quantified by changes in the speed–accuracy tradeoff function measured at baseline and one-day retention. Manual asymmetry was evident in the RH group but not the LH group. RH group demonstrated significantly greater skill improvement for their dominant-right hand than their nondominant-left hand. In contrast, for the LH group, both dominant and nondominant hands demonstrated comparable learning. Less strongly-LH individuals (lower EHI scores) exhibited more learning of their dominant hand. These results suggest that while hemispheric specialization influences motor skill learning, these effects may be influenced by handedness.

The association between hemispheric specialization for language production and for spatial attention depends on left-hand preference strength

Cerebral lateralization for language production and spatial attention and their relationships with manual preference strength (MPS) were assessed in a sample of 293 healthy volunteers, including 151 left-handers, using fMRI during covert sentence production (PROD) and line bisection judgment (LBJ) tasks, as compared to high- and low-level reference tasks. At the group level, we found the expected complementary hemispheric specialization (HS) with leftward asymmetries for PROD within frontal and temporal regions and rightward asymmetries for LBJ within frontal and posterior occipito–parieto-temporal regions. Individual hemispheric (HLI) and regional (frontal and occipital) lateralization indices (LI) were then calculated on the activation maps for PROD and LBJ. We found a correlation between the degree of rightward cerebral asymmetry and the leftward behavioral attentional bias recorded during LBJ task. This correlation was found when LBJ-LI was computed over the hemispheres, in the frontal lobes, but not in the occipital lobes. We then investigated whether language production and spatial attention cerebral lateralization relate to each other, and whether manual preference was a variable that impacted the complementary HS of these functions. No correlation was found between spatial and language LIs in the majority of our sample of participants, including right-handers with a strong right-hand preference (sRH, n=97) and mixed-handers (MH, n=97), indicating that these functions lateralized independently. By contrast, in the group of left-handers with a strong left-hand preference (sLH, n= 99), a negative correlation was found between language and spatial lateralization. This negative correlation was found when LBJ-LI and PROD-LI were computed over the hemispheres, in the frontal lobes and between the occipital lobes for LBJ and the frontal lobes for PROD. These findings underline the importance to include sLH in the study sample to reveal the underlying mechanisms of complementary HS.

Memorization of sequences of movements of the right and left hand by right- and left-handers

We analyzed the errors of right- and left-handers when performing memorized sequences by the left or the right hand during the task which activates positional coding: after 6-10 times the order of movements changed (the positions remained the same during all task). The task was first performed by one ("initial") hand, and then by another one ("continuing"); there were 2 groups of right-handers and 2 groups of left-handers. It was found that the pattern of errors during the task performance by the initial hand is similar in right- and left-handers both for the dominant and non-dominant hand. The information about the previous positions after changing the order of elements is used in the sequences for subdominant hands and not used in the sequences for dominant ones. After changing the hand, right- and left-handers show different patterns of errors ("non-symmetrical"). Thus, the errors of right- and left-handers are "symmetrical" at the early stages of task performance, while the transfer of this motor skill in right-and left-handers occurs in different ways.

A Pilot Study on Tamoxifen Sexual Side Effects and Hand Preference in Male Breast Cancer.

Recent clinical and imaging studies suggest that sex hormones modulate sexuality according to a psychophysiologic process of lateralization of the brain, with androgens playing a greater role in sexual functioning of left hemibrain/right handedness and estrogens possibly for right hemibrain/left handedness. Based on this perspective, the current study attempted to specify the relationship between hand preference, estrogens, and sexual function in subjects with male breast cancer, taking into account the sexual side effects of tamoxifen as the agent for inhibiting estrogen action. Twenty-eight Romanian men-17 right-handed and 11 left-handed-undergoing treatment with tamoxifen for male breast cancer participated in this study. These men were assessed both prior to and during tamoxifen treatment using the International Index of Erectile Function, a standardized instrument used for the evaluation of various aspects of sexual functioning, including erectile function (EF), orgasmic function (OF), sexual desire (SD), and overall functioning (OF). A main effect for handedness was found on EF, OF, SD, and OS scales, with right-handed men showing higher functioning than left-handed men. Regarding interaction effects, the left-handed group of men showed greater decreased sexual functioning during tamoxifen (on three subscales: OF, SD, OS) compared to right-handed men. Further research should be conducted in order to support and refine this potential lateralized process of sexual neuromodulation within the brain.

Effect Of Handedness On Functional Organization Of Bimanual Isometric Handgrip

Summary The aim of this study was to examine force production during maximal isometric handgrip in unilateral (UL) and bilateral (BL) tasks in right- and left-handed subjects. Ten right-handed (RH) and 8 left-handed (LH) young men were studied. The subjects were instructed, after a command, to perform a shot-like handgrip, raising maximal force as fast as possible. Three series were performed as follows: 1) UL - right handgrip; 2) UL - left handgrip; 3) BL handgrip. We measured peak force, time to peak of force and rate of force. The BL/UL ratios for the right (R) and left (L) hand and L/R ratios for the UL and BL tasks were calculated. The L/R ratios for peak force and force rate in RH group ranged across all tasks and conditions from 0.71 to 0.75. They were significantly lower than 1 (p<0.01). These ratios did not differ significantly from 1 for LH subjects (0.98–1.02), indicating the handedness in RH group only. The BL/UL ratios for peak force were 0.89 and 0.89 in RH, suggesting symmetrical bilateral strength deficit. The magnitude of the bilateral deficit in LH group was larger for the dominant (L) hand compared to non dominant (R) hand – 0.93 and 0.97 (p<0.05) respectively, suggesting an asymmetry of bilateral deficit in LH. These ratios for time of force and rate of force indicated bilateral deficit (BD) in the dominant hand of RH group only.

Variable left-hemisphere language and orthographic lateralization reduces right-hemisphere face lateralization.

It is commonly believed that, in right-handed individuals, words and faces are processed by distinct neural systems: one in the left hemisphere (LH) for words and the other in the right hemisphere (RH) for faces. Emerging evidence suggests, however, that hemispheric selectivity for words and for faces may not be independent of each other. One recent account suggests that words become lateralized to the LH to interact more effectively with language regions, and subsequently, as a result of competition with words for representational space, faces become lateralized to the RH. On this interactive account, left-handed individuals, who as a group show greater variability with respect to hemispheric language dominance, might be expected to show greater variability in their degree of RH lateralization of faces as well. The current study uses behavioral measures and ERPs to compare the hemispheric specialization for both words and faces in right- and left-handed adult individuals. Although both right- and left-handed groups demonstrated LH over RH superiority in discrimination accuracy for words, only the right-handed group demonstrated RH over LH advantage in discrimination accuracy for faces. Consistent with this, increased right-handedness was related to an increase in RH superiority for face processing, as measured by the strength of the N170 ERP component. Interestingly, the degree of RH behavioral superiority for face processing and the amplitude of the RH N170 for faces could be predicted by the magnitude of the N170 ERP response to words in the LH. These results are discussed in terms of a theoretical account in which the typical RH face lateralization fails to emerge in individuals with atypical language lateralization because of weakened competition from the LH representation of words.

Cognitive bias, hand preference and welfare of common marmosets

Common marmosets (Callithrix jacchus) have hand preferences for grasping pieces of food and holding them while eating and these are stable throughout adult life. We report here that left-handed marmosets have negative cognitive bias compared to right-handed marmosets. Twelve marmosets were trained to expect a food reward from a bowl with a black lid and not from one with a white lid, or vice versa. In probe tests with ambiguous, grey-lidded bowls a left-handed group (N=7) were less likely to remove the lid to inspect the bowl than a right-handed group (N=5). This difference between left- and right-handed marmosets was not dependent on rate of learning, sex or age. In fact, hand-preference was not associated with rate of learning the task. Furthermore, retrospective examination of colony records of 39 marmosets revealed that more aggression was directed towards left- than right-handed marmosets. Hence, hand preference, which can be measured easily, could serve as an indicator of cognitive bias and may signal a need for particular care in laboratory environments. We explain the results by arguing that hand preference reflects more frequent (or dominant) use of the opposite hemisphere and this predisposes individuals to behave differently.

Handgrip strength dominance is associated with difference in forearm muscle size.

[Purpose] It is unknown whether handgrip strength dominance is related to the size of the forearm flexor muscles. The purpose of the present study was to investigate the relationship between side-by-side differences in handgrip strength and forearm muscle thickness. [Subjects] Thirty-one young women (26 right handed and 5 left handed) between the ages of 20 and 33 years volunteered to participate. [Methods] Two muscle thicknesses (forearm-ulna and forearm-radius muscle thicknesses) were measured using B-mode ultrasound at the anterior forearm on both sides of the body. Handgrip strength was also measured on both sides. [Results] The side-by-side difference in handgrip strength was 10.2% for the right-handed group, meaning the right hand was stronger. However, the left hand of the left-handed group was 7.8% stronger compared with their right hand. There was a significant positive correlation between side-by-side differences in handgrip strength and forearm-ulna muscle thickness (r = 0.765) and between handgrip strength and forearm-radius muscle thickness (r = 0.622). [Conclusion] Our results indicate that side-by-side differences in forearm muscle size may strongly contribute to handgrip strength dominance.

Crossmodal interference in bimanual movements: effects of abrupt visuo-motor perturbation of one hand on the other.

Studies on bimanual control inevitably deal with questions about interactions between the two effectors, mostly under conditions of sensory feedback of the same modality-usually vision-for both hands. This study used a novel paradigm in which one hand performed target-directed movements under visual control, while the other hand operated under predominantly kinesthetic control, without visual feedback. By introducing an abrupt visual feedback perturbation in the 'visible' hand, resulting in an update of its visuo-motor map, the robustness of the kinesthetic-motor map of the 'invisible' hand against interference from the visually controlled hand could be tested. Results show that the visuo-motor adaptation resulted in asymmetric directional interference: when the 'visible' right hand adapted to the perturbation, it interfered substantially more with the 'invisible' left hand (group 1) than when the left hand was under visual control and the right hand under kinesthetic control (group 2). The results support recent theories of functional lateralization postulating dominance of the right hand for trajectory control and demonstrate that on the level of arm kinematics, this interference crosses modality boundaries. Interestingly, while in most participants interference manifested itself in isodirectional deviations of the kinesthetically guided hand, the deviations in a small subsample of participants mirrored those of the visually guided hand. The results are discussed in the context of potential neural crosstalk.

Auditory middle latency responses differ in right- and left-handed subjects: an evaluation through topographic brain mapping.

To investigate the association of handedness with auditory middle latency responses (AMLRs) using topographic brain mapping by comparing amplitudes and latencies in frontocentral and hemispheric regions of interest (ROIs). The study included 44 healthy subjects with normal hearing (22 left handed and 22 right handed). AMLRs were recorded from 29 scalp electrodes in response to binaural 4-kHz tone bursts. Frontocentral ROI comparisons revealed that Pa and Pb amplitudes were significantly larger in the left-handed than the right-handed group. Topographic brain maps showed different distributions in AMLR components between the two groups. In hemispheric comparisons, Pa amplitude differed significantly across groups. A left-hemisphere emphasis of Pa was found in the right-handed group but not in the left-handed group. This study provides evidence that handedness is associated with AMLR components in frontocentral and hemispheric ROI. Handedness should be considered an essential factor in the clinical or experimental use of AMLRs.

Poster #M20 INCREASED GLYCOGEN SYNTHASE KINASE-3B (GSK-3B) EXPRESSION IN PLATELETS OF FIRST ONSET PSYCHOSIS NON-AFFECTIVE PATIENTS

We aimed to quantify specific location and reproducibility of brain activation associated with discrimination of a moving textured surface in adult healthy volunteers over a 6-month interval. A sensory stimulation device was developed to provide a texture stimulus to the fingertips at a controlled speed and pressure. Repeat measurements of regional cerebral blood flow, using positron emission tomography (PET), were obtained in 10 healthy individuals, aged 33 to 80 years (mean = 55.8 years), at scanning sessions separated by 6 months. Stimulation and rest conditions were presented to either the right, dominant (n = 5) or left non-dominant (n = 5) hand. Activation location was objectively quantified with reference to probabilistic cytoarchitectonic maps. Differences in activation over time and regions of common activation were also quantified. Participants consistently activated Brodmann areas (BA) 2, 3b and 1, somatosensory areas of postcentral gyrus, at initial and 6-month studies: 93.1% of common activation for the right-hand (RH) and 60.6% for left-hand (LH) stimulation group were in these areas. Reproducible activation in BA6, 4a and 4p was also observed for the RH group (6.8% of common activation) and LH group (39.4%). There were no sites of significant difference over time for either hand. Highly consistent location of activation over time suggests that changes in loci of activation may be confidently monitored in adults using this paradigm. Use of probabilistic cytoarchitectonic maps permitted objective quantification of the anatomical location of the core of reproducible activation.

Praxis, language, and handedness: A tricky triad

Department of Experimental Psychology, Ghent University, BelgiumOn several occasions in his excellent monograph on apraxia,Georg Goldenberg points at the relation between apraxia,aphasia, and handedness (Goldenberg, 2013b). The co-occurrences of these manifestations are believed to shedlight on their cerebral organization as well as on their mutual(in)dependence.InmycommentIwouldliketoemphasizethedifficulties associated with claims regarding relations be-tween cognitive functions and their neural correlates, inparticular when it comes to their hemispheric co-lateralization. First I will outline the stance taken by Golden-berg, then I will provide some empirical and theoretical in-sights that might hint at an alternative reading of the clinicaldata.In several chapters the question is raised whether there ex-ists an obligatory relation between apraxia and aphasia, as inright handers these symptoms occur most often followingleft hemispheric lesions. Clearly, many studies have reporteda strong association between symptoms of apraxia andaphasia and their co-occurrence even increases in clinicalstudies that use dichotomous categorizations or focus onsevere types of aphasia such as global aphasia (Duffy D Goldenberg, Hartmann, & Schlott, 2003,Goldenberg, Hermsdorfer, Glindemann, Rorden, & Karnath,2007; Wang & Goodglass, 1992). Although it seems fromthese data that most patients suffering from aphasia alsotend to show apraxia, the relation is not mandatory, anddissociations are believed to be more prominent in left-handed patients. Goldenberg devotes a separate chapter toapraxia in left handers. According to his view “the absence ofright handedness leads to a reshuffling of asymmetric brainfunctions resulting in a random distribution of their later-ality” (p. 185). This experiment of nature offers the opportu-nity to investigate what functions ‘go together’ and form anobligatory link, and what functions are independent. Gold-enberg states that if two such functions “are in fact sub-components of one overarching function, they will always belocated in the same hemisphere” (p. 186). Subsequentexploration of clinical data of left-handed patients withapraxia is taken to suggest that most left-handers do notexhibit a more symmetric organization of apraxia, but revealbilateral disturbances following unilateral lesions, just likeright-handers. Goldenberg continues to demonstrate thatleft-handed patients suffer from apraxia as a consequence ofleft or right unilateral brain damage that may or may not beaccompanied by aphasia (Goldenberg, 2013a, 2013b). Heconcludes that neither the relation between apraxia andaphasia nor between apraxia and handedness is obligatoryand that “.the laterality of apraxia can vary independentlyfrom aphasia or handedness.” (p. 190).As Goldenberg elegantly demonstrates, apraxia is not amonolithic construct but consists of several (at least partiallydissociated) symptoms flagging disturbances of an over-arching cognitivefunction calledpraxis. The same can be saidfor aphasia with respect to language. In addition to thecomposed nature of these cognitive concepts, neuroimaginghas unveiled that in normal participants tasks of praxis andlanguage typically activate clusters of regions whose laterali-zation depends on the particular subcomponent and regionunder investigation. Handedness is a multifaceted concepttoo, that varies with the method of assessment and theapplied categorization. Dividing individuals in right and lefthanders might not do justice to the complex influence of thistrait, in particular when relating handedness to asymmetry ofcognitive function. Very few right handers show right hemi-spheric language dominance, but considerably more lefthanders do. As a result, left handed groups are more likely tocontain some individuals with atypical functional asymme-tries, resulting in lower mean asymmetry scores in behavioraland functional imaging studies. Given the complexity of the

Relative effectiveness of dominant versus non-dominant hand position for rescuer's side of approach during chest compressions between right-handed and left-handed novice rescuers

IntroductionThe major components affecting high quality cardiopulmonary resuscitation (CPR) have been defined as the ability of the rescuer, hand position, position of the rescuer and victim, depth and rate of...

The cross-cultural nature of the relationship between schizotypy and mixed-handedness

Positive schizotypy is associated with non-right-handedness, which includes left- and mixed-handedness. However, because the underlying mechanisms might be different, it is important to examine whether both left- and mixed-handedness are associated with a high incidence of schizotypy. During 2009–2010, we used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess 1315 undergraduate students in Taiwan for schizotypy and the Annett handedness questionnaire to assess handedness. Among the three-way classifications based on Annett's grouping, the fully left-handed group appeared to have the lowest score of positive schizotypy; next was the fully right-handed group and then the mixed-handed. Among the three-way classifications driven from cluster analysis, mixed-handers showed highest score of positive schizotypy. When handedness was treated continuously, both direction (e.g., Hand Preference Index) and consistency (e.g., Either hand use score) indicators were significantly correlated with schizotypy. The results of regression analyses showed that the quadratic handedness measure were negatively associated with schizotypy. The results remained similar after correcting for social pressure on left-handedness. In conclusion, the relationship between schizotypy and mixed-handedness appears to be cross-cultural. The dichotomous classification of handedness, right- vs. non-right-handedness, appears to be insufficient. Additional studies on the distinct mechanisms of mixed- and left-handedness are warranted.

Social stereotyping of left-handers in Serbia

Social tolerance towards left-handed people is commonly accepted in the twenty-first century, though not universal. However, at the level of social cognition a subtle bias against this visible minority group might not have disappeared. To investigate this possibility we adopted the theoretical framework of the stereotype content model (SCM) whereby two fundamental dimensions (warmth and competence) are sufficient to explain group differences in stereotype content. We examined how a large sample of medical students (N=300) perceived nine social groups (seven with various physical, social, or mental handicaps, and the two target groups of left- and right-handers), and four “anchor” groups comprising educated people, pensioners, drug addicts, and rich people) which are considered as prototypical in terms of the SCM. Hierarchical cluster analysis was performed to determine similarity of groups in the warmth×competence two-dimensional space. Four clusters were identified, with left- and right-handers located in the same cluster together with educated people. This cluster had higher ratings on both warmth and competence (i.e., more positive stereotype) compared with all other groups. However, within-cluster analysis showed that the left-handed group was perceived as lower on both dimensions compared to the right-handed group. This statistically significant difference suggests that implicit bias against left-handed individuals has not vanished despite pervasive social tolerance. Possible mechanisms that may explain this subtle and subliminal stereotyping are discussed.

TMS stimulus–response asymmetry in left- and right-handed individuals

There have been inconsistencies in the literature regarding asymmetrical neural control and results of experiments using TMS techniques. Therefore, the aim of this study was to further our understanding of the neural relationships that may underlie performance asymmetry with respect to the distal muscles of the hand using a TMS stimulus-response curve technique. Twenty-four male subjects (12 right handed, 12 left handed) participated in a TMS stimulus-response (S-R) curve trial. Focal TMS was applied over the motor cortex to find the optimal position for the first dorsal interossei muscle and to determine rest threshold (RTh). Seven TMS intensities ranging from 90 to 150% of RTh were delivered in 10% increments. One single TMS block consisted of 16 stimuli at each intensity. Peak-to-peak amplitudes were measured and the S-R curve generated. In right-handed subjects, the mean difference in slopes between the right and left hand was -0.011±0.03, while the mean difference between hands in left-handed subjects was -0.049±0.08. Left-handed normalized data in right handers displayed a mean of 1.616±1.019 (two-tailed t test p<0.05). The left-handed group showed a significant change in the normalized slope as indicated by a mean of 1.693±0.149 (two-tailed t test p<0.00006). The results found in this study reinforce previous work which suggests that there is an asymmetry in neural drive that exists in both left- and right-handed individuals. However, the results show that the non-dominant motor hemisphere displays a greater amount of excitability than the dominant, which goes against the conventional dogma. This asymmetry indicates that the non-dominant hemisphere may have a higher level of excitation or a lower level of inhibition for both groups of participants.

Relevance of hand dominance to the bilateral deficit phenomenon

During maximal voluntary contractions, the sum of forces exerted by homonymous muscles when activated unilaterally (UL) is, typically, larger than the sum of forces when activated bilaterally (BL). This phenomenon is known as the bilateral deficit (BLD). Our purpose was to determine if the dominant limb would be inhibited to a greater degree in the BL condition, thereby reducing any disparity in force output between the limbs. Maximum voluntary handgrip strength was measured in 40 left-handed and 40 right-handed individuals under both BL and UL conditions. The right-handers displayed 10.4% greater right hand strength in both conditions; the left-handers exhibited 5.5% greater left hand strength in the UL and 4.3% in the BL condition. A BLD (-1.30%) was present in the left-handed group only but a reduction in the force disparity between the hands was not evident. It was observed, however, that seven individuals from each group exhibited greater UL force with their non-dominant hand. Accordingly, we re-analyzed the data after rearranging the groups based on unilateral hand grip strength dominance. A significant reduction in force disparity between the hands occurred for the left-handed group only, the result of a significant inhibition of the stronger left hand. A trend towards a similar reduction occurred for the right-handers because of a significant force reduction of the stronger right hand. Consequently, it appears that for maximum handgrip contractions, the BLD may be related to preferential inhibition of the stronger hand, especially for individuals who are left-hand-strength-dominant in terms of unilateral force output.

Effect of interaction between eye-hand dominance on dart skill

The purpose of this research was surveying the effect of interaction between eye hand dominance on dart skill. Twenty healthy male subjects (age: 21.43±1.33) from University of Shahid Chamran were served as the participants for this study. Subjects were divided into two groups: unilateral (right eye and right hand or left eye and left hand) group (10 subjects) and cross lateral (right eye and left hand or left eye and right hand) group (10 subjects). Each group trained for 12 sessions in the same condition. The acquisition test was made after the last training session and the retention test was made 1 week later. The scores of pre-test, acquisition and retention were recorded. Subjects threw 60 darts in each training session. Porta (Roth, 2002) and Hole in the card test (Sage, 1984) was used to select eye dominance and Edinburgh questionnaire (Oldfield, 1971) was used to determine handedness. Values of p<0.05 were chosen as significant. The results of dependent t-test (paired t-test) analysis showed that there was a significant difference between the pre-test, acquisition and retention between two groups that showed both groups learn dart skill. On the other hand, the subjects of two groups improved significantly in acquisition and retention phases rather than pre-test phase. Moreover, the results of independent t-test showed that there was no significant difference between unilateral and cross lateral in acquisition and retention tests. Our findings revealed that interaction between hand and eye dominance does not affect dart skill. Key words: Unilateral, cross lateral, dart.