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Motor performance as a function of verbal, nonverbal interference and handedness.

The effect of verbal and nonverbal interference on finger-tapping performance was analyzed in self-classified left (n = 15) and right-handed (n = 15) subjects. Data were analyzed with a Group (left hander, right hander) x Condition (with interference [verbal, nonverbal], without interference) x Hand (left hand, right hand) mixed factorial ANOVA with repeated measures in Condition and Hand factors. Verbal as well as nonverbal interference conditions, as compared to non-interference conditions, significantly impaired finger-tapping performance of the left relative to right handers.

Adult↗

Handedness and bilateral femoral bone densities in men and women.

To examine the relation of hand preference to bilateral femoral bone mineral density (BMD), the right and left total and regional (neck, trochanter, intertrochanteric, and Ward's triangle) proximal femur BMDs (g/cm2) were measured using dual-energy X-ray absorbtiometry (DEXA) in 32 right- and 26 left-handed university students. The mean total BMD of the total right-handers and the mean trochanteric BMD of the right- handed males were greater in the left femur than the right femur. Contrarily, the total left-handers had higher mean intertrochanteric BMD in the right side than in the left side. There were negative correlations between R-L BMD differences and Geschwind scores of total, male, and female subjects. The results suggest that femur-BMD may be related to hand preference.

Absorptiometry, Photon↗

Does handedness determine which hand leads in a bimanual task?

Right- and left-handers (n = 16 in each group) were tested on a bimanual circle task that required drawing either in the same direction (parallel) or in a mirror symmetrical coordination mode with the two hands. The authors' primary purposes were to examine the effect of circle direction on within-hand and between-hands variables and to determine whether the relation between hand lead and coordination mode (parallel or mirror symmetrical) differs for left- and right-handers. A strong relation was found between lead hand and movement condition, which depended on the direction of the movements and whether the task was parallel or mirror symmetrical. The pattern of results was similar for left- and right-handers on parallel tasks, but group differences were found with respect to mirror symmetrical tasks. At odds with the general claim that the dominant hand leads, the present results indicated that hand dominance does not generally determine which hand leads.

Adolescent↗

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.

Journal Article↗

Handedness and hemispheric asymmetry in the control of movements.

This study investigated the influence of hemispheric specialization of function on the motor performance of the hands. Right-handed (n=7), ambidextral (n=21), and ambisinistral (n=12) subjects performed Fitts' (1954) reciprocal tapping task under two conditions with each hand. Conditions had the same index of difficulty but differed in movement precision. The left hand of right-handers was superior in the condition requiring the greatest amount of preprogramming. Conversely, the right hand was not superior in the condition having the greatest demand for feedback control. For ambidextrals, left-hand superiority in the relatively preprogrammed condition was also revealed. Ambisinistrals showed no significant difference between conditions with either hand. The results partially support the hypothesis that the motor performance of the hands mirrors the dominant processing mode of their contralateral hemisphere. Failure to find supportive evidence in ambisinistrals is consistent with the contention that they lack hemispheric specialization of function.

Journal Article↗

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.

Journal Article↗

Association between familial sinistrality and pathological left-handedness: a comparison of mentally retarded and nonretarded subjects.

The hypothesis that familial sinistrality (FS) might be a useful variable for differentiating between pathological and natural left-handers was explored. A comparison of the incidence of FS in mentally retarded and nonretarded samples indicated that a positive history of familial sinistrality (FS+) was significantly more likely to occur in mildly retarded individuals. In addition, left-handed retarded people, in general, were significantly more likely to be FS+ than were right-handed retarded people.

Adolescent↗

Handedness and performance variability as factors influencing mirror movement occurrence.

A finger flexion task was used to investigate the effect of hand preference and performance variability on intensity of mirror movement. Right- and left-handed subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50, or 75% of their maximum strength capacity for the active finger. Greater mirror movement occurred when the small finger was active, and where there was greater variability in task performance, while mirror movement intensity was less when the dominant hand and the index finger were active. These findings were consistent with the cortical activation explanation of motor overflow (Todor & Lazarus, 1986a), and suggest that task variability is an important factor influencing motor overflow production. It was concluded that, if performance variability reflects the efficiency of cortical activation underlying control of a voluntary task, then refined cortical control decreases the potential for motor overflow to occur. However, it is necessary to clarify the relationship between hand preference, performance variability, and motor overflow, perhaps by examining the neural pathways involved in motor overflow production.

Adult↗

Handedness and its association with gender-related psychological and physiological characteristics.

Prenatal exposure to a high level of testosterone is thought to result in sinistrality and increased masculinization in females. This paper seeks to determine whether sinistral females show more masculine characteristics relative to dextral females. Demonstration of such a relationship would support the proposition that testosterone affects laterality. Masculine and feminine personality characteristics, breast size, age at menarche, and regularity of menstruation were measured via a questionnaire administered to 40 dextral and 40 sinistral female university students. Sinistrals were found to score significantly higher on the masculine subscale and lower on the feminine subscale of the Bem Sex Role Inventory relative to their dextral counterparts. No differences were found between the groups for breast size, menstrual regularity, or age at menarche. These results demonstrate that hand preference is associated with gender-related psychological characteristics, but not the physiological characteristics measured. Thus, the possibility that the different sex roles adopted by sinistrals and dextrals is the result of socialisation rather than biological mechanisms, such as testosterone, cannot be ruled out.

Adult↗

Measuring handedness: a validation study of Bishop's reaching card test.

The aim of the study was the validation of Bishop's reaching card test (Bishop et al., 1996) in a French population. Annett's peg-moving test (1985) and the Purdue pegboard (Tiffin, 1948) were also used to assess manual performance. Subgroups of left- and right-handers were established according to manual preference as measured by Annett's questionnaire (1985). A sample of 260 adults was tested, including 158 self-professed right-handers, 77 self-professed left-handers, and 25 self-professed ambidextrous people. The three manual performance tests and the questionnaire presented good metric qualities (homogeneity, test-retest reliability). However the constitution of subgroups of laterality (in particular left-handers) as a function of manual preference could not be validated by classic tasks, or by Bishop's test, which is supposed to combine features of both preference and performance. Moreover the link between performance and preference was weak. Both evaluations should be used to produce a complete pattern of laterality for each participant.

Journal Article↗

Handedness, measures of hemispheric asymmetry, and lateralised lexical decision.

The goals of the present study were to evaluate the differences between measures of lateralisation in the human brain derived from a dichotic listening (DL) task and from a task involving identification of visually presented consonant-vowel-consonant (CVC) nonwords, and to correlate these lateralisation indices with performance on a lexical decision task involving visually presented words and nonwords. Visual stimuli were presented either in a central position, or to the left or right of fixation. Left-handed and right-handed participants completed each of the three tasks. Lateralisation indices were derived from performance on the DL and CVC tasks, and latency and accuracy measures of lexical decision performance were obtained for targets presented centrally and parafoveally. Lateralisation indices for left-handed and right-handed participants differed significantly for both tasks, and the two lateralisation indices had different pattern of correlation with lexical decision performance for left- and right-handers. For left-handers, lateralisation indices derived from the (visual) CVC task were correlated with lexical decision response latency for targets in central and left visual field. For right-handers, lateralisation indices derived from the (auditory) DL task were correlated with lexical decision response latency for targets in central and right visual field. A possible explanation for this finding is that the two laterality measures reflect specialisation for different types of linguistic processing in the human brain.

Journal Article↗

Gödel, Escher, and degree of handedness: differences in interhemispheric interaction predict differences in understanding self-reference.

Ramachandran (1995) theorised that the left hemisphere (LH) is specialised for making a single and consistent interpretation of the self and the world, whereas the right hemisphere (RH) is responsible for monitoring anomalies in reference to these interpretations. If the anomalous information reaches a threshold, it interacts with the LH to update these interpretations or beliefs. Because mixed handers may have greater degrees of interhemispheric interaction compared to strong handers, they may have a lower threshold for updating beliefs. Two previous studies found this to be the case (Niebauer, Aselage, & Schutte, 2002a; Niebauer, Christman, & Reid, 2002b). Because monitoring one's beliefs may involve metacognitive processes, i.e., cognitions about cognitions, this model was extended to help explain individual differences in understanding self-referential concepts. In the first two studies, mixed-handed participants displayed a greater understanding of self-reference using a conceptual description of Gödel's Incompleteness Theorem. In a third study, mixed-handed participants displayed greater appreciation for self-referential works of M. C. Escher. Implications for a neuropsychological model of metacognition are discussed.

Adult↗

Reaching patterns across working space: the effects of handedness, task demands, and comfort levels.

Two experiments are reported which examine skill demands, location, and perceived comfort levels for a preferential reaching test with left- and right-handed participants. In Experiment 1, the effect of task demands was examined by having participants perform tasks of varying difficulty with tools (Lift, Pantomime, and Use) that were placed in an array in working space. Preferred hand reaches predominated at the midline and ipsilateral positions, and decreased significantly for contralateral positions, where the frequency of preferred hand reaches increased with task difficulty. In Experiment 2 we developed a new measure (the Comfort Rating Scale) to rate the subjective feeling of comfort for reaching movements. Using the same array of tools and tasks, participants were instructed which hand to use to perform reaching movements, and then rated how the movement felt. The preferred hand was always rated as being comfortable, whereas the non-preferred hand was sensitive to the effects of task demands and tool position. The ratings showed that it was the level of comfort with the non-preferred hand, rather than with the preferred hand, that contributed to the patterns seen on the first study. The Comfort Rating Scale provides new insight into the distribution of reaching movements within working space.

Adolescent↗

The modern mythology of the left-handedness of Alexander the Great.

The prevalent modern suggestion that Alexander the Great was left-handed probably derives from Michael Barsley's (1966) book, Left-handed man is a right-handed word, perhaps by mutation from as earlier story cited by Wile in 1934 from a 17th century Rabbirical exegesis, which said that Alexander discovered a country where all the inhabitants were left-handed. That itself may derive in part from the medieval Hebrew Book of Jossippon, which mentions Alexander talking of the superiority of the left hand and of how "kings stemming from the tribe of kings are left-handed".

Functional Laterality↗