Under what conditions will right-handers use their left hand? The effects of object orientation, object location, arm position, and task complexity in preferential reaching

When reaching to objects, it is known that the preferred hand is selected significantly more often for midline and ipsilateral reaches, although right-handers are more likely to continue to use their right hand to reach for an object in contralateral space (Mamolo, Roy, Rohr, & Bryden, 2006). The current study examined the influence of object orientation, object location, task complexity, and initial position of the hands on a reaching task in a sample of 45 right-handed adults. Participants reached to and picked up a mug oriented in one of three ways (handle to right, left, or neutral position) located in one of three spatial positions (left, right, and midline) from each of two starting hand positions: right hand over left, and vice versa. Along with the expected results, an interesting pattern emerged where both the orientation of the object and the position of the hands had significant effects on hand selection, such that the use of the non-preferred left hand was augmented in conditions where preferred-hand use was awkward and biomechanically inefficient. The results will be discussed in light of current theories accounting for hand selection preferences.     

Under what conditions will right-handers use their left hand? The effects of object orientation,object location,arm position,and task complexity in preferential reaching

When reaching to objects, it is known that the preferred hand is selected significantly more often for midline and ipsilateral reaches, although right-handers are more likely to continue to use their right hand to reach for an object in contralateral space (Mamolo, Roy, Rohr, & Bryden, 2006). The current study examined the influence of object orientation, object location, task complexity, and initial position of the hands on a reaching task in a sample of 45 right-handed adults. Participants reached to and picked up a mug oriented in one of three ways (handle to right, left, or neutral position) located in one of three spatial positions (left, right, and midline) from each of two starting hand positions: right hand over left, and vice versa. Along with the expected results, an interesting pattern emerged where both the orientation of the object and the position of the hands had significant effects on hand selection, such that the use of the non-preferred left hand was augmented in conditions where preferred-hand use was awkward and biomechanically inefficient. The results will be discussed in light of current theories accounting for hand selection preferences.     

How time modulates spatial responses

Behavioural evidence suggests a left-to-right directionality in the representation of elapsing time. We tested whether this representation produces a spatial attentional shift that activates a corresponding left-to-right spatial response code. Fourteen participants judged whether a cross lasted for a short (1 sec) or a long (2 sec) duration with left and right responses, respectively, or vice versa, while event-related potentials (ERPs) were measured. Responses were faster when participants judged short and long durations with their left and right hand, respectively, than vice versa. In these compatible conditions only (short-left; long-right), ERP negativity developed over the right motor scalp region around the short duration, a finding that is compatible with an early pre-activation of left-hand responses, and over the left motor region around the long duration, suggesting a later pre-activation of right hand responses. These findings confirm that in this task elapsing time is represented from left to right, and that this representation generates corresponding response codes that influence performance.     

Specialization of the right hemisphere for visuomotor control

The accuracy of saccades directed towards the remembered positions of targets in left (LVF) or right (RVF) visual hemifield was measured. The majority of right-handed subjects were found to be more accurate at directing their gaze to locations in the LVF than in the RVF, suggesting that the right hemisphere is superior to the left in oculomotor control. Even after completion of a corrective saccade following the primary saccade, subjects systematically undershot target direction and overshot target depth, suggesting that visual feedback normally plays an important role in the fine guidance of gaze after the completion of a primary saccade.     

Changes of hand preference in Parkinson’s disease

This study focused on the difference between pre-morbid and current hand preference of patients with Parkinson's disease (PD). A survey instrument comprised items measuring pre-morbid and current hand preference and question related to the side of occurrence of initial symptoms. These questions were administered to 471 PD patients. The results show a significant change of pre-morbid right hand preference toward using the left when the side of PD onset was on the right hand and vice versa. Disease duration does not predict the amount of hand preference shift.     

"Crossed homonymous hemianopia" and "crossed left hemispatial neglect" in a case of Marchiafava-Bignami disease.

"Crossed homonymous hemianopia" and "crossed left hemispatial neglect" were observed in a woman with Marchiafava-Bignami disease. Two forms of "crossed homonymous hemianopia" were observed. Initially, Goldmann perimeter testing showed a left homonymous hemianopia with the right hand and vice versa. Later, confrontation tests showed a left homonymous hemianopia, whereas visual field testing using the Goldmann perimeter (kinetic quantitative perimeter) and the OCTOPUS (Interzeag AG, static automated perimeter) showed a right homonymous hemianopia with either hand. "Crossed left hemispatial neglect" was not seen with the left hand, but neglect of the left hemifield was seen with the right hand. CT and MRI showed a lesion occupying almost the entire corpus callosum. PET showed no significant differences between comparable areas of the left and right cerebral hemispheres. These findings indicate that both signs of interhemispheric disconnection were due to the callosal lesion. Moreover, the "crossed left hemispatial neglect" can be explained as being a consequence of the dominance of the right cerebral hemisphere for visuospatial recognition.     

TASK-SPECIFIC MOTOR PERFORMANCE AND MUSCULOSKELETAL RESPONSE in SELF-CLASSIFIED RIGHT HANDERS

We examined the difference between the left and right hand motor performance (in terms of erg produced) of self-classified right handers (15 men, 15 women) for power (task involving muscle force) and skilled (task involving precision and eye hand coordination) tasks. Musculoskeletal response during task performance was measured by electromyogram to test the hypothesis that performance with the nondominant hand would trigger more generalized muscle tension. The difference between the left and right hand performance of men was nonsignificant for power task; for women, right hand performance was significantly superior than left for such task. Men excelled in power and women excelled in skilled tasks relative to their counterparts. Generalized muscle tension was significantly more during the left than the right hand performance for power but not for skilled tasks     

Task-specific motor performance and musculoskeletal response in self-classified right handers

We examined the difference between the left and right hand motor performance (in terms of erg produced) of self-classified right handers (15 men, 15 women) for power (task involving muscle force) and skilled (task involving precision and eye hand coordination) tasks. Musculoskeletal response during task performance was measured by electromyogram to test the hypothesis that performance with the nondominant hand would trigger more generalized muscle tension. The difference between the left and right hand performance of men was nonsignificant for power task; for women, right hand performance was significantly superior than left for such task. Men excelled in power and women excelled in skilled tasks relative to their counterparts. Generalized muscle tension was significantly more during the left than the right hand performance for power but not for skilled tasks.     

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.     

Arithmetic and laterality

Relationships between arithmetic ability, hand preference and hand skill were investigated in a general population sample of schoolchildren, aged 9-11 years. Incidences of non-right-handedness were highest in the children best at arithmetic and fell progressively through average and below average groups. Strong effects were found for hand skill; level of ability declined linearly from left to right across the R-L continuum in both sexes. Strong dextrality was associated with poor left hand skill and not superior right hand skill. Arithmetic ability was positively associated with left hand skill but not with right hand skill.     

Hemispheric asymmetry of ipsilateral motor cortex activation during unimanual motor tasks: further evidence for motor dominance.

OBJECTIVES: To test to which extent the increase in ipsilateral motor cortex excitability during unimanual motor tasks shows hemispheric asymmetry. METHODS: Six right-handed healthy subjects performed one of several motor tasks of different complexity (including rest) with one hand (task hand) while the other hand (non-task hand) was relaxed. Focal transcranial magnetic stimulation was applied to the motor cortex ipsilateral to the task hand and the amplitude of the motor evoked potential (MEP) in the non-task hand was measured. In one session, the task hand was the right hand, in the other session it was the left hand. The effects of motor task and side of the task hand were analyzed. Spinal motoneuron excitability was assessed using F-wave measurements. RESULTS: Motor tasks, in particular complex finger sequences, resulted in an increase in MEP amplitude in the non-task hand. This increase was significantly less when the right hand rather than the left hand was the task hand. This difference was seen only in muscles homologous to primary task muscles. The asymmetry could not be explained by changes in F-wave amplitudes. CONCLUSIONS: Hemispheric asymmetry of ipsilateral motor cortex activation either supports the idea that, in right handers, the left motor cortex is more active in ipsilateral hand movements, or alternatively, that the left motor cortex exerts more effective inhibitory control over the right motor cortex than vice versa. We suggest that hemispheric asymmetry of ipsilateral motor cortex activation is one property of motor dominance of the left motor cortex.     

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) × Condition (with interference [verbal, nonverbal], without interference) × 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.     

Spatial compatibility and anatomical factors in simple and choice reaction time

Simple reaction time to a lateralized unstructured visual stimulus was studied in subjects with hands crossed or uncrossed. Regardless of the hand position, the right hand was faster than the left hand when the stimulus was to the right of fixation, and vice versa. In both conditions there was a left visual field superiority. In a second experiment the same lateralized stimuli were presented to subjects with hands crossed or uncrossed who had to decide which hand to use depending on the position of the stimulus. In this experiment the faster hand was the one in the same visual space as the stimulus (spatial compatibility). We conclude that in simple reaction time experiments the difference between ipsilateral and contralateral reactions is due to the elementary anatomical connectivity, and that spatial compatibility becomes important only in choice situations.     

Specialization of the left hemisphere in baboon-evidence from directional preferences

Baboons which had previously learned a series of tactile discrimination tasks using only the fingers of one hand, followed by tests under the same conditions with the other hand, were tested for directional preferences in a simple perceptual-motor task. Using only the fingers of one hand the animals were allowed to rotate a disc either clockwise, or anticlockwise to receive a reward. The direction of rotation chosen by the animal was recorded. Each hand was tested separately and five sessions were given with each hand. It was found that seven out of eight monkeys preferred a flexor movement, i.e. towards the midline of the body, with the right hand and five out of eight an extensor movement with the left hand. The strong preference shown by the right hand is opposite to that seen in man whereas the left hand weakly prefers the same direction as man. A possible left hemispheric superiority in baboon for this type of task is discussed.     

Hemisphere asymmetries for imitation of novel gestures

BACKGROUND: Disorders of imitation are traditionally considered as a symptom of apraxia, but defective imitation of gestures can contrast with intact performance of gestures to verbal command and vice versa. It thus seems worthwhile to explore the neural basis of imitation of gestures independently of other manifestations of apraxia. OBJECTIVE: To assess body part specificity of disturbances of imitation for meaningless gestures of fingers, hand, and foot. METHOD: Imitation of meaningless gestures involving fingers (internal hand configuration), hand (external hand position), or foot was examined in 30 patients with left brain damage (LBD), 20 patients with right brain damage (RBD), and 20 normal control subjects. RESULTS: LBD affected imitation of hand and foot gestures more than imitation of finger gestures, whereas RBD had the strongest effect on finger gestures and affected foot gestures more than hand gestures. CONCLUSION: These results can be accounted for by the assumption that body part coding of gestures depends on left hemisphere function and that additional right hemisphere contributions are afforded when demands on perceptual discrimination rise.     

EXERTION LEVEL AND THE INTENSITY OF ASSOCIATED MOVEMENTS

Associated movements in the contralateral limbs were measured quantitatively for 42 seven- to eight-year-old children who wrote with the right hand. Associated movements of the contralateral homologous muscles systematically increased as a function of the intensity of contraction of the active hand. The associated movements were more intense when the left hand was active. The order of hand use markedly affected the lateral asymmetry, indicating that the right and left hands were affected differentially by previous activity. Associated movements of the contralateral antagonist muscles were also observed, and their frequency varied as a function of active hand and exertion level.     

Intermanual transfer effects in sequential tactuomotor learning: evidence for effector independent coding

Results from our earlier brain imaging studies regarding motor learning have shown different areas activated during naive and practiced performance. When right handed participants moved a pen either with the dominant or non-dominant hand continuously through a cut-out maze as quickly and accurately as possible, practice resulted in decreased brain activity in right premotor and parietal areas as well as left cerebellum, while increased activity was found in the supplementary motor area (SMA). These lateralized practiced-related changes in brain activation suggest effector-independent abstract coding of information. To test this hypothesis more extensively, intermanual transfer of learning was examined in 24 male and female participants (12 right- and 12 left-handed) using the same maze-learning task. It was hypothesized that if an abstract representation of the movement is learned and stored, intermanual transfer effects should be more pronounced when participants transferred to a same maze as opposed to a mirror image of the maze. Errors and velocity were measured during the following conditions: initial naive performance (Naive); after practice on the maze (Prac); during intermanual transfer to the same maze (Transfer Identical); and to the mirror maze (Transfer Mirror). Transfer direction was tested from the dominant to non-dominant hand and vice versa. No significant differences were found between right- and left-handed participants, males and females, and transfer directions. However, intermanual transfer of learning was significantly greater to the identical maze as opposed to the mirror maze. These results showed that learning was indeed taking place at an abstract effector independent level.     

The influence of current direction on phosphene thresholds evoked by transcranial magnetic stimulation.

OBJECTIVES: To quantify phosphene thresholds evoked by transcranial magnetic stimulation (TMS) in the occipital cortex as a function of induced current direction. METHODS: Phosphene thresholds were determined in 6 subjects. We compared two stimulator types (Medtronic-Dantec and Magstim) with monophasic pulses using the standard figure-of-eight coils and systematically varied hemisphere (left and right) and induced current direction (latero-medial and medio-lateral). Each measurement was made 3 times, with a new stimulation site chosen for each repetition. Only those stimulation sites were investigated where phosphenes were restricted to one visual hemifield. Coil positions were stereotactically registered. Functional magnetic resonance imaging (fMRI) of retinotopic areas was performed in 5 subjects to individually characterize the borders of visual areas; TMS stimulation sites were coregistered with respect to visual areas. RESULTS: Despite large interindividual variance we found a consistent pattern of phosphene thresholds. They were significantly lower if the direction of the induced current was oriented from lateral to medial in the occipital lobe rather than vice versa. No difference with respect to the hemisphere was found. Threshold values normalized to the square root of the stored energy in the stimulators were lower with the Medtronic-Dantec device than with the Magstim device. fMRI revealed that stimulation sites generating unilateral phosphenes were situated at V2 and V3. Variability of phosphene thresholds was low within a cortical patch of 2x2cm(2). Stimulation over V1 yields phosphenes in both visual fields. CONCLUSIONS: The excitability of visual cortical areas depends on the direction of the induced current with a preference for latero-medial currents. Although the coil positions used in this study were centered over visual areas V2 and V3, we cannot rule out the possibility that subcortical structures or V1 could actually be the main generator for phosphenes.     

Left-Hemisphere Motor Dominance in Righthandersi

Left-hemisphere dominance for motor programming was tested in two experiments by measuring acquisition and cross-hand transfer of a complex key-pressing skill in righthanded adults. In the first experiment, visual feedback was excluded to insure unilaterality of motor control. Consistent with left-hemisphere motor dominance, males showed faster acquisition with righthand training than with left hand training and greater transfer from left to right than vice versa; but females exhibited neither asymmetry. To investigate the possibility that females relied on verbal strategies to remember which keys to press and that this prevented them from showing the predicted asymmetries, the need for such strategies was reduced in a second experiment by allowing visual feedback. Although the provision of visual input may have mitigated against motor asymmetries by directly engaging both hemispheres in the task, results showed more rapid improvement in skills with the right hand than with the left for both sexes, extending evidence for left-hemisphere motor dominance to a population including females as well as males.     

The time course of spatial memory processing in the two hemispheres

Previous studies have shown that memories for positions are often distorted in systematic ways, indicating the influence of categorical positions codes which can bias responses in object-relocation tasks towards stored spatial prototypes. In the present study, we examined the time course of these categorical influences. Subjects had to relocate the position of a tachistoscopically presented dot within a circle, which could appear in either the left visual field (i.e. initially to the right hemisphere) or the right visual field (i.e. initially to the left hemisphere). Three retention intervals between presentation and relocation were used: 500, 2000 and 5000 ms. Performance was most accurate with left visual field/right hemisphere presentation. Systematic distortions were found for angular errors (dot relocations regressed towards the 45 degrees with a quadrant) as well as for radial errors (dots were replaced in the direction of the circle's circumference, and this more so when the dot was further away from the circumference). Importantly, these categorical biases became stronger with retention interval and initial left hemispheric processing. These results suggest that categorical spatial coding might be the default manner in which spatial information is remembered over time. Finally, the left hemisphere may play an important role for such a categorical spatial coding.