Right hemisphere specialization for color detection

Three experiments were carried out to investigate hemispheric asymmetry in color processing among normal participants. In Experiment 1, it was shown that the reaction times (RTs) of the dominant and non-dominant hands assessed using a visual target presented at the central visual field, were not significantly different. In Experiment 2, RTs of ipsilateral hands to lateralized chromatic stimuli revealed that the processing time was 17 ms shorter in the right hemisphere (RH) than that in the left hemisphere among the right-handed participants, whereas no significant difference was found among the left-handed participants. On the other hand, RTs to lateralized achromatic stimuli showed no such asymmetry among both the right- and left-handed participants (Experiment 3). These findings strongly suggest RH superiority for detection of color among right-handed individuals.     

Intrahemispheric response competition between vocal and unimanual performances in normam adult human males.

Subjects balanced a dowel rod vertically on the left and right index finger singly and while simultaneously repeating phrases. With right-handed subjects who had no left-handed relatives, concurrent verbalization shortened right- but not left-handed balancing. Increased phonetic difficulty of the phrases produced an increased decrement on right-handed balancing, but left-handed balancing was unchanged; it also produced more verbalization errors on trials with the right hand, but not with the left. Concurrent verbalization shortened balancing duration with both hands of left-handers. Right-handers with left-handed relatives produced variable results. Concurrent humming also selectively interfered with right-handed balancing. It was concluded that the results conform to an interpretation based on intrahemispheric interference between incompatible, simultaneously produced sets of responses.     

Functional lateralization of the human premotor cortex during sequential movements

A neurological truism is that each side of the brain controls movements on the opposite side of the body. Yet some left hemisphere brain lesions cause bilateral impairment of complex motor function and/or ideomotor apraxia. We report that the left dorsal premotor cortex of normal right-handed people plays a fundamental role in sequential movement of both right and left hands. Subjects performed sequential finger movements during functional magnetic resonance imaging of the motor cortices. In right-handed subjects, the volume of activated dorsal premotor cortex showed a left hemispheric predominance during hand movements. We suggest that the observed left premotor dominance contributes to the lateralization found in lesion studies.     

Manual asymmetry in weight discrimination: hand or spatial-field advantage?

Sixty subjects who were either left-handed or right-handed performed one-handed weight discrimination using their left and right hands in the left and right spatial fields. Differential thresholds, for the left and right hands of both left-handed and right-handed subjects, were found to be lower in the spatial field contralateral to the ear which proved superior in a dichotic listening test. It is concluded that manual asymmetry for weight discrimination results primarily from the mapping of sensorimotor events in the spatial fields onto contralateral cerebral cortex, with an advantage in the spatial field contralateral to the nonlanguage cerebral hemisphere.     

Asymmetrical transfer of training between hands: implications for interhemispheric communication in normal brain

Two experiments are presented which investigated claims of asymmetrical transfer of training between the hands/hemispheres. In Experiment 1, 96 right- and left-handed male undergraduates practiced an inverted-reversed printing task with either the right or the left hand. Transfer to the opposite hand was then compared to same-hand transfer, in a between-subject design. In Experiment 2, 176 right-handed boys and girls were tested at ages 7, 9, and 11 years. For right-handed subjects in both experiments, the left hand benefited more from opposite-hand training than did the right. The reverse was true for left-handers in Experiment 1, although one group (who wrote with the "inverted" position) showed little transfer in either direction. Two current models of interhemispheric interaction do not satisfactorily explain these findings. A third model, based on cross-activation, may provide a more effective alternative.     

Cerebral Organization of Motor Programming and Verbal Processing as a Function of Degree of Hand Preference and Familial Sinistrality

Seventy-six right- and left-handed subjects responded to monaurally presented verbal stimuli (CVs) using their right and left hands on separate occasions. Both degree of hand preference and familial sinistrality (FS) were taken into account. It was found that, contrary to expectation, the manual response interfered with the verbal perception task, but only in the consistent strong handers. The pattern of interference suggests that those with a consistent hand preference (right or left) have general motor programming in the left hemisphere. Those with an inconsistent strong hand preference probably have some degree of general motor programming in both hemispheres. No effect for FS was found for the lateralization of verbal processing or general motor programming.     

Aesthetic preference and lateral dominance

Aesthetic preferences for photographs with the main focal content either to the left or right of the photograph's center were examined in right- and left-handed subjects. Verbal responses or manual responses were required. In one experiment with 261 introductory psychology student-subjects, left-handers more often preferred photographs with the more important part on the left ("left-geared") than did right-handers. Exp. 2, involving 84 right-handed student subjects, showed that left-geared photographs presented on the left side were preferred more often than left-geared photographs presented on the right side, and left-geared photographs presented on the left side were more often chosen when a left-handed manual response was required. Interactions between handedness, position of the stimulus, language hemisphere, and response mode make it extremely difficult to ascertain whether the right hemisphere is really more involved in aesthetic decisions.     

Is there an effect of handedness on the position of the egocentric reference?

Forty normal subjects (20 left-handed; 20 right-handed) were submitted to a proprioceptive straight ahead pointing task while blindfolded to study the effect of the hand used and of the hand preference on the estimation of the subjective sagittal middle. Results showed that left-handed and right-handed subjects both deviated to the left of the objective sagittal middle and presented an effect of the hand used and of the starting point affecting their straight ahead performance in a similar way. In all subjects whatever their manual preference, using the left hand and starting 30 degrees to left induced a tendency to deviate to the same side, whereas using the right hand and starting 30 degrees to right induced a tendency to place the subjective middle to the right of the objective middle. These results are interpreted with regard to the hypothesis of a cortical control of the position of the egocentric reference.     

Right-left discrimination: effects of handedness and educational background

The present study investigated right left discrimination, with a paper-and-pen test with cartoon figures. The test consisted of line drawings of a person with no, one, or both arms crossing the vertical axis of the body in the figure. The subjects' task was to mark with a pencil, as fast as possible, which was the right or left hand in the figure. The line drawings were viewed from the back, from the front, or randomly alternating between the back and front views. Two studies were conducted. The first consisted of 393 adults: 153 males and 240 females; 338 right-handers and 55 left-handers. The results showed that the males performed better than the females. The left-handers and the right-handers performed equally well. However, the left-handed males performed better than the right-handed males. There was no difference in performance between the right-handed and the left-handed females. The second study consisted of 175 right-handed college students: 63 psychology students. 54 medical students, and 58 law students. The main finding was that the medical students performed better than the psychology students for all figure orientation subtests and for all arm positions. In comparison with the law students, the medical students performed at the same level on the back view subtest, but they performed better on the front view subtest and on two out of three arm positions on the alternating view subtest.     

Lateralization of bilateral transfer of visuomotor information in right-handers and left-handers

The author examined the lateralization of transfer of visuomotor information between the right and left hands during unimanual finger-tapping sequences with visual feedback. The finger-tapping task consisted of a target peak force of 2 N and a target intertap interval of 500 ms. Twenty right-handed and 10 left-handed participants performed the motor task, with 3 transfer trials following 3 practice trials. The author observed positive transfers from the left to the right hand for right-handers but the opposite direction of positive transfers for left-handers. However, left-handers showed a less variable peak force than right-handers did. The author discusses left-handers' interhemispheric information processing.     

Inter-hemispheric remapping between arm proprioception and vision of the hand is disrupted by single pulse TMS on the left parietal cortex

Parietal cortical areas are involved in sensori-motor transformations for their respective contralateral hemifield/body. When arms of the subjects are crossed while their gaze is fixed straight ahead, vision of the hand is processed by the hemisphere ipsilateral to the arm position and proprioception of the arm by the contralateral hemisphere. It induces interhemispheric transfer and remapping. Our objective was to investigate whether a single pulse TMS applied to the left parietal cortical area would disturb interhemispheric remapping in a similar case, and would increase a simple reaction time (RT) with respect to a control single pulse TMS applied to the frontal cortical area. Two LED were superimposed and located in front of the subjects on the saggital axis. Subjects were asked to carefully fixate on these LED during each trial. The lighting of the red LED was used as a warning signal. Following the green one was illuminated after a variable delay and served as a go-signal. The hand for the response was determined before the start of each trial. TMS was applied to the left parietal, the left frontal cortical areas, or not applied to the subject. Results revealed that: (1) Irrespective of its location, single pulse TMS induced a non-specific effect similar to a startle reflex and reduced RT substantially (15 ms on average) with respect to a control condition without TMS (mean value = 153 ms). (2) Irrespective of TMS, RT were shorter when the right or the left hand was positioned in the right visual hemi-field (i.e. normal and crossed positions respectively). (3) Finally, RT increased when single pulse TMS was applied to the left parietal area and when hands were crossed irrespective of which hand was used. We concluded that interhemispheric sensori-motor remapping was disrupted by a single pulse TMS that was applied to the left parietal cortex. This effect was also combined with some visual attention directed towards the hand located on the right visual hemi-field.     

Encouraging pointing with the right hand,but not the left hand,gives right-handed 3-year-olds a linguistic advantage

Previous research has shown a strong positive association between right-handed gesturing and vocabulary development. However, the causal nature of this relationship remains unclear. In the current study, we tested whether gesturing with the right hand enhances linguistic processing in the left hemisphere, which is contralateral to the right hand. We manipulated the gesture hand children used in pointing tasks to test whether it would affect their performance. In either a linguistic task (verb learning) or a non-linguistic control task (memory), 131 typically developing right-handed 3-year-olds were encouraged to use either their right hand or left hand to respond. While encouraging children to use a specific hand to indicate their responses had no effect on memory performance, encouraging children to use the right hand to respond, compared to the left hand, significantly improved their verb learning performance. This study is the first to show that manipulating the hand with which children are encouraged to gesture gives them a linguistic advantage. Language lateralization in healthy right-handed children typically involves a dominant left hemisphere. Producing right-handed gestures may therefore lead to increased activation in the left hemisphere which may, in turn, facilitate forming and accessing lexical representations. It is important to note that this study manipulated gesture handedness among right-handers and does therefore not support the practice of encouraging children to become right-handed in manual activities.

Research Highlights

• Right-handed 3-year-olds were instructed to point to indicate their answers exclusively with their right or left hand in either a memory or verb learning task.
• Right-handed pointing was associated with improved verb generalization performance, but not improved memory performance.
• Thus, gesturing with the right hand, compared to the left hand, gives right-handed 3-year-olds an advantage in a linguistic but not a non-linguistic task.
• Right-handed pointing might lead to increased activation in the left hemisphere and facilitate forming and accessing lexical representations.

     

Generalizing everyday memory: Signs and handedness

Memory for frequently encountered road signs was investigated. In Experiment 1, the average level of recall of road sign features was found to be only 47%. In Experiment 2, more left-handed than righthanded people recalled that a walking figure faces right on one sign, whereas more right-handed than left-handed people recalled that a digging figure faces left on another sign. Performance thus reflected not a difference in level of mnemonic ability between left-handed and right-handed groups but instead the compatibility between group and task. In Experiment 3, participants were asked to draw any figure walking and any figure digging, with a pattern of results similar to that of Experiment 2. It is suggested that handedness effects in recall are mediated by motor imagery.     

Hemispheric specialization for reading

Behavioral laterality tasks with linguistic stimuli were used to assess the differential processing efficiencies of the cerebral hemispheres in right- and left-handed adults. Findings from a lateralized lexical decision task with concrete nouns supported Zaidel's (1983) "direct access" model of hemispheric functioning. A dual task consisting of oral and silent reading indicated that the right hand was significantly more disrupted than the left during unimanual finger tapping; however, some bilateral interference was observed. Taken together the findings suggest that although the left hemisphere was relatively more efficient, the right hemisphere was dynamically involved in the reading process.     

Ratings of emotion in laterally presented faces: sex and handedness effects

Sixteen right-handed participants (8 male and 8 female students) and 16 left-handed participants (8 male and 8 female students) were presented with cartoon faces expressing emotions ranging from extremely positive to extremely negative. A forced-choice paradigm was used in which the participants were asked to rate the faces as either positive or negative. Compared to men, women rated faces more positively, especially in response to right visual field presentations. Women rated neutral and mildly positive faces more positively in the right than in the left visual field, whereas men rated these faces consistently across visual fields. Handedness did not affect the ratings of emotion. The data suggest a positive emotional bias of the left hemisphere in women.     

Apraxia in a patient with atypical cerebral dominance

Liepmann postulated that the left hemisphere of right-handed persons contains the "movement formulas" that control purposeful skilled movements of the limbs on both sides of the body. Accordingly, in right-handers apraxia should follow damage to the left hemisphere, whereas right hemisphere damage should not lead to apraxia. Although this is generally true, we recently examined a right-handed man who after a right hemispheric stroke became aphasic and apraxic with his nonparalyzed right hand. Our observations suggest that the right hemisphere of this right-handed man made a critical contribution to the planning and execution of skilled movements. This case provides evidence that right-handers should not be considered a homogeneous group in terms of cerebral motor dominance and that contrary to Liepmann's postulate, hemispheric dominance for the control of skilled movements does not entirely determine handedness.     

Control of interjoint coordination in the performance of manual circular movements can explain lateral specialization

Between-arm performance asymmetry can be seen in different arm movements requiring specific interjoint coordination to generate the desired hand trajectory. In the current investigation, we assessed between-arm asymmetry of shoulder-elbow coordination and its stability in the performance of circular movements. Participants were 16 healthy right-handed university students. The task consisted of performing cyclic circular movements with either the dominant right arm or the nondominant left arm at movement frequencies ranging from 40% of maximum to maximum frequency in steps of 15%. Kinematic analysis of shoulder and elbow motions was performed through an optoelectronic system in the three-dimensional space. Results showed that as movement frequency increased circularity of left arm movements diminished, taking an elliptical shape, becoming significantly different from the right arm at higher movement frequencies. Shoulder-elbow coordination was found to be asymmetric between the two arms across movement frequencies, with lower shoulder-elbow angle coefficients and higher relative phase for the left compared to the right arm. Results also revealed greater variability of left arm movements in all variables assessed, an outcome observed from low to high movement frequencies. From these findings, we propose that specialization of the left cerebral hemisphere for motor control resides in its higher capacity to generate appropriate and stable interjoint coordination leading to the planned hand trajectory.     

Lifted-weight difference thresholds as a function of hand

A study was conducted to determine if the two hands of right-handers are differentially sensitive to changes in perceived weight. Using the method of limits, the left and right hands of 20 college students were tested at each of three reference weights: 90, 100, and 110 gm. Results indicated that, over-all, difference thresholds for the two hands were not reliably different, though a trend did emerge toward greater right-handed sensitivity to weight changes at smaller weights and greater left-handed sensitivity at greater weights.     

The effects of movement direction and hemispace on estimates of distance traveled

BACKGROUND/HYPOTHESIS: The degree of attention directed to a stimulus and the presence of anisometric representations can alter the perception of the magnitude of a stimulus. We wanted to learn if normal right-handed subjects' estimates of distance traveled are influenced by the right-left direction or hemispace of movements. METHODS: We had blindfolded participants estimate the distance their arm was moved in a rightward or leftward direction, in right and left hemispace. Since we wanted subjects to estimate the distance traveled rather than compute the distance between the start and finish points, the subjects' arms were passively moved in sinusoidal trajectories at a constant speed. RESULTS: Subjects estimated leftward movements as longer than rightward movements, but there was no effect of hemispace. COMMENTS/CONCLUSIONS: People often attend more to novel than routine conditions and therefore participants might have overestimated the distance associated with leftward versus rightward movement because right-handed people more frequently move their right hand in a rightward direction and learn to read and write using rightward movements. Thus, leftward movements might be more novel and more attended than rightward movements and this enhanced directional attention might have influenced estimates of magnitude (distance).