Dual-task performance in right- and left-handed adults: a finger-tapping and foot-tapping study

The dual-task paradigm has been used extensively to study laterality, with concurrent verbalization interfering with right finger-tapping in right handers. Only a few studies have used this paradigm to study interference patterns in left handers and have found inconsistent results. The dual-task paradigm has not been used to study interference effects with concurrent verbalization and foot-tapping. The objective of this study was to use this paradigm to assess whether verbal interference produces different effects on finger- and foot-tapping rate for right handers as compared to left handers. 12 right-handed and 12 left-handed men were studied, each with uncrossed hand and foot dominance, i.e., all individuals were either right handed and right footed or left handed and left footed. Subjects performed finger- and foot-tapping tasks with and without verbal interference. A significant relationship was found between handedness and finger- and foot-tapping rate; individuals with a stronger right-hand preference tended to tap at a higher rate on the right side and vice-versa. Analogous relationships were not found when participants were tapping and speaking concurrently. With verbal interference, both right and left handers had a significant asymmetric effect with a decremental response in right finger-tapping rate and a facilitative effect on left finger-tapping rate. In contrast, there was a bilateral decremental response in foot-tapping with verbal interference in both right and left handers. The implications of these findings are discussed with reference to cerebral laterality of language systems and to the differential organization and integration of the motor representations of the hand and the foot.     

Sensitivity to laterality as a function of handedness

This study tested the hypothesis that left-handed individuals are more aware than right-handed individuals of others' handedness. 18 left-handed and 18 right-handed college students were shown a drawing of 8 children at a party. Seven children held objects in the left hand, while one held an object in the right hand. After 2 1/2 min. the drawing was removed and subjects answered 15 questions about its contents. Included were 2 questions asking how many children were holding something in the right or left hand. Compared with right-handed subjects, left-handed subjects reported significantly more children holding something in the left hand and significantly fewer holding something in the right hand. The two groups did not differ on any other questions.     

Asymmetrical Body Perception: A Possible Role for Neural Body Representations

ABSTRACT— Perception of one's body is related not only to the physical appearance of the body, but also to the neural representation of the body. The brain contains many body maps that systematically differ between right- and left-handed people. In general, the cortical representations of the right arm and right hand tend to be of greater area in the left hemisphere than in the right hemisphere for right-handed people, whereas these cortical representations tend to be symmetrical across hemispheres for left-handers. We took advantage of these naturally occurring differences and examined perceived arm length in right- and left-handed people. When looking at each arm and hand individually, right-handed participants perceived their right arms and right hands to be longer than their left arms and left hands, whereas left-handed participants perceived both arms accurately. These experiments reveal a possible relationship between implicit body maps in the brain and conscious perception of the body.     

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.     

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.     

Right visual field advantage for perceived contrast: correlation with an auditory bias and handedness

Studies have suggested that supramodal attentional resources are biased rightward due to asymmetric spatial fields of the two hemispheres. This bias has been observed especially in right-handed subjects. We presented left and right-handed subjects with brief uniform grey visual stimuli in either the left or right visual hemifield. Consistent with the proposed asymmetry in attentional resources, right-handed subjects estimated right hemifield targets as having a higher contrast than physically identical stimuli presented in the left hemifield. Left-handed participants did not show a systematic rightward or leftward bias. However, the group of left-handed participants also took part in a dichotic listening experiment whose results showed that visual bias score correlated positively with ear-advantage in dichotic listening. Our results are consistent with the view that supramodal processing resources are biased towards the right hemispace, and that this bias is influenced by handedness.     

Right visual field advantage for perceived contrast: Correlation with an auditory bias and handedness

Studies have suggested that supramodal attentional resources are biased rightward due to asymmetric spatial fields of the two hemispheres. This bias has been observed especially in right-handed subjects. We presented left and right-handed subjects with brief uniform grey visual stimuli in either the left or right visual hemifield. Consistent with the proposed asymmetry in attentional resources, right-handed subjects estimated right hemifield targets as having a higher contrast than physically identical stimuli presented in the left hemifield. Left-handed participants did not show a systematic rightward or leftward bias. However, the group of left-handed participants also took part in a dichotic listening experiment whose results showed that visual bias score correlated positively with ear-advantage in dichotic listening. Our results are consistent with the view that supramodal processing resources are biased towards the right hemispace, and that this bias is influenced by handedness.     

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.     

Laterality, hand preference, and human spatial ability.

6 left-handed females scored significantly below 60 right-handed females on a test of spatial visualization (p less than .005). 13 left-handed males showed a higher mean score than 33 right-handed males on the spatial test, although this difference was not statistically significant. These results are consistent with the hypothesis that the left cerebral hemisphere is of greater relative importance to spatial functioning in females than males.     

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.     

Adapting chronometric tests for field studies of cognitive ability

This study was designed to examine the relationship of hand preference to performance on a thumb-positioning task. Two hypotheses were proposed on the basis of hemispheric lateralization. The first stated that all subjects would perform the task more accurately using the left thumb, regardless of hand preference. The second hypothesis tested was that left-handed subjects would perform more accurately than right-handed subjects. Each of 20 neurologically intact adults grouped by hand preference reproduced a criterion thumb position with both thumbs simultaneously. Absolute error, recorded for each movement and analyzed by mixed analysis of variance, did support the first hypothesis. However, the left-handed group did not perform statistically differently from right-handed subjects. Factors influencing the data are discussed and recommendations for further studies are made.     

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.     

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.     

Synchronization error in bilateral simultaneous flexion of elbows.

Using 7 left- and 7 right-handed subjects, the difference in time between left and right arms in the initiation of bilateral simultaneous flexion of elbows (synchronization error) was measured under three conditions: response to a sound stimulus with a warning signal, response to a sound stimulus without a warning signal, and self-initiated trial (option). The absolute value of synchronization errors depended upon experimental conditions. In conditions 'with warning' and 'option' the dominance shown in performance of left-handed subjects was the mirror-image of that shown by the right-handed subjects. The right biceps muscle responded faster in left-handed subjects and vice versa. Right-handed subjects showed rather a constant value in their dispersion of synchronization errors.     

Velocities of motor and sensory nerve conduction are the same for right and left arms in right- and left-handed normal subjects

The velocities of motor and sensory conduction of median and ulnar nerves were measured on the left and right arms of 33 right-handed and 12 left-handed normal subjects. Contrary to current knowledge there was no statistically significant difference in the velocities of nerve conduction on the left and right sides of these subjects. It was suggested that the differences in the velocities of nerve conduction cannot contribute to the mechanisms of handedness.     

Hemispheric differences in a letter classification task

The experiment examined hemispheric differences in same-different judgments for unilaterally presented letter pairs which could be classified as “same” on the basis of name identity (NI, e.g., Aa) or physical identity (PI, e.g., AA). Two groups of Ss were tested, a right-handed group and a predominantly left-handed group. The experiment employed a reaction time measure, and fixed the duration of brief exposures to yield an overall performance level of 90% correct. Analysis of the results focused on the difference between RTs for the NI matches and for the PI matches in each hemisphere. The method allowed differences in cognitive processing to be assessed while sensory and response factors were minimized. The right-handed group all showed a smaller mean NI-PI difference in the left hemisphere (84 msec) than in the right hemisphere (181 msec). The left-handed group showed smaller and less consistent differences, but the group as a whole had a reversed asymmetry, with a mean NI-PI difference of 128 msee in the left hemisphere and 90 msec in the right hemisphere.     

Visual on- and off-latencies and handedness

Ten Ss served in this experiment, five right-handed and five left-handed. Every S was tested in a perceived-order situation and by the up-and-down method to determine the relative on-latency for a visual test stimulus. i.e, (ON-Lat for lest stimulus involving right hemisphere- ON-Lat for standard stimulus involving left hemisphere) and to determine a similarly defined relative off-latency for the same test stimulus. The algebraic difference between the relative on-latency measure and the relative off-latency measure was then found. Data from a previous study had suggested that this “on-off difference” was characteristically positive for left-handed Ss and negative for right-handed Ss. The present data agree. The left-handed Ss were found to differ significantly from the right-handed Ss in the magnitude of the on-off difference. This outcome appears important as a possible clue to functional interhemispheric differences related to handedness.     

Relations among hand preference,craniofacial asymmetry,and ear advantage in young subjects

The relations for hand preference with craniofacial asymmetry and ear advantage, and between craniofacial asymmetry and ear advantage were investigated in young healthy subjects. Ear advantage was recorded as duration of hearing, craniofacial asymmetry by computerized tomography in 44 right-handed and 38 left-handed male and female high school students. Right-handers had a right ear advantage and a larger left craniofacial region, whereas left-handers had a left ear advantage and a larger right craniofacial region. These results are consistent with the speculation that hand preference may be related to craniofacial and consequently aural asymmetries.     

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.     

Bilateral electrodermal activity in waking man

Skin conductance responses were examined bilaterally in a group of 14 normal subjects. Twelve of them were right-handed and two were left-handed. All right-handed subjects exhibited asymmetry in skin conductance level and in skin conductance response during verbal-numerical and visual-imagery tasks. With the visual activity, larger responses were found in the left hand, while during the verbal task, larger responses were recorded from the right hand. The results were interpreted as evidence of hemispheric asymmetry of the electrodermal activity orienting response control mechanisms. More ipsilateral control for the right hand is predicted.