Left-hand Performance Research Articles

Witelson's dichhaptic task as a measure of hemispheric asymmetry in deaf and hearing populations

Specialization of the right hemisphere for spatial processing was examined in adults and in hearing and deaf children using Witelson's dichhaptic task. Right- and left-hand performance did not differ for any of the groups although a significant age difference in overall performance of hearing subjects was found. The former result calls into question the validity of Witelson's task.

Ethanol, tobacco and laterality effects on simple and complex motor performance.

Tobacco had no effect on knob turning, hand tapping, foot tapping and pursuit rotor tests in 24 right-handed men, but ethanol influenced left-hand performance more than right.

Vocal-Manual Trade-Offs In Hemispheric Sharing Of Human Performance Control

Experiment 1 established the linear ordering of performance and rated difficulty of three finger-sequencing tasks. Experiment 2 embedded these tasks within a dual-task paradigm employing vocalization of words and nonwords as concurrent activities. Concurrent vocal activity interfered with right-more than with left handed performance, and this lateralized interference effect increased monotonically with increased sequence difficulty. Results are discussed in terms of hemispheric sharing of dual task performance control.

The Influence of Brain Lateralization of Function on a Manual Skill

The present study considers the predictions of the brain lateralization of function hypothesis for the concurrent-task situation where the subject is required, to perform simultaneously a manual and a cognitive task. The manual task required the subject to successively press two keys with either the right or left hand, this being done concurrently with one of twelve different cognitive tasks. The cognitive tasks varied in terms of their verbal (left hemisphere) and non-verbal (right hemisphere) attributes. The results indicate that, for the concurrent verbal task conditions, only right-hand performance was disrupted while left-hand performance remained unchanged. For the non-verbal conditions both left and right hand performance was disrupted. These findings were interpreted in terms of brain lateralization of cognitive functions and possible hemispheric processes controlling manual performance.

Cerebral processing of speech presented monaurally to left-handed subjects.

In a series of reaction-time experiments two groups of minimal pairs of English words were presented monaurally to the right and left ears of left-handed subjects. The minimal pairs were /bit/ : bet/ and /splei : sprei/ recorded in natural speech. The group of left-handed subjects did not show any evidence of an ear-advantage on either of the two groups, indicating that the lateralization of speech perception processes could not be demonstrated using monaural stimulation. The performance of left-handers continues to give equivocal results on tests of speech lateralization processes.

Effects of Concurrent Verbal and Musical Tasks on a Unimanual Skill

Subjects balanced a dowel rod on the right or left index finger while speaking, while remaining silent, and while humming a melody. In males balancing times for the right hand decreased with concurrent verbalization. Verbalization had no effect on left hand performance in males, nor on either hand in females. Concurrent humming had no effect on performance of males or females. Poorer right hand performance by males when verbalizing is attributed to interference with right-sided motor control by the left hemisphere due to verbal activity programmed by the same hemisphere. Unimpaired right hand performance in verbalizing females suggests that the language function is less clearly lateralized in females than in males. The possibility that music may be shared by both hemispheres is discussed.

The Lateralized Effects Of Concurrent Cognitive Activity on a Unimanual Skill

Laterality studies have long been plagued by: (1) poor psychological methodology; (2) lack of specification of treatment parameters' and (3) exclusive use of left-hemisphere dependent measures. It was suspected that a recent study by Kinsbourne and Cook (1971) suffered from these faults. The present experimental findings confirm these original suspicions. Both spatial and verbal cognitive tasks were employed and comparisons made with performance during two control conditions. One was a mixed spatial-verbal activity, the other control required S to merely look at a blank card. While left-hand performance was enhanced under the verbal concurrent activities, when compared with performance under control (spatial-verbal) conditions, no other significant enhancement of performance occurred with any other concurrent activity condition. With the "No Activity Specified" control some support for the Kinsbourne study was found. However, the major finding, or implication, of this study was in demonstrating that the methodological problems outlined above cannot be ignored if worthwhile laterality studies are to be performed.

A Tapping Test in Apraxia

An enigma in understanding the mechanism of motor apraxia is why patients with disease restricted to the left hemisphere cannot imitate motions with the left hand despite intact visual motor apparatus. Liepmann suggested that motor memories are stored in the left hemisphere and that in apraxia these engrams are either destroyed or separated from the right hemisphere. If Liepmann's hypothesis is correct, then, in addition to poor performance on commands and imitation, there should be poor performance in a motor task. To ascertain if there is a motor defect of the non-paretic hand of apraxic patients, twenty apraxic patients were given a rapid finger tapping test and their performance was compared with the left hand performance of aphasic right hemiparetic non-apraxic controls. The aptaxic group performed this task significantly slower than the control group, thereby giving support to Liepmann's hypothesis of apraxia.

Right-hemisphere superiority in tactile pattern-recognition after cerebral commissurotomy: Evidence for nonverbal memory

Seven patients with presumed complete midline section of the inter-hemispheric commissures were tested for delayed matching of tactile patterns. In six of these patients, left-hand performance was unequivocally superior to right, thus demonstrating right-hemisphere specialization for the perception and recall of spatial patterns. The fact that the non-speaking right hemisphere could bridge intratrial intervals of at least 2 minutes, whereas the left hemisphere could not, shows that verbal coding is neither necessary nor sufficient for the retention of complex perceptual material. The further finding that subjects with cortical lesions but intact commissures were more proficient than the commissurotomized patients (even with the left hand) suggests that both cerebral hemispheres normally participate in such tasks, but with the right playing a preponderant role.