Asymmetrical hemisphere activation enhances global–local processing

Decades of research focusing on the neurophysiological underpinnings related to global–local processing of hierarchical stimuli have associated global processing with the right hemisphere and local processing with the left hemisphere. The current experiment sought to expand this research by testing the causal contributions of hemisphere activation to global–local processing. To manipulate hemisphere activation, participants engaged in contralateral hand contractions. Then, EEG activity and attentional scope were measured. Right-hand contractions caused greater relative left-cortical activity than left-hand contractions. Participants were more narrowly focused after left-hemisphere activation than after right-hemisphere activation. Moreover, N1 amplitudes to local targets in the left hemisphere were larger after left-hemisphere activation than after right-hemisphere activation. Consistent with past research investigating hemispheric asymmetry and attentional scope, the current results suggest that manipulating left (right) hemisphere activity enhanced local (global) attentional processing.     

EEG alpha asymmetry and creativity

Results of 3 experiments examining the relationship between creativity and left-hemisphere and right-hemisphere EEG activity are reported. Creativity has been hypothesized to involve the use of primary-process cognition, and such cognition is hypothetically accompanied by activation of the right cerebral hemisphere. In light of these hypotheses, we predicted that highly-creative people should exhibit greater right-hemisphere than left-hemisphere EEG activity during creative performance and that this pattern would not be found in less-creative people. All 3 experiments supported this prediction. This difference in asymmetry was specific to creative performance. It was not present during basal recordings or during a non-creative task.     

Asymmetrical hemisphere activation enhances global–local processing

Decades of research focusing on the neurophysiological underpinnings related to global–local processing of hierarchical stimuli have associated global processing with the right hemisphere and local processing with the left hemisphere. The current experiment sought to expand this research by testing the causal contributions of hemisphere activation to global–local processing. To manipulate hemisphere activation, participants engaged in contralateral hand contractions. Then, EEG activity and attentional scope were measured. Right-hand contractions caused greater relative left-cortical activity than left-hand contractions. Participants were more narrowly focused after left-hemisphere activation than after right-hemisphere activation. Moreover, N1 amplitudes to local targets in the left hemisphere were larger after left-hemisphere activation than after right-hemisphere activation. Consistent with past research investigating hemispheric asymmetry and attentional scope, the current results suggest that manipulating left (right) hemisphere activity enhanced local (global) attentional processing.     

Reliability and Validity of a Paper-and-Pencil Test Measuring Hemisphere Preference

The present studies examined the reliability and validity of the Preference Test (PT), a widely used self-report index of preferred hemisphere thinking styles. The PT consists of items that intend to tap left-hemisphere and right-hemisphere cognitions. In the first study (N=47), PT scores were found to have reasonable test–retest stability. In the second study (N=334), a factor analysis of PT scores showed that the PT has a two-factor solution that can best be interpreted in terms of putative left- and right-hemisphere items. In the third study (N=29), background EEG activity (F3, F4, P3 and P4) of subjects was recorded. PT scores were found to be related to EEG asymmetry patterns for frontal, but not for parietal, recording sites. More specifically, subjects with a left-hemisphere preference displayed relatively stronger left frontal activity than subjects with a right-hemisphere preference. By and large, the present findings provide strong support for the reliability and some suggestive evidence for the validity of the PT.     

Language localization in cases of left temporal lobe arachnoid cyst: evidence against interhemispheric reorganization

We investigated whether left-hemisphere arachnoid cysts lead to reorganization of the language function using PET. A group analysis demonstrated that patients showed no more right-hemisphere activation than a matched control group. Several patients had clear language localizations in the left hemisphere during language comprehension; none of the patients showed right-hemisphere activation. We conclude that left-hemisphere tissue must suffer considerable compromise before reorganization of language into the right hemisphere becomes necessary. Language activations within the left hemisphere are clearly displaced. This is consistent with mere physical displacement in some patients rather than reorganization within the left hemisphere; in others intrahemispheric reorganization cannot be excluded.     

Hemisphere differences in the effects of cuing in visual recognition tasks.

In Experiment 1 uncued recognition of single letters presented in left or right visual fields showed no hemispheric asymmetry, but cuing by alternatives produced a left-hemisphere advantage. Uncued recognition of words was better in the right visual field (left hemisphere), and this advantage was unchanged by cuing by alternatives or cuing by class. In Experiment 2 a mixed series of words, digits, and dots was presented. Uncued trials showed no asymmetry, but when a precue indicated which type or stimulus would appear next, a left-hemisphere advantage for words was evident. Cuing also produced a nonsignificant shift toward a left-hemisphere advantage for digits and a right-hemisphere advantage for dots. The asymmetrical effects of cuing can be explained by Kinsbourne's attentional model of lateralization, which suggests that cuing may selectively activate one hemisphere, and so bias attention toward the contralateral visual field. Repetition effects within and between visual fields were analyzed but no asymmetries were found.     

Asymmetries in finger-tapping interference produced by mental versus manual rotation of Shepard and Metzler type objects

Two experiments were conducted using dual-task finger-tapping procedures to examine cerebral hemisphere laterization for mental versus manual rotation. Actual three-dimensional block-designs based on Shepard and Metzler's (1971) abstract three-dimensional cubes were constructed. Forty-eight right-handed introductory psychology students participated in each study. The first experiment showed greater right-hand than left-hand interference for mental rotation implicating more left-hemisphere involvement. In contrast, more left-hand than right-hand finger-tapping disruption with manual rotation was observed suggesting more right-hemisphere involvement. A second experiment was conducted to determine if the right-hemisphere involvement found with manual rotation was due to the manual activity of handling and rotating the blocks. Results showed that dual-task interference produced by irrelevant manual rotation combined with mental rotation was not lateralized. Thus, the pattern of results indicate that the manipulospatial processing required in the first experiment was responsible for the asymmetry implicating right-hemisphere involvement.     

Cerebral asymmetry in the perception of American sign language.

American Sign Language (ASL) offers a valuable opportunity for the study of cerebral asymmetries, since it incorporates both language structure and complex spatial relations: processing the former has generally been considered a left-hemisphere function, the latter, a right-hemisphere one. To study such asymmetries, congenitally deaf, native ASL users and normally-hearing English speakers unfamiliar with ASL were asked to identify four kinds of stimuli: signs from ASL, handshapes never used in ASL, Arabic digits, and random geometric forms. Stimuli were presented tachistoscopically to a visual hemifield and subjects manually responded as rapidly as possible to specified targets. Both deaf and hearing subjects showed left-visual-field (hence, presumably right-hemisphere) advantages to the signs and to the non-ASL hands. The hearing subjects, further, showed a left-hemisphere advantage to the Arabic numbers, while the deaf subjects showed no reliable visual-field differences to this material. We infer that the spatial processing required of the signs predominated over their language processing in determining the cerebral asymmetry of the deaf for these stimuli.     

Divergent Thinking Styles of the Hemispheres: How Syllogisms Are Solved during Transitory Hemisphere Suppression

Psychiatric patients solved syllogisms while recovering from transitory ictal suppression of one hemisphere by electroconvulsive therapy (ECT). The premises were familiar or unfamiliar, true or false. While the right hemisphere was suppressed, syllogisms were usually solved by theoretical, deductive reasoning even when the factual answer was known a priori, the premises were obviously false and the conclusions were absurd. While their left hemisphere was suppressed, the same subjects applied their prior knowledge; if the syllogism content was unfamiliar or false, they refused to answer. We postulate a left-hemisphere mechanism capable of decontextualized mental operations and a right-hemisphere mechanism, the operation of which is context-bound and incapable of abstraction. We show that each hemisphere tends to overextend its perspective on the problem and that in the intact brain they both contribute to an extent that depends on the characteristics of the problem at hand.     

Pattern of Neuropsychological Deficit at Age Five Years Following Neonatal Unilateral Brain Injury

The pattern of language deficit following left-hemisphere brain injury and visual/spatial deficit following right-hemisphere injury in an adult or older child is well recognized, but has been inconsistently reported following presumed neonatal brain injury. Our prospective study of 24 children at age 5 with documented neonatal unilateral brain injury lends support to the theory of hemisphere specialization at the time of birth. Twelve children who had unilateral left-hemisphere lesion were compared to 12 children with unilateral right-hemisphere lesion of similar timing and severity. Relative visual/spatial deficit following right-hemisphere lesion and receptive language deficit following left-hemisphere lesion were identified. Lateralized measures of grip strength, fine motor speed, and fine motor dexterity were not significantly different between the groups for either hand in this nonhemiparetic study sample. Only one child with a left-hemisphere lesion was left-handed, and only one child (right-lesion) had a hemiparesis.     

EEG asymmetry and sleep mentation during REM and NREM

The hypothesis that dreaming is mediated by the right hemisphere was evaluated by monitoring EEG power asymmetry during REM and NREM sleep, and obtaining mentation reports when short-term temporal shifts in the EEG indicated relative left- or right-hemispheric dominance. Content analyses provided no support for the right-hemisphere hypothesis; indeed, some scales showed higher content during relative left-hemispheric dominance. In contrast to earlier reports, no difference between REM and NREM in EEG asymmetry was observed.     

A critical boundary to the left-hemisphere advantage in visual-word processing

Two experiments explored boundary conditions for the ubiquitous left-hemisphere advantage in visual-word recognition. Subjects perceptually identified words presented directly to the left or right hemisphere. Strong left-hemisphere advantages were observed for UPPERCASE and lowercase words. However, only a weak effect was observed for AlTeRnAtInG-cAsE words, and a numerical reversal of the typical left-hemisphere advantage was observed for words in a visual prototype font (a very unfamiliar word format). Results support the theory that dissociable abstract and specific neural subsystems underlie visual-form recognition and fail to support the theory that a visual lexicon operates in the left hemisphere.     

Laterality of lesions and trait-anxiety on working memory performance

An asymmetry of anterior cerebral activation favoring the right hemisphere has been associated with dispositional negative affect including trait-anxiety, while the opposite appears true of cerebral asymmetry favoring the left hemisphere. It was hypothesized that an asymmetry of cerebral activation, as defined by scores on a measure of trait-anxiety, ipsilateral to the side of an anterior brain lesion would be associated with less efficient cognitive processing than greater activation in the hemisphere contralateral to the lesion. Patients with anterior left (n = 16) or right (n = 15) hemisphere lesions completed the State-Trait Anxiety Inventory and several neurocognitive tasks. Of the abilities tested, only Digit Span scores showed an interaction between side of lesion and presumed activation asymmetry. Patients with right- but not with left-hemisphere damage showed significant differences in working memory performance depending on the presumed direction of asymmetry of the two hemispheres, supporting the dual roles of the right hemisphere in affective processing and directed attention.     

Are variations among right-handed individuals in perceptual asymmetries caused by characteristic arousal differences between hemispheres?

We propose that much of the variance among right-handed subjects in perceptual asymmetries on standard behavioral measures of laterality arises from individual differences in characteristic patterns of asymmetric hemispheric arousal. Dextrals with large right-visual-field (RVF) advantages on a tachistoscopic syllable-identification task (assumed to reflect characteristically higher left-hemisphere than right-hemisphere arousal) outperformed those having weak or no visual-field asymmetries (assumed to reflect characteristically higher right-hemisphere than left-hemisphere arousal). The two groups were equal, however, in asymmetries of error patterns that are thought to indicate linguistic or nonlinguistic encoding strategies. For both groups, relations between visual fields in the ability to discriminate the accuracy of performance followed the pattern of syllable identification itself, suggesting that linguistic and metalinguistic processes are based on the same laterally specialized functions. Subjects with strong RVF advantages had a pessimistic bias for rating performance, and those with weak or no asymmetries had an optimistic bias, particularly for the left visual field (LVF). This is concordant with evidence that the arousal level of the right hemisphere is closely related to affective mood. Finally, consistent with the arousal model, leftward asymmetries on a free-vision face-processing task became larger as RVF advantages on the syllable task diminished and as optimistic biases for the LVF, relative to the RVF, increased.     

Hemispheric contributions to lexical ambiguity resolution: evidence from individuals with complex language impairment following left-hemisphere lesions

Nine individuals with complex language deficits following left-hemisphere cortical lesions and a matched control group (n = 9) performed speeded lexical decisions on the third word of auditory word triplets containing a lexical ambiguity. The critical conditions were concordant (e.g., coin-bank-money), discordant (e.g., river-bank-money), neutral (e.g., day-bank-money), and unrelated (e.g., river-day-money). Triplets were presented with an interstimulus interval (ISI) of 100 and 1250 ms. Overall, the left-hemisphere-damaged subjects appeared able to exhaustively access meanings for lexical ambiguities rapidly, but were unable to reduce the level of activation for contextually inappropriate meanings at both short and long ISIs, unlike control subjects. These findings are consistent with a disruption of the proposed role of the left hemisphere in selecting and suppressing meanings via contextual integration and a sparing of the right-hemisphere mechanisms responsible for maintaining alternative meanings.     

Right-hemisphere interactions in picture-word processing

The processing of pictures was investigated in three experiments which eliminated the response effects involved in naming. When a categorization task was used, clear advantages in response latency and accuracy were observed for left visual-field (LVF) presentations. This was in contrast to previous investigations which have used a naming task and which have reported right visual-field (RVF) advantages. When a distracting word was added to the display, the pattern of influence also changed from that reported previously. The use of naming tasks has indicated predominantly left-hemisphere effects, with demonstrations of interactions between pictures and words in the RVF. With a categorization task in Experiment 2, however, the only effective words were those related in meaning to the picture, and only when they were projected to the right hemisphere. The third experiment confirmed the LVF advantage for picture processing with masked displays, but found no reliable asymmetry with unmasked presentations. The pattern of semantic facilitation was also confirmed with the masked displays, but when the mask was removed an inhibition effect replaced the facilitation effect. These effects are interpreted as indicating that picture recognition is localized within the right cerebral hemisphere. It is suggested that the facilitating effect of related words is restricted to the left hemisphere because it is an effect upon recognition processes, whereas the inhibition effect reflects response competition. It is also suggested that previous reports of left-hemisphere interference effects are due to effects of response competition in naming tasks.     

Sex and coding strategy effects on reaction time to hemispheric probes

Two experiments were conducted to investigate the influence of coding instructions on cerebral laterality differences. Experiment I required 20 subjects (10 female) to use either rehearsal or imagery coding strategies in a recognition task with word probes to the right and left hemispheres. No hemispheric differences were found, but sex of subject was found to be related to coding strategy. Ten subjects (5 female) in Experiment II performed a similar task, except picture probes were used. Subjects using rehearsal coding responded faster to left-hemisphere probes, but faster to right-hemisphere probes when imagery coding was employed. The differing laterality effects in these experiments were attributed to naming responses implicitly required in Experiment II.     

Left-hemisphere activation is associated with enhanced vocal pitch error detection in musicians with absolute pitch

The ability to process auditory feedback for vocal pitch control is crucial during speaking and singing. Previous studies have suggested that musicians with absolute pitch (AP) develop specialized left-hemisphere mechanisms for pitch processing. The present study adopted an auditory feedback pitch perturbation paradigm combined with ERP recordings to test the hypothesis whether the neural mechanisms of the left-hemisphere enhance vocal pitch error detection and control in AP musicians compared with relative pitch (RP) musicians and non-musicians (NM). Results showed a stronger N1 response to pitch-shifted voice feedback in the right-hemisphere for both AP and RP musicians compared with the NM group. However, the left-hemisphere P2 component activation was greater in AP and RP musicians compared with NMs and also for the AP compared with RP musicians. The NM group was slower in generating compensatory vocal reactions to feedback pitch perturbation compared with musicians, and they failed to re-adjust their vocal pitch after the feedback perturbation was removed. These findings suggest that in the earlier stages of cortical neural processing, the right hemisphere is more active in musicians for detecting pitch changes in voice feedback. In the later stages, the left-hemisphere is more active during the processing of auditory feedback for vocal motor control and seems to involve specialized mechanisms that facilitate pitch processing in the AP compared with RP musicians. These findings indicate that the left hemisphere mechanisms of AP ability are associated with improved auditory feedback pitch processing during vocal pitch control in tasks such as speaking or singing.