A cardiac measure of cerebral asymmetries in infant auditory perception.

Examined the utility of cardiac habituation response recovery as a method for assessing infant cerebral asymmetries in auditory perception in a dichotic listening test. In a within-Ss design 12 3-mo-old infants were given a series of 4 10-trial tests during which their cardiac responses were habituated to a pair of dichotic speech syllables or music notes. The 10th trial in each test was a test trial on which one ear received its habituation stimulus while the other ear received a novel stimulus of the same type as the habituation pair (speech or music). Both stimulus type and ear receiving the novel stimulus were counterbalanced across tests. Overall, Ss' cardiac responses habituated during the tests and showed differential recovery to the novel stimuli. Specifically, greater response recovery occurred when a novel speech syllable was presented to the right, than to the left ear. Conversely, greater response recovery was found when a novel music note was presented to the left than to the right ear. Results indicate that young infants show a pattern of auditory perceptual asymmetries much like that found in older children and adults. Findings are consistent with the theory that in man the left hemisphere is superior at processing speech and the right hemisphere superior with nonspeech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dichotic listening in patients with splenial and nonsplenial callosal lesions.

The authors found splenial lesions to be associated with left ear suppression in dichotic listening of consonant-vowel syllables. This was found in both a rapid presentation dichotic monitoring task and a standard dichotic listening task, ruling out attentional limitations in the processing of high stimulus loads as a confounding factor. Moreover, directed attention to the left ear did not improve left ear target detection in the patients, independent of callosal lesion location. The authors' data may indicate that auditory callosal fibers pass through the splenium more posterior than previously thought. However, further studies should investigate whether callosal fibers between primary and secondary auditory cortices, or between higher level multimodal cortices, are vital for the detection of left ear targets in dichotic listening. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure to control prepotent pathways in early stage dementia of the Alzheimer's type: Evidence from dichotic listening.

The authors examined the right ear advantage in a dichotic listening task in healthy aging and very mild and mild stages of Alzheimer's disease. Subjects were simultaneously presented 3 pairs of digits to the left and right ears (e.g., left ear: 4, 3, 1; right ear: 9, 2, 5) for immediate ordered recall. Four lists of triads were presented, varying in presentation rate between digit pairs within a triad (0.5, 1.0, 1.5, 2.0 s). Results indicated that the very mild and mild Alzheimer's groups showed a larger right ear advantage in free recall compared with the healthy controls, indicating a tendency to respond to the prepotent left hemisphere pathway for language processing. Also, the right ear advantage and proportion of switches made during recall were correlated with psychometric measures of frontal lobe function in the mild Alzheimer's group but not in the very mild or healthy control groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Consonant and vowel production of right hemisphere patients

Recent reports of subclinical phonetic deficits in posterior and most particularly in Wernicke's aphasics have challenged the traditional dichotomy which characterized speech deficits in aphasia as anterior/phonetic and posterior/phonological. It is unclear whether the basis of the phonetic deficit in posterior aphasics reflects the fact that the speech production system extends to more posterior regions of the left hemisphere than previously thought or alternatively is the result of generalized brain damage effects. The present study explores the latter possibility by investigating the patterns of speech production in right hemisphere brain-damaged, non-aphasic patients with anterior and posterior lesions. Acoustic analyses conducted on a range of consonant and vowel parameters showed differences between the speech patterns of both anterior and posterior right hemisphere patients and that of Wernicke's aphasics. These findings suggest that the subclinical deficit of Wernicke's aphasics can not simply be ascribed to a generalized brain-damage effect and raise the possibility that the right hemisphere also plays some role, if only a minor one, in the phonetic implementation of speech.     

Baseline asymmetries in brain electrical activity predict dichotic listening performance.

Forty-four right-handed participants were assessed on 2 occasions 6 weeks apart on electrophysiological measures of activation asymmetry derived from spectral estimates of electroencephalogram (EEG) alpha power in homologous scalp electrodes. Approximately 4 months following the final EEG assessment. participants were administered a dichotic listening CV-syllables task. Overall, participants exhibited a highly significant right-ear advantage. Differences among individuals in ear asymmetry were predicted by the earlier recorded electrophysiological data. Participants with greater activation in left-sided posterior temporal and parietal regions showed a larger right-ear advantage. In addition, a larger right-ear advantage was predicted by right-sided prefrontal activation. These data indicate that some of the variance in dichotic listening performance can be explained by dispositional activation asymmetries and is associated with a complex pattern of posterior and anterior activation asymmetries. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric asymmetry in Down's Syndrome children.

Examined auditory processing of linguistic stimulation presented dichotically to groups of 30 Down's Syndrome (DS) children, 20 non-DS retarded children who were MA and CA matched, and 20 MA matched nonretarded children, all of whom were right-handed. Ss completed a knowledge-of-numbers test and the Slosson Intelligence Test. They then listened to 20 trials of a dichotic message at approximately 70–75 db and repeated digits they heard. DS Ss showed a significant left ear advantage in processing the auditory linguistic material, while the other Ss showed the normal right ear advantage. Findings corroborate that having DS has a specific effect on the functional organization of the CNS auditory system. The right hemisphere may not be as efficient as the left hemisphere at language processing. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Endogenous and exogenous control of attention in dichotic listening.

Dichotic listening to verbal stimuli results in a right ear advantage (REA), indicating a left hemisphere processing superiority. The magnitude of the REA can be modulated by instructions to direct attention to the left or right ear stimulus. A previous study from our laboratory showed that presenting a prime syllable before the presentation of the dichotic syllables increases reports of the nonprimed syllable, apparently a negative priming effect that inhibits attention to the distracting prime representation. The present study combined attention instruction and priming, making up a 3 × 3 factorial design. The prime stimulus was a single consonant-vowel syllable presented binaurally just before onset of the dichotic consonant-vowel syllables. Results showed that both instructions and priming manipulations had an effect on which dichotic stimulus was selected. There was also a significant interaction between attention instruction and priming manipulation, indicating that the mechanism for instructed attention and the mechanism for negative priming work on the same level of processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional lateralization for auditory temporal processing in male and female rats.

In 3 studies, adult male rats showed significantly better discrimination of tone sequences with the right ear than with the left ear. This result parallels similar findings of left-hemisphere specialization for auditory temporal processing in humans and nonhuman primates. Furthermore, because clinical evidence supports a link between specialization of the left hemisphere for auditory temporal processing and for speech processing, these results may reflect evolutionary precursors to left-hemisphere language specialization. Because male rats showed a stronger ear advantage than female rats, the findings may relate to evidence of a stronger right ear advantage in men than in women. Finally, results suggest that neonatal handling enhances lateralization for auditory temporal processing in both sexes. Combined results implicate neuroendocrine mechanisms as important factors in the development of lateralization for auditory temporal processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long latency evoked potentials in a case of corpus callosum agenesia

Following monoaural stimulation, long latency auditory evoked potentials (LLAEPs) recorded from contralateral temporal areas have a shorter latency and larger amplitude than those recorded from the ipsilateral temporal areas. This observation agrees with the operational model drawn up in 1967 by Kimura, which assumes that only anatomically prevailing crossed auditory pathways are active during dichotic hearing, while direct pathways are inhibited. The inputs may then be conveyed to the contralateral cortex, from where they finally reach the ipsilateral temporal areas by means of interhemispheric commissures. It is this mechanism which may underline the right ear advantage for verbal stimuli and the left ear advantage for melodies observed when administering dichotic listening tasks. With the aim of verifying this hypothesis, we recorded temporal LLAEPs in a 21 year-old woman suffering from complex partial seizures, whose CT scan and MRI showed corpus callosum agenesia. Our data support the hypothesis that ipsilateral pathways are greatly inhibited by the contralateral pathways, and therefore auditory stimuli can be supposed to reach the contralateral auditory cortex from where they are transferred through the corpus callosum to the ipsilateral auditory cortex.     

Investigation of Functional Hemispheric Asymmetry of Language in Tinnitus Sufferers.

The authors tested functional hemispheric asymmetry through word dichotic listening and lateralized lexical decision tasks in tinnitus patients and controls stimulated by a continuous tinnitus-like noise to test the influence of a tinnitus-like external stimulation. A classic right-ear advantage was shown in the auditory task for all but right-ear tinnitus patients, who performed as equally badly when the stimuli were presented to the right and left ears. Concerning the visual task, all participants demonstrated the expected right visual field advantage for word stimuli. Moreover, those who submitted to external stimulation demonstrated normal asymmetric patterns. These data suggest a specific effect of tinnitus on central processing and provide evidence for a functional reorganization induced by this auditory phantom perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Verbal Dichotic Listening and Manual Performance in Children With Congenital Unilateral Brain Lesions.

The authors assessed manual performance and verbal dichotic listening performance in 16 epilepsy-free children with congenital unilateral brain lesions and normal IQ to investigate cerebral reorganization. In all children, the paretic hand had fair grip function, but reaction times were impaired, and cerebral reorganization of hand function in those with right hemiplegia was shown by the high incidence of pathological left-handedness. The dichotic listening results showed that most children with left lesions had a left ear advantage significantly related to the extent of brain damage. This finding suggests that extent of cortical damage and presence of thalamic involvement, irrespective of neuropathology, are the primary factors inducing rightward cerebral language reorganization in children with unilateral congenital brain lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dichotic listening performance in relation to callosal area on the MRI scan.

The structural model of dichotic listening performance predicts reduced left ear scores in people with left hemisphere language dominance and impairment of the corpus callosum. The prediction was tested in patients with multiple sclerosis and evidence on the basis of magnetic resonance imaging (MRI) of callosal thinning. The results are partly in accordance with the structural model but indicate an effect of attentional set that correlated with quantitative measures of preserved callosal connections. The pattern of ear advantage was reversed in a small group of non-right-handed people. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Left hemisphere advantage for classical conditioning to auditory verbal CSs: effects of nonattended extinction

The effects of brain laterality, or hemispheric asymmetry, on electrodermal classical conditioning during both attended and nonattended stimulus conditions were studied. Participants were conditioned to consonant-vowel (CV) syllables during an acquisition, or learning, phase of the experiment. During a subsequent extinction phase, the conditioned stimuli (CS) were presented in a dichotic mode of presentation. Half of the participants attended to the left ear (right hemisphere) during the extinction phase and the other half of the participants attended to the right ear (left hemisphere). The results showed effects of conditioning for all participants during the acquisition phase. During dichotic extinction, the left hemisphere group showed remaining learning effects in both the attended and nonattended conditions, whereas the right hemisphere group demonstrated conditioning only in the attended condition.     

Asymmetries of selective listening and attention switching in children.

Administered a selective listening task to 155 normal right-handed 3–12 yr old children. The stimuli consisted of dichotic digits, ranging from single pairs to strings of 4 pairs/trial. Each S attempted to focus attention on 1 ear for 8 practice trials and 28 test trials before switching attention to the opposite ear. Separate analyses of correct responses and intrusion errors yielded almost identical results: There was a significant right-ear advantage (REA) and a developmental increase in overall performance, but there was no developmental change in degree of asymmetry. The REA increased with increasing list length, but independent analyses for each list length failed to reveal any developmental changes in REA. Listening asymmetry was influenced markedly by the order in which the ears were monitored; Ss of all ages had difficulty in switching attention from right ear to left. Results support the developmental invariance hypothesis of cerebral lateralization and demonstrate that auditory asymmetry is not merely a direct reflection of some fixed structural asymmetry in the brain. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Salivary testosterone concentrations in left-handers: An association with cerebral language lateralization.

The level of testosterone exposure in early brain development may influence the direction or degree of cerebral language lateralization. Possible links between individual differences in testosterone levels and patterns of speech representation were investigated in 180 healthy young adults (97 left handed, 83 right handed) using the Fused Dichotic Words Test (T. Halwes, 1991). Among left-handed participants, significantly higher testosterone concentrations were observed in individuals with a left-ear advantage on dichotic listening than in individuals with a right-ear advantage. Among right-handed participants, the pattern of group differences in testosterone tended to be reversed, resulting in a statistically significant interaction. Results extend prior findings by S. D. Moffat and E. Hampson (see record 1996-03260-006) and raise the possibility that higher testosterone is associated with patterns of brain organization in which speech and praxic functions are lateralized to the same hemisphere. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laterality effects for musical structure processing: A dichotic listening study.

Objective: Our study investigated hemispheric lateralization for musical structure processing using a dichotic listening paradigm with music and speech. Method: Eight chord sequences and 8 spoken syllable sequences were simultaneously presented, each to 1 ear. For the musical sequences, the final chord was expected (i.e., tonic) or less expected (i.e., subdominant). In addition to tonal function, which was task irrelevant, we manipulated the final syllable and the final timbre of the sequences for the experimental task: Participants were asked to identify the final syllable (/di/, /du/) or the timbre of the final chord (Timbre A or B). Results: Our experiment revealed a left-ear advantage for the tonal function effect on spoken syllable identification. For syllables presented to the right ear, identification was faster when the final chord of the musical sequence was a tonic chord rather than a subdominant chord (i.e., musical sequences presented to the left ear). Conclusions: The present finding extends the effect of musical structure previously observed for sung and visual syllable processing to spoken syllable processing. It further suggests a right-hemispheric specialization for the processing of musical structures in healthy listeners, as previously reported for split-brain patients (Tramo & Bharucha, 1991). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of sex and sex role attributions on the ear advantage in dichotic listening.

The Bem Sex Role Inventory (BSRI) and a dichotic listening task were administered to 30 participants in order to investigate the effect of polar sex (male, female) and spectral sex (masculinity, femininity) on hemispheric interactions. The dichotic pairs consisted of the consonant-vowel syllables Bee, Dee, Gee, Pee, Tee, and Kee. Although overall performance was the same across groups, women demonstrated smaller right ear advantages than men, due primarily to smaller right ear scores. Less masculine men also had smaller right ear advantages than more masculine men, but this difference was due primarily to greater left ear scores. These results were interpreted both in terms of the callosal relay and direct access models of hemispheric processing. Based on these interpretations, it was suggested that sex and sex role attribution have similar, but not identical effects on interhemispheric relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Asymmetric effects of ovarian hormones on hemispheric activity: Evidence from dichotic and tachistoscopic tests.

Previous studies have suggested a role of endogenously cycling ovarian hormones in the modulation of perceptual asymmetries. In the present investigation, participants were given perceptual asymmetry tests including verbal and nonverbal tachistoscopic and dichotic listening tasks during the menstrual and midluteal phases of the menstrual cycle. Salivary levels of estrogen and progesterone were also measured. Analyses of performance on the tachistoscopic tests revealed that left visual field, but not right visual field, accuracy was significantly lower for both verbal and nonverbal tasks at the midluteal phase than at the menstrual phase. Right ear performance on the nonverbal dichotic test was significantly reduced at the midluteal phase. Results suggest suppression of right hemisphere processing areas and possible reduction in callosal transfer efficiency at higher levels of ovarian steroids. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Masking produced by broadband noise presented in virtual auditory space

An attempt has been made to relate the masking effects studied under dichotic listening conditions to masking seen in the free field. Rather than use a free-field masking paradigm combined with monaural and binaural listening conditions, broadband maskers presented in virtual auditory space (VAS) have been used. Two virtual locations were tested: One was the right interaural axis (+90 degrees from the anterior midline) and the other was 40 degrees right of the anterior midline. Narrow-band (critical bandwidth) dichotic and diotic maskers were also derived from the VAS masker by bandpass filtering around the test frequency. This procedure preserved the interaural differences within the critical band about the test frequency but removed information outside the critical band. Using a diotic target tone of 0.6 kHz with a narrow-band masker centered on 0.6 kHz there was an increase in signal detection in the dichotic conditions when compared to that attributable to either ear alone. Furthermore, there was no further advantage in signal detection at this target frequency when a broadband VAS masker was used. This suggests that for low-frequency targets, the binaural differences within the critical band about the target frequency are sufficient for effective unmasking. In contrast, for a target frequency of 4 kHz, a dichotic narrow-band masker resulted in a reduction in detection compared to that attributable to either ear. However, detection improved to the level attributable to the far ear when a broadband VAS masker was used. This suggests that information outside the critical band is involved in the unmasking of high-frequency targets.     

Differential neural contributions to native- and foreign-language talker identification.

Humans are remarkably adept at identifying individuals by the sound of their voice, a behavior supported by the nervous system’s ability to integrate information from voice and speech perception. Talker-identification abilities are significantly impaired when listeners are unfamiliar with the language being spoken. Recent behavioral studies describing the language-familiarity effect implicate functionally integrated neural systems for speech and voice perception, yet specific neuroscientific evidence demonstrating the basis for such integration has not yet been shown. Listeners in the present study learned to identify voices speaking a familiar (native) or unfamiliar (foreign) language. The talker-identification performance of neural circuitry in each cerebral hemisphere was assessed using dichotic listening. To determine the relative contribution of circuitry in each hemisphere to ecological (binaural) talker identification abilities, we compared the predictive capacity of dichotic performance on binaural performance across languages. Listeners’ right-ear (left hemisphere) performance was a better predictor of binaural accuracy in their native language than a foreign one. This enhanced role of the classically language-dominant left hemisphere in listeners’ native language demonstrates functionally integrated neural systems for speech and voice perception during talker identification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)