Writing induces a right hemisphere linguistic advantage in dysphonetic dyslexic children: implications for attention and capacity models of laterality

An experiment demonstrated a complete hemispheric processing reversal in 10 male, dysphonetic dyslexic children that occurred during a dichotic listening test of their verbal working memory. Requiring a written response to dichotic digits produced a right hemisphere/left ear superiority in the dysphonetic dyslexics whereas normal subjects and other dyslexics maintained a left hemisphere/right ear advantage. This reversal was unaffected by changes in task difficulty. A second experiment assessed the influence on producing the reversal of concurrent manual interference with left hemisphere verbal processing (responding orally vs. manually) and selective right hemisphere priming (Forward Writing vs. Backward Writing). The dysphonetic children reverted to a strong left hemisphere superiority when recalling the dichotic digits orally. Backward writing produced no ear advantage in either direction. The findings suggest that dysphonetic dyslexia may be related to (1) left hemisphere processing demands that exceed capacity, (2) easily activated right hemisphere processing strategies and (3) failure to coordinate linguistic processing interhemispherically. The results supported a novel hybrid conceptualization of dyslexia consisting of a synthesis of selective activation, and dual processor-limited capacity, theories.     

Electrographic correlates of lateral asymmetry in the processing of verbal and nonverbal auditory stimuli

A veraged evoked potentials (AEP) to verbal (digits) and nonverbal (clicks) auditory stimuli were recorded from left and right temporal leads in ten right-handed Ss. With dichotic presentation, there was no significant difference in accuracy of report of the clicks heard in each ear, but significantly more digits were identified correctly from the right ear than from the left. Dichotic verbal stimuli elicited AEP whose early components were of greater amplitude, and whose later components were of shorter latency, from the left hemisphere than from the right. No consistent latency or amplitude differences were observed between AEP from the left and right hemispheres when clicks were presented dichotically.     

Right hemisphere comprehension of verbs in patients with complete forebrain commissurotomy: Use of the dichotic method and manual performance

The paradigm of dichotic listening was used to investigate verbal comprehension in the right, so-called “nonverbal,” hemisphere. Verbal commands were presented to the right and left ears in the simultaneous (dichotic) paradigm. There were striking instances, especially when the left hemisphere was occupied with some extraneous task, in which the right hemisphere understood the verbal command and executed the appropriate motor responses. In those instances the left hemisphere gave no overt response. Although the left hemisphere was usually dominant, it can be nevertheless concluded that not only can the right hemisphere understand verbal commands but can also express itself manually by executing actions more complex than object retrieval or pointing. As has been known for some time, the blockage of the ipsilateral pathway seems so complete during dichotic listening in the commissurotomy patient that there is no report of the words in the left ear—only of those presented to the right. At the same time there is normal report when words are presented to the left ear alone. It was found in the present study, however, that this model is too simple and only applies to the verbal response paradigm of dichotic listening. Under circumstances of dichotic presentation where the stimulus in the left ear (ipsilateral pathway) is necessary or important to the left hemisphere for completing a task, words from both pathways are reported. One may conclude that there exists a gating mechanism in each hemisphere that controls the monitoring of each auditory pathway and the degree of ipsilateral suppression.     

An intrahemispheric integration deficit in dyslexia

In order to investigate the hypothesis that dyslexia may result from a failure of intrahemispheric integration between auditory-verbal and visual-verbal processing, a dichotic listening task and a parallel divided visual field task were administered to a group of dyslexic boys between the ages of 8 and 11 years, and a group of normal control subjects individually matched for age and WISC intelligence. The dyslexics were on average over two years retarded in reading and spelling. Dyslexics exhibited a normal right ear advantage on dichotic listening for digits although lesser right ear advantage was related to reading retardation. In the divided visual field task, the normal controls showed a left visual field advantage for digits which it is argued resulted from a failure in fixation linked to reading habits. Within the dyslexic group greater reading deficiency was associated with relative bilateralization for visual verbal processing. The results therefore support the hypothesis.     

Dichotic listening in children: age-related changes in direction and magnitude of ear advantage

Children between the ages of 5 and 12 years were tested with dichotic listening tests utilizing single syllable words and random presentations of digits. They produced a higher prevalence of left ear dominance than expected, especially among right-handed children when tested with words. Whether more children demonstrate the LEA because of right hemisphere dominance for language or because there is less stability in ear advantage direction at younger ages cannot be fully resolved by this study. When ear advantages were measured by subtracting each child's lower score from the higher score without regard to right or left direction, an age-related trend toward lower measures of ear advantage was evident. This trend was greater for dichotic words than for dichotic digits. Structural factors that may be related to these results and possible influences of attention and verbal workload on the two kinds of dichotic stimuli are discussed.     

Is there parallel and independent hemispheric processing of intonational and phonetic components of dichotic speech stimuli?

The possibility of hemisphere interaction in the processing of spoken language was studied in two dichotic listening experiments. The stimulus material consisted of six CV syllable triplets each spoken with each one of six intonation contours. In Experiment I, 15 aphasic patients, 8 patients with unilateral right hemisphere lesions, and 10 normal controls were asked to identify the four components of a dichotic item from a multiple-choice (MC) set comprising all possible CV triplets and intonation contours. In Experiment II, 30 normal subjects were required to identify either the right or left ear stimulus alone from an MC set comprising the right and left ear stimulus together with the two wrong combinations of right ear CV triplet with left ear intonation and vice versa. It is concluded from the results that the left hemisphere is capable of processing both phonetic and intonational information and that there is neither the necessity nor the tendency for right hemisphere participation in the perception of spoken language.     

Consonant-vowel lateralization in dyslexic children: deficit or compensatory development?

Two studies with the same subjects examined dyslexic children's puzzling superiority in forced left ear (LE) dichotic recall with consonant-vowel (CV) combinations. Thirty dysphonemic dyslexics were compared to 30 age-matched and 30 younger reading-matched normal readers. The children were tested in directed attention dichotic listening and in pseudoword decoding, word recognition, reading comprehension, spelling, arithmetic, and general intelligence (IQ). Failure to replicate the LE effect in the first experiment or in free-recall trials suggests its probable origin in aberrant attention/arousal rather than in deviant verbal lateralization. Experiment two replicated the superior LE effect in comparison to both control groups but also found the dyslexics poorer at the right ear (RE). Laterality coefficients confirmed that the dyslexics were more weakly lateralized. Corrections for stimulus dominance revealed that the uncorrected scores (1) concealed the extreme difficulty of the task and (2) obscured floor effects in the LE performance of the normals. Correlations suggest cautiously that CV lateralization may be associated inversely with reading comprehension and word decoding in the dyslexics and normal readers. The results provide mild support for the hypothesis that weak attentional lateralization for CVs in dyslexia may result from the precocious development of posterior right hemisphere attentional systems in compensation for presumed posterior left hemisphere lesions. No support was found for the competing hypothesis that such weak lateralization may be a component of the dyslexics' primary, correlated, or secondary deficit symptomatology.     

The Role of Dichotic Listening Performance and Tasks of Executive Functions in Reading Impairment: A Discriminant Function Analysis

This study focused on the role of dichotic listening performance for the identification of reading impaired subtypes. Dichotic listening (DL), using verbal stimuli, has shown to be a valid measure of language lateralization. Usually, lateralization is estimated from the proportion of right ear over left ear accuracy during a free recall test procedure. However, it has been suggested that a more accurate estimate of laterality can be obtained by using a directed attention procedure. A sample of 43 reading disabled children of whom 18 showed signs of impaired language comprehension skills and 25 without language comprehension impairments, were compared to 20 age, and gender, matched controls on dichotic listening performance in both an unbiased free recall task and in a directed attention task using consonant-vowel syllables as dichotic stimuli. A laterality index was calculated for left and right ear stimuli reported during both the free recall condition and the attended ear-scores for the two directed attention conditions. Although both DL procedures yielded significant group differences, with a lower laterality score for the reading disabled compared to the controls, there was no main effect of DL-procedure or group × procedure interaction. Taken alone, DL performance could correctly classify 42% of the reading impaired samples, but together with other measures of executive functions, discriminant function analyses yielded 90.74% accuracy in classifying reading impaired children. The result indicates that DL together with tests of executive functions are valuable tools for assessment of reading impaired subjects.     

The role of dichotic listening performance and tasks of executive functions in reading impairment: a discriminant function analysis.

This study focused on the role of dichotic listening performance for the identification of reading impaired subtypes. Dichotic listening (DL), using verbal stimuli, has shown to be a valid measure of language lateralization. Usually, lateralization is estimated from the proportion of right ear over left ear accuracy during a free recall test procedure. However, it has been suggested that a more accurate estimate of laterality can be obtained by using a directed attention procedure. A sample of 43 reading disabled children of whom 18 showed signs of impaired language comprehension skills and 25 without language comprehension impairments, were compared to 20 age, and gender, matched controls on dichotic listening performance in both an unbiased free recall task and in a directed attention task using consonant-vowel syllables as dichotic stimuli. A laterality index was calculated for left and right ear stimuli reported during both the free recall condition and the attended ear-scores for the two directed attention conditions. Although both DL procedures yielded significant group differences, with a lower laterality score for the reading disabled compared to the controls, there was no main effect of DL-procedure or group x procedure interaction. Taken alone, DL performance could correctly classify 42% of the reading impaired samples, but together with other measures of executive functions, discriminant function analyses yielded 90.74% accuracy in classifying reading impaired children. The result indicates that DL together with tests of executive functions are valuable tools for assessment of reading impaired subjects.     

Multitask investigation of individual differences in hemispheric asymmetry

Right-handed subjects (N = 120) participated in four different laterality tasks designed to measure aspects of cerebral hemisphere asymmetry: identification of dichotically presented consonant-vowel syllables (CVs), examination of the effects of concurrent repetition of CVs and concurrent anagram solution on finger-tapping by the right and left hands, lateralized identification of CVs presented tachistoscopically to the left and right visual fields, and left/right biases on a free-vision face task involving judgments of emotion. Ear differences in the dichotic listening task were related to the pattern of lateralized interference in the dual-task finger-tapping paradigm. There were no other significant relations between pairs of tasks, but when the present results are considered in the light of other recent experiments, there appears to be a relation between lateral bias on the free-vision face task and visual field differences in tachistoscopic identification. The pattern of results has implications for hypothesized individual differences among right-handers in cerebral dominance for verbal processes, input pathway dominance, and asymmetric arousal of the two cerebral hemispheres.     

汉语普通话声调加工的右耳优势及其机理：一项双耳分听的研究

采用双耳分听的任务探讨了汉语普通话声调加工的右耳优势问题,并引进反应手的因素,探讨了汉语声调加工的右耳优势的机制。结果表明,汉语母语被试对普通话声调的加工存在右耳、左脑优势,但这种优势是相对的,右脑也具备加工声调信息的能力,结果支持了直接通达模型。     

Dichotic testing of cerebral dominance in stutterers

Matched groups of right-handed male stutterers and controls received dichotic presentations of CVs and melodies on two occasions. Right ear advantages were obtained for CVs and left ear advantages for melodies, without significant differences between groups. However, a significantly greater number of stutterers than controls consistently failed to show the expected ear laterality for either type of material.     

Unilateral forced nostril breathing affects dichotic listening for emotional tones

Unilateral forced nostril breathing (UFNB) through the left nostril is associated with enhanced spatial abilities, whereas UFNB through the right nostril is associated with enhanced verbal abilities. However, the effects of UFNB on standard tasks of laterality (e.g., dichotic listening) are unknown. This study employed dichotic listening for word targets, which typically exhibits a right ear advantage (REA), and dichotic listening for emotional targets, which typically exhibits a left ear advantage (LEA). Participants were asked to breathe either through their dominant nostril (congruent UFNB) or to breathe through their non-dominant nostril (incongruent UFNB) for the entire testing session. There was a significant three-way interaction between the type of dichotic listening task, nostril dominance, and nostril assignment, with the expected REA for word targets and the expected LEA for emotional targets-with one exception. Right nostril dominant participants assigned to the congruent condition exhibited an LEA for emotional targets (p < .05). The other three groups exhibited the expected LEA/right hemisphere advantage for the detection of emotional targets and all groups exhibited the expected REA/left hemisphere advantage for detection of word targets. As such, possible bias induced by tactile stimulation of the contralateral face cannot account for these results. Thus, our data are consistent with a selective enhancement of right hemispheric lateralized functions by right nostril UFNB.     

The perception of stress and lateralization of prosody

Three separate dichotic listening tasks were run to determine ear superiority for stress identification. When subjects were asked to identify stress placement in real word minimal stress pairs (hótdog vs. hot dóg), they demonstrated a right ear superiority. When these tokens were filtered so that phonetic and semantic information was eliminated and only the stress pattern remained, a different group of subjects showed a left ear advantage. Finally, with nonsense word counterparts to word stress pairs (bótgog vs. bot góg) preserving phonetic information but lacking semantic content, no ear asymmetry was found. These results suggest that as the linguistic significance of the stimuli is reduced, thereby lessening the linguistic function of stress, there is a less dominant involvement of the left hemisphere in stress processing. Results are discussed in relation to a theory of a functional integration of prosodic and segmental speech components that is paralleled by a working partnership of left and right hemisphere.     

Hemispheric Processing Deficits in Patients with Paranoid Schizophrenia

The purpose of the present study was to investigate hemispheric deficits in individuals with paranoid schizophrenia on four kinds of tasks: dichoptic viewing tasks involving verbal and nonverbal visual stimuli, and dichotic listening tasks involving verbal and nonverbal auditory stimuli. As dependent measures, both accuracy and speed of (correct) responding were measured. The sample recruited for this study consisted of 18 patients with paranoid schizophrenia, 15 outpatients with anxiety disorders, and 20 controls with no history of psychiatric disorders. Results indicated that, relative to the controls, the paranoid schizophrenic patients were less accurate and less efficient on auditory-verbal tasks requiring right hemisphere processing. Unlike the controls, the paranoid schizophrenic patients manifested a lateralized left hemisphere advantage.     

Hemispheric asymmetry and human associative learning: Interactions with attention

In a previous study (Hugdahl & Brobeck, 1986) it was shown that Pavlovian conditioning to an auditory verbal conditioned stimulus (CS) initially presented only to the left cerebral hemisphere was stronger than when the same CS was presented to the right hemisphere. This was followed up in the present study by controlling for the possibility that the effect was caused by laterally biased attention. The study was performed using the “dichotic extinction paradigm,” which consists of three different phases. During the habituation phase, the CS+ and CS- were presented binaurally and separated in time. During the acquisition phase, the CS+ was followed by a white-noise unconditioned stimulus (UCS). During the dichotic extinction phase, the CS+ and CS- were presented dichotically, i.e., simultaneous presentations on each trial. Half of the subjects had the CS+ in the right ear, and half had the CS+ in the left ear. Each group was further divided into two subgroups, with one subgroup instructed to attend only to the right ear input, and the other subgroup to attend only to the left ear input. During acquisition, larger electrodermal responses were obtained to the CS+ than to the CS-. During dichotic extinction, the CS+ right ear group showed superior resistance to extinction compared to the CS+ left ear group, with no effect of the manipulation of attention. The effect was, however, attenuated when levels of acquisition was used as covariates in an analysis of covariance. There were overall larger responses from the left hand recording.     

Hemispheric processing deficits in patients with paranoid schizophrenia

The purpose of the present study was to investigate hemispheric deficits in individuals with paranoid schizophrenia on four kinds of tasks: dichoptic viewing tasks involving verbal and nonverbal visual stimuli, and dichotic listening tasks involving verbal and nonverbal auditory stimuli. As dependent measures, both accuracy and speed of (correct) responding were measured. The sample recruited for this study consisted of 18 patients with paranoid schizophrenia, 15 outpatients with anxiety disorders, and 20 controls with no history of psychiatric disorders. Results indicated that, relative to the controls, the paranoid schizophrenic patients were less accurate and less efficient on auditory-verbal tasks requiring right hemisphere processing. Unlike the controls the paranoid schizophrenic patients manifested a lateralized left hemisphere advantage.     

Dichotic listening with Chinese and English tasks

In this dichotic listening study, monosyllabic tasks were conducted in both English and Chinese to evaluate (1) the effects of processing two acoustically different languages and (2) the effects of bilingualism. One subject group included 28 bilingual speakers of English and Chinese, and a second group in cluded 29 monolingual English speakers. Three pairs of monosyllabic words were presented such that each ear received a different word at the same time. Twenty such sets in both languages were presented, with recall order irrelevant. The results show that the monolingual English subjects demonstrated a significant right ear advantage when identifying English words dichotically, suggesting a left hemisphere processing component. However, there was no ear effect when the English-Chinese speakers performed the dichotic listening tasks in both Chinese and English. It appears that, with the acquisition of a second language, right ear dominance seems to be replaced by interhemispheric processing.I would like to express my deep appreciation to John Ryalls for his efforts in the preparation of this article. Thanks also go to Stuart Davis, Steven Chin, Sven Anderson, David Pisoni, and two anonymous reviewers for their critical comments on previous drafts.     

Dichotic listening during forced-attention in a patient with left hemispherectomy

A young left-handed girl with an extensive posttraumatic lesion in the left hemisphere was tested with dichotic listening (DL) under three different attentional instructions. The major aim of the study was to evaluate a structural vs attentional explanation for dichotic listening. As both her expressive and receptive language functions were intact after the lesion, it was assumed that the right hemisphere was the language-dominant one. In the free-report condition, she was free to divert attention to and to report from both ear inputs. In the forced-right condition, she was instructed to attend to and report only from the right ear input. In the forced-left condition, she was instructed to attend to and to report only from the left-ear input. Her performance was compared with data from a previously collected sample of normal left-handed females. Analysis showed that the patient, in contrast to the normal sample, revealed a complete right-ear extinction phenomenon, irrespective of attentional instruction. Furthermore, she showed superior correct reports from the left ear, compared with those of the normal sample, also irrespective of attentional instruction. It is concluded that these results support a structural, rather than attentional explanation for the right-ear advantage (REA) typically observed in dichotic listening. The utility of validating the dichotic listening technique on patients with brain lesions is discussed.     

Dichotic listening performance in subtypes of developmental dyslexia and a left temporal lobe brain tumor contrast group.

This study examined dichotic listening performance in three subtypes of developmental dyslexia and in children with left temporal lobe brain tumors (clinical contrast group). Each child was administered a free-recall CV syllable dichotic paradigm (30 pairs). Analysis of variance and Tukey-HSD pairwise follow-up comparison indicated that the dichotic listening performance of the left temporal lobe brain tumor contrast group (strong LEA/right ear suppression) was significantly different from those of the visual-spatial/dyseidetic (strong REA/left ear depression) and mixed (moderate REA/bilateral ear suppression) dyslexic subtypes. The language disorder/dysphonetic dyslexic subtype demonstrated a REA with right ear depression. Closer inspection of the individual performances of the language disorder/dysphonetic dyslexic subtype revealed a bimodal distribution with 12 subjects demonstrating a strong LEA/right ear suppression and 8 subjects exhibiting a strong REA/left ear depression. These results lend support for the contention that the dyslexic population is heterogeneous in nature with each subgroup exhibiting (1) a distinct neuropsychological test profile and reading pattern and (2) a pattern of performance on the dichotic listening task which is consistent with what would be expected based upon the pattern of dysfunction exhibited on neuropsychological evaluation.