Cued dichotic listening with right-handed, left-handed, bilingual and learning-disabled children

This study used cued dichotic listening to investigate differences in language lateralization among right-handed (control), left-handed, bilingual, and learning-disabled children. A sample of 60 subjects ranging in age from 7-13 yr were administered a CVC dichotic paradigm with three experimental conditions (free recall, directed left, directed right). A three-factor ANOVA design conducted on the data revealed that control, bilingual, and learning-disabled children produced the expected REA suggestive of left hemisphere dominance for language processing whereas left-handed children produced an LEA suggestive of right hemisphere superiority for language processing. The cued attention data derived from groups as well as from individual subjects suggested that in comparison with control children, left-handed children were greatly susceptible to attentional manipulation similar to learning-disabled children only in the opposite hemisphere. Bilingual children were found to have a REA much like control children although recall accuracy was depressed. Further, lambda (lambda) analyses conducted on individual subjects indicated that the magnitude and degree of perceptual asymmetry varied widely among individuals of various anomaly groups. These findings lend support to the hypothesis that attentional factors play a larger role in unilateral processing for some anomalous groups of children (i.e. left-handers and learning-disabled) while not affecting others (i.e. controls and bilinguals).     

The effects of hemispatial and asymmetrically focused attention on dichotic listening with normal and learning-disabled children

The effects of hemispatial and focused attention were examined with 50 normal and learning-disabled children to determine the extent of these two attentional strategies influenced perceptual laterality as reflected by the dichotic listening right-ear advantage (REA). Twenty-five normal children (8 females, 17 males, mean age 9.10 yr) matched with 25 learning-disabled children (8 females, 17 males, mean age 10.1 yr) were administered a dichotic consonant-vowel (CV) and consonant-vowel-consonant (CVC) syllable task. The two types of stimuli were compared across focused attention (free report, focused left, focused right) and hemispatial (central, left hemispace, right hemispace) conditions implemented independently and in systematic combinations. A four-factorial analysis of variance (groups x stimuli x conditions x ears) resulted in a significant REA for normal children across all attentional conditions whereas learning-disabled did not produce a consistent REA across all attentional conditions, and in several instances, produced equivalent left and right hemisphere processing. Right hemispatial orientation increased the magnitude of the REA (i.e., left hemisphere processing) for both groups, whereas left hemispatial orientation increased the magnitude of the left ear report (i.e., right hemisphere processing) only in learning-disabled subjects. Focused attention to the right ear also increased left hemisphere efficiency for both groups of children; however, focused attention to the left ear produced symmetrical functioning by learning-disabled subjects. Congruent combinations of focused attention and hemispatial orientation were not found to enhance the REA beyond its magnitude when each strategy was assessed independently. When focused attention and hemispatial conditions were employed in opposing directions, normal children were more susceptible to the "rightward" direction regardless of the strategy whereas learning-disabled subjects were more susceptible to the "verbal" nature of the strategy. Higher overall processing performance was exhibited for CVC stimuli when compared to CV stimuli. These findings lend support to the hypothesis that hemispatial and asymmetrically focused attention strategies interact with structural mechanisms in producing the observed REA in dichotic listening and do so differentially for normal and learning-disabled children.     

Verbal dichotic listening in developmental stuttering: subgroups with atypical auditory processing.

OBJECTIVE: The major aim of this study was to determine whether adults with persistent developmental stuttering have atypical auditory processing. BACKGROUND: Stuttering has been attributed to aberrant hemispheric dominance, and auditory processing deficits have been found in some adults who stutter. Dichotic listening, an indirect measure of auditory processing, has not been used to study auditory laterality in right- and left-handers who stutter. Because left-handers and people who stutter may have aberrant hemispheric dominance, it is important to examine auditory neural systems in right- and left-handed people who do and do not stutter. METHODS: Adults with persistent developmental stuttering (n = 18) and matched controls (n = 28) were studied by simultaneous binaural (dichotic) presentation of consonant-vowel stimuli in three attention conditions: nondirected attention, attention directed right, and attention directed left. Sex-handedness groups (stutter and control) included right-handed men and women and left-handed men, but not left-handed women because this stutter subgroup could not be recruited. To study ear advantage and auditory laterality, two dependent measures were examined: percent left and right ear responses and lateralization shift magnitude. Potential relationships between degree of handedness and dichotic listening measures were also examined. RESULTS: Matched controls and right-handed men who stutter had the expected right-ear advantage (REA) in the nondirected attention condition. In contrast, left-handed men who stutter had a left-ear advantage (LEA), and right-handed women who stutter did not have a lateral ear bias in the nondirected attention condition. Right-handed women who stutter had the greatest tendency to hear a sound that was not presented to either ear, and were relatively unable to selectively direct attention left or right. In contrast, left-handed men who stutter were able to shift attention to the left and right ear better than any other group. For the fluent control group, there were no significant relationships among degree of handedness and dichotic-listening variables. For the stutter group, degree of handedness was significantly related to percentage left and right ear response and to the lateralization shift magnitude. CONCLUSIONS: Left-handed men who stutter and right-handed women who stutter have atypical auditory processing but differ in important ways. The left-ear bias found in left-handed men who stutter in the nondirected attention condition suggests that their right temporal lobe may be important in perceiving speech, and, therefore, they have mixed dominance. These subjects were also better at shifting attention in both directions in comparison to all other groups; thus, the right hemisphere, which is dominant for shifting attention to both right and left space, may be activated. In contrast, the right-handed women who stutter had no ear bias in the nondirected attention condition, made more perceptual errors, and had difficulty shifting attention to the left and right. Although these results suggest that right-handed women who stutter have attentional deficits, the relationship between attentional disorders and stuttering remains to be elucidated. Because right-handed men who stutter were not different from controls, aberrant hemispheric dominance cannot fully account for stuttering. Unfortunately, left-handed women were not examined in this study. Therefore, these interesting sex-handedness effects found in left-handed men and right-handed women who stutter must be interpreted with caution.     

Effects of time-of-day on neuropsychological testing as measured by dichotic listening

In a study of 30 reading-disabled and 30 normal-achieving children tested on a dichotic listening task using digits in either morning or afternoon settings neither laterality nor capacity differences were evident between groups in the afternoon. In the morning, the normal-achieving children compared to the disabled readers were more strongly lateralized when attending selectively to the right channel and less lateralized when attending to the left channel, suggesting disabled readers do not respond normally to circadian influences and may suffer from a time-locked dysfunction which reduces their control over attentional resources in the morning. To examine the normal circadian effect further a second study (using 40 normal-achieving, right-handed male children) was conducted using the same dichotic listening stimuli with an order variable included. The increased report in the morning was seen to be linked to a right ear (left hemisphere) priming effect which served to increase the overall report. The effect was evident only for subjects directed to report the right ear first. The results are consistent with a prepotent left hemisphere in the morning which appears to facilitate attending in the morning for subjects directed to attend to their right ear (left hemisphere) first. Potential research and educational implications are discussed.     

Differential effects of awakening from REM and NONREM sleep on dichotic listening performance as a function of handedness

Fourteen right-handed and fourteen left-handed males were wakened from REM and NONREM sleep and tested on the dichotic listening test with verbal stimuli. For right-handers there was a significant right ear advantage (REA) only after REM wakenings, which was equal in magnitude to the REA obtained during waking. Left-handers showed significant REA after both wakening conditions, as well as during waking. These results are interpreted in view of the data suggesting REM-related right hemisphere activation and the role of the right hemisphere in regulating bihemispheric arousal levels.     

The differential hemispheric processing of emotion: a comparative analysis in strongly-lateralized sinistrals and dextrals

The neural processing of emotion and the differential processing of affect and cognition are thus far poorly understood. Complex results across studies suggest involvement of the left hemisphere, the right hemisphere, or both. Since handedness is related to cerebral dominance, the present study undertook a comparative analysis of neural processing in strongly lateralized left- and right-handed populations. Parietal EEG and bilateral electrodermal activity were recorded while carefully selected subjects were exposed to emotional stimuli under cognitive, affective, and neutral conditions. Results showed greater lateral differentiation and differentially greater left-hemisphere activation in dextrals but greater overall activation in sinistrals. These findings are consistent with the common observation that cerebral organization is more diffuse in left-handed populations. It seems clear that the comparative study of sinistrals and dextrals can help us to better understand how emotion is processed in the brain.     

Verbal dichotic listening in right and left-handed adults: laterality effects of directed attention

Dichotic listening performance of consonant vowel stimuli was studied in 51 adult right- and left-handers in three attention conditions: non-directed and directed to either the right or left ear. In the non-directed condition, a significant right-ear advantage was found in both handedness groups with a stronger asymmetry in right-handers. There are at least three explanations for this ear bias. The classic or structural hypothesis suggests that to the right ear projects more strongly to the language dominant left hemisphere. The callosal relay hypothesis is based on the influence of inhibitory connections via the corpus callosum. The attentional hypothesis suggests that each hemisphere primarily directs attention to contralateral space and because the left hemisphere is dominant for language in both groups, and is aroused by speech stimuli, attention is primarily directed to the right ear. Neither hypothesis can explain why greater than 95% of right-handers have left hemisphere language dominance, but only 70-80% have a right ear bias. Our results demonstrate that in the directed attention conditions both groups increased their lateral biases when directed to either the right or left. The classic or structural hypothesis cannot account for these changes, thereby providing support for the attentional hypothesis. In addition, the right-handed subjects exhibited a greater shift of bias than did the left-handed subjects, when directing their attention leftward. This finding suggests that right-handed people are better able to shift their attention than left-handed people.     

Absence of Ear advantage on the consonant-vowel dichotic listening test in adolescent and adult dyslexics: Specific auditory-phonetic dysfunction

Abstract

The present study investigated auditory-phonetic processing in a group of adolescent and adult reading disabled subjects. Right- and left-handed dyslexic subjects were compared with an age, sex, and handedness matched control group. All subjects were studied with a consonant-vowel version of the dichotic listening task with repeated presentations of dichotically presented pairs of CV-syllables. Left and right ear correct scores were compared for ear advantage in each of the different subgroups of subjects. The main finding was the absence of an expected right-ear advantage (REA) in the right-handed dyslexic group as compared to the right-handed normal readers. Both the dyslexic and normal left-handed groups did not show a REA. The findings are discussed within a theoretical framework that focuses on a basic auditoryphonetic processing dysfunction in developmental dyslexia that persists into adulthood.     

Pathological left-handedness revisited: dichotic listening in children with left vs right congenital hemiplegia.

Thirty-one children with right (n = 18) and left (n = 13) congenital hemiplegia were compared for incidence of hand- and foot-preference, eye-dominance, and familial sinistrality. In addition, they were tested with dichotic listening for correct reports of consonant-vowel syllables. The two groups of children were closely matched on IQ and sensory functioning. Children with mental retardation, or epileptic seizures were not included. The results showed that 89% of the left hemisphere impaired (LHI) children were left-handed, all of them preferred the left foot, and 72% were left eye-dominant. In the right hemisphere impaired (RHI) group, everyone (100%) preferred the right hand and foot, and 62% were right eye dominant. The dichotic listening results showed a significant right ear advantage (REA) in the RHI-group, and a significant left ear advantage (LEA) in the LHI-group. The results are discussed in the framework of pathological handedness and shifts in hemisphere control of language in children with early brain injury. It is argued that the homogeneous samples, except for the site of lesion, provides an interesting possibility to compare cognitive effects of left and right hemisphere impairment in children.     

Priming inhibits the right ear advantage in dichotic listening: implications for auditory laterality

The typical finding in dichotic listening with verbal stimuli is the right ear advantage (REA), indicating a left hemisphere processing superiority, thus making this an effective tool in studying hemispheric asymmetry. It has been shown that the amplitude of the REA can be modulated by instructions to direct attention to left or right side. The current study attempted to modulate the REA by changing the dichotic listening stimulus situation. In Experiment 1, a consonant vowel (CV) syllable prime was presented binaurally briefly before the dichotic stimuli (consisting of two CVs). The prime could be the same as either the left or right ear dichotic stimulus, or it could be a different stimulus. Participants were instructed to report the CV they heard best from the dichotic syllable pair. The traditional REA was found when the prime was different from both dichotic stimuli. When the prime matched the CV in the left half of the subsequent dichotic pair, the REA was increased, while if the prime matched the right half, the REA was reduced. In order to see at which perceptual stage the modulation takes place, in Experiment 2 the prime was visual, presented on a PC screen. The same effect was seen, although the modulation of the REA was weaker. We propose that the memory trace of the prime is a source of interference, and causes cognitive control of attention to inhibit recognition of stimuli similar to recent distractors. Based on previous studies we propose that this inhibition of attention is performed by prefrontal cortical areas. Similarities to the mechanisms involved in negative priming and implications for auditory laterality studies are pointed out.     

Dichotic listening performance suggests right hemisphere involvement in PTSD

The present study focuses on language laterality as measured with dichotic listening (DL) to consonant-vowel syllables (CV syllables) in refugees with post-traumatic stress disorder (PTSD). PTSD is associated with impaired callosal transfer and with increased right hemisphere activation and impaired executive skills that could influence the processing of dichotic stimuli. A total of 22 participants with PTSD were compared to 23 participants without a diagnosis of PTSD. All participants had similar experiences of acts of war and political violence. They were tested with dichotic listening to CV syllables with free recall and directed attention following the forced attention paradigm. The PTSD group showed increased right ear advantage due to impaired left ear reporting and also smaller attention modulation compared to the control group, and the performance shared variance with self-report measures of arousal and intrusive memories. The results are discussed towards a model of impaired functionality of the frontal lobe and right hemisphere versus impaired callosal transfer, both yielding predictions for the processing of the left ear input and the ability to attention modulation of the performance.     

Dichotic listening performance suggests right hemisphere involvement in PTSD

The present study focuses on language laterality as measured with dichotic listening (DL) to consonant-vowel syllables (CV syllables) in refugees with post-traumatic stress disorder (PTSD). PTSD is associated with impaired callosal transfer and with increased right hemisphere activation and impaired executive skills that could influence the processing of dichotic stimuli. A total of 22 participants with PTSD were compared to 23 participants without a diagnosis of PTSD. All participants had similar experiences of acts of war and political violence. They were tested with dichotic listening to CV syllables with free recall and directed attention following the forced attention paradigm. The PTSD group showed increased right ear advantage due to impaired left ear reporting and also smaller attention modulation compared to the control group, and the performance shared variance with self-report measures of arousal and intrusive memories. The results are discussed towards a model of impaired functionality of the frontal lobe and right hemisphere versus impaired callosal transfer, both yielding predictions for the processing of the left ear input and the ability to attention modulation of the performance.     

Parallel processing of verbal and musical stimuli in right and left hemispheres

Parallel processing of verbal and tonal material was studied in sixteen trained musicians, who under simple dichotic conditions had right ear superiority for verbal and left ear superiority for tonal stimuli. Concurrent processing was induced by presenting spoken numbers superimposed on piano notes in each ear and, in another condition, by presenting competing digits sung to competing tonal patterns. Independent right ear superiority for the verbal component and left ear superiority for the tonal component of each stimulus was maintained under all conditions. It is concluded that the two hemisphere concurrently and independently process that component of a complex stimulus for which each is dominant.     

An exploration of dichotic listening among adults who stutter

Abstract

A pilot investigation of dichotic listening of CV stimuli was undertaken using seven adults who stutter (AWS) and a comparison group of seven adults who do not stutter (AWNS). The aim of this research was to investigate whether AWS show a difference in the strength of the right ear advantage (REA) in both undirected and directed attention tasks when compared to AWNS. The undirected attention task involved manipulating the interaural intensity difference (IID) of the CV stimuli presented to each ear. The CV stimuli were presented with equal intensity for the directed attention task. The undirected attention results indicated that both AWS and AWNS have a REA for processing speech information, with a primary difference observed between groups in regard to the IID point at which a REA shifts to a LEA. This crossing-over point occurred earlier for AWS, indicating a stronger right hemisphere involvement for the processing of speech compared to AWNS. No differences were found between groups in the directed attention task. The differences and similarities observed in dichotic listening between the two groups are discussed in regard to hemispheric specialization in the processing of speech.     

The influence of musical experience on lateralisation of auditory processing

The influence of musical experience on free-recall dichotic listening to environmental sounds, two-tone sequences, and consonant-vowel (CV) syllables was investigated. A total of 60 healthy right-handed participants were divided into two groups according to their active musical competence ("musicians" and "non-musicians"). In both groups, we found a left ear advantage (LEA) for nonverbal stimuli (environmental sounds and two-tone sequences) and a right ear advantage (REA) for CV syllables. Dichotic listening to environmental sounds was uninfluenced by musical experience. The total accuracy of recall for two-tone sequences was higher in musicians than in non-musicians but the lateralisation was similar in both groups. For CV syllables a lower REA was found in male but not female musicians in comparison to non-musicians. The results indicate a specific sex-dependent effect of musical experience on lateralisation of phonological auditory processing.     

The relationship between right-handed children's assessed and familial handedness and lateral specialization

Eighty right-handed males (6–12 yr of age) stratified into age x degree of handedness x family history of handedness groups were administered three dichotic (digit, syllable, environmental sound) tests. Older subjects accurately identified more stimuli than the younger subjects across tasks. There were significant laterality differences for both verbal and nonverbal stimuli between family history of handedness groups regardless of the subjects' age and degree of handedness. Those subjects with familial sinistrality had attenuated right-side advantage for verbal and non-verbal stimuli and decreased nonverbal accuracy scores compared to the familial dextral subjects who evidenced a right-ear (left hemisphere) advantage for verbal stimuli and a left-ear (right hemisphere) advantage for nonverbal.     

The "forced-attention paradigm" in dichotic listening to CV-syllables: a comparison between adults and children

The present study was concerned with the effects of directional attention on the right-ear-advantage (REA) in dichotic listening. It was suggested that if selective attention contributes to the REA during a non-forced, free recall condition, then comparing the unattended left and right ear scores when attention is forced to the right and the left ear, respectively, would yield an "attention-free" estimate of the REA. Each subject participated in a non-forced, free recall, condition; in a forced-right condition; and in a forced-left condition. During the two forced conditions, subjects were instructed to only attend to and report the right and left ear inputs, respectively. The stimuli were the six stop-consonants paired with the vowel a. Four right-handed groups participated (N = 18): Adult males, adult females, boys (8-9 years), girls (8-9 years). The results showed a significant REA in all groups during the non-forced condition. During the forced-right condition, significantly more correct recalls were obtained from the right compared to the left ear in all groups. During the forced-left condition, significantly more correct recalls from the left compared to the right ear was obtained only in the two adult groups, but not in the children groups. Finally, comparing correct recalls from the unattended right ear (during the forced-left condition) with the unattended left ear (during the forced-right condition) revealed a significant REA in all groups except for the adult females.     

Dichotic listening: what does it measure?

Auditory lateralization was investigated in 26 right-handed and 26 left-handed, normal subjects using seven different dichotic listening tests in each proband (free recall of digit lists, free recall of consonant-vowel (CV) syllables, four different CV syllable monitoring paradigms, and free recall of Morse codes). Reliabilities calculated with the formula of Spearman-Brown were low for digit recall (0.29, corrected for test length: 0.50), but good for CV recall (0.83), CV monitoring (0.75-0.88), and Morse code recall (0.50, corrected for test length: 0.88). Nevertheless, interest correlations were low, both for right- and left-handers (negative correlations ranging from -0.44 to -0.05, positive correlations ranging from 0.01 to 0.51). Only 38-77% of the right-handed and left-handed subjects retained one direction of ear advantage across any combination of two tests. The data suggest that different dichotic tests reveal different results. This may be due to psychometric, procedural, or phonetic properties. We conclude that individual predictions of language dominance are not justified using the dichotic tests evaluated in the present study.     

Hemispheric asymmetry in processing visual half-field pattern-reversal stimuli assessed by reaction time and evoked potentials

Reversing checkerboard patterns, like those used to elicit clinical visual evoked potentials (VEPs), were adapted to the study of cerebral lateralization of visual processing in a divided visual field experiment. Seventeen right-handed subjects (9 male, 8 female) provided left- and right-handed responses to pattern-reversal stimuli presented in left, right and both visual half-fields in pseudorandom order. Simple unwarned RTs were shorter for left- compared with right-field stimuli under left-hand response conditions. Parietal VEPs obtained from 9 of the subjects showed larger amplitudes for left compared with right field stimuli at the right hemisphere. The results were consistent with an efficiency model of cerebral dominance incorporating both interhemispheric transfer time and a reduced efficiency for left hemisphere processing of our patterned visual stimuli.     

Cerebral lateralization and cognitive deficits after congenital hemiparesis

The purpose of this study was to investigate whether and how handedness is related to the processes of cerebral lateralization and cognitive performance in children with congenital insult. Fifty-six children (31 males and 25 females) with congenital hemiparesis and 14 control subjects were investigated. Of these children, 32 had a left hemisphere lesion, and 24 children had a right hemisphere lesion. There were 30 right-handed, 23 left-handed, and three ambidextrous children in the study group. The neuropsychologic assessment was performed using the NEPSY (a developmental neuropsychological assessment of child development) test battery. We found that 41% of the hemiparetic children and 72% of the children with a left hemisphere lesion were left-handed. In children contralateral to lesion handedness (no evidence of interhemispheric transfer of functions), we found diffuse cognitive deficits with impaired language abilities and poor visuomotor and narrative memory processing. In contrast, children with ipsilateral to brain lesion handedness (interhemispheric transfer of functions) demonstrated minimal or moderate side-specific cognitive dysfunction. Right-handed children with a right hemisphere lesion had attention, spatial, and short-term memory problems; left-handed children with a left hemisphere lesion had receptive language and visuomotor difficulties. Handedness combined with neuropsychologic assessment is a reliable indicator of the processes of cerebral reorganization after early brain insult.