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.     

Dichotic listening studies of hemispheric asymmetry in brain damaged patients.

In the present paper we review the empirical evidence for structural versus attentional explanations of the right ear advantage (REA) phenomenon in dichotic listening (DL). The ear advantage in DL is a behavioral "marker" of language function in the cerebral hemispheres. Dichotic listening data from four brain-lesioned patients are presented. The patients had a tumor or cyst in the left Sylvian region (2 cases); hemorrhage in the left frontotemporal region (1 case); and severe destruction of the left hemisphere (1 case). The results from all four patients showed marked reductions in correct recall of the right ear items, while left ear recall was left unaffected. In two of the cases, the DL data showed an immediate reinstatement of the REA after neurosurgery. It is concluded that the results favor a structural/anatomical explanation of the ear advantage phenomenon in DL, rather than an attentional bias explanation.     

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.     

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.     

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.     

Schizophrenia subgroups differing in dichotic listening laterality also differ in neurometabolism and symptomatology

Schizophrenia patients vary in right ear advantage (REA) on dichotic listening tests for assessing left hemispheric dominance for language processing. The authors examined if patients with low REA differed from other patients in symptoms and in resting brain metabolism. SPECT was conducted during visual fixation for 9 healthy control subjects and 16 schizophrenia patients: 8 with normal and 8 with diminished REA. REA-diminished patients had greater positive symptoms and lower mental status scores (all P<0.05) and had right middle temporal gyrus hypermetabolism. Both schizophrenia groups had decreased right frontal and increased medial temporal lobe metabolism vs. control subjects. REA-diminished patients had right temporal lobe hypermetabolism under a resting condition (eyes open, visual fixation). Results suggest reduced right ear (left hemisphere) advantage for dichotic word perception in schizophrenia is related to a predisposition to overactivate right temporal lobe regions and to positive symptoms. In contrast, the prefrontal-medial temporal imbalance present in both patient groups may typify the schizophrenia syndrome.     

Dichotic target detection with words: a modified procedure

The purpose of the present study was to investigate the influence of attention on the magnitude and reliability of laterality effects in dichotic target detection. Twenty-five participants completed a dichotic target detection task requiring them to identify the ear to which a target word was presented. Correct left and right responses (LL and RR outcomes, respectively) produced a large and reliable right ear advantage (REA). Participants circled right when the target was presented to the left ear (LR outcomes) more often than they circled left when the target was presented to the right (RL outcomes). A combination of the LL+LR outcomes compared to RR+RL outcomes resulted in a reduced REA. Finally, cases where participants incorrectly responded left or right when the target was absent produced no systematic differences, reflecting the absence of a generalized bias to respond "right." The discussion emphasizes the usefulness of the approach presented here in producing a score that minimizes the attentional component of laterality effects.     

Side of the stimulated ear influences the hemispheric balance in coding tonal stimuli

OBJECTIVE: To evaluate whether the side of stimulated ear affects the hemispheric asymmetry of auditory evoked cortical activations. METHODS: Using a whole-head neuromagnetometer, we recorded neuromagnetic approximately 100 ms responses (N100m) in 21 healthy right-handers to 100 ms 1 kHz tones delivered alternatively to left and right ear. RESULTS: Although the peak latencies of N100m were shorter in contralateral than in ipsilateral hemisphere, the difference was significant only for the left ear stimulation. Based on the relative N100m amplitudes across hemispheres, the laterality evaluation showed a rightward predominance of N100m activation to tone stimuli, but the lateralization toward the right hemisphere was more apparent by the left than by the right ear stimulation (laterality index: -0.27 versus -0.10, p=0.008). Within the right hemisphere, the N100m was 2-4 mm more posterior for left ear than for right ear stimulation. CONCLUSIONS: The hemispheric asymmetry in auditory processing depends on the side of the stimulated ear. The more anterior localization of right N100m responses to ipsilateral than to contralateral ear stimulation suggests that there might be differential neuronal populations in the right hemisphere for processing spatially different auditory inputs.     

Laterality of basic auditory perception

Laterality (left-right ear differences) of auditory processing was assessed using basic auditory skills: (1) gap detection, (2) frequency discrimination, and (3) intensity discrimination. Stimuli included tones (500, 1000, and 4000 Hz) and wide-band noise presented monaurally to each ear of typical adult listeners. The hypothesis tested was that processing of tonal stimuli would be enhanced by left ear (LE) stimulation and noise by right ear (RE) presentations. To investigate the limits of laterality by (1) spectral width, a narrow-band noise (NBN) of 450-Hz bandwidth was evaluated using intensity discrimination, and (2) stimulus duration, 200, 500, and 1000 ms duration tones were evaluated using frequency discrimination. A left ear advantage (LEA) was demonstrated with tonal stimuli in all experiments, but an expected REA for noise stimuli was not found. The NBN stimulus demonstrated no LEA and was characterised as a noise. No change in laterality was found with changes in stimulus durations. The LEA for tonal stimuli is felt to be due to more direct connections between the left ear and the right auditory cortex, which has been shown to be primary for spectral analysis and tonal processing. The lack of a REA for noise stimuli is unexplained. Sex differences in laterality for noise stimuli were noted but were not statistically significant. This study did establish a subtle but clear pattern of LEA for processing of tonal stimuli.     

Do Individuals with Down's Syndrome Possess Right Hemisphere Language Dominance?

A dichotic digits task with selective listening and attention-switching instructions, was administered to 10 mentally retarded individuals with Down's Syndrome between the ages of 10 and 37 years. Attention was focused on one ear for 20 trials before switching attention to the opposite ear after a 5-minute interval. A majority displayed a right ear-left hemisphere advantage for correct responses, although this advantage failed to reach significance. Comparison of left and right ear intrusion errors when each ear was attended first showed significantly more intrusions from the unattended right ear. No priming effects were found. The results do not support the hemispheric reversed specialization hypothesis. Rather, it is suggested that while Down's Syndrome individuals do possess an inherent left hemisphere advantage for language, such individuals may suffer from a left hemisphere information processing disorder that can produce functional reversals in dichotic listening.     

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.     

Verbal and nonverbal auditory processing among left- and right-handed good readers and reading-disabled children

Cerebral lateralization of left- and right-handed good readers and left- and right-handed reading disabled was examined with a sample of 60 children who ranged in age from 7-13 years via a dichotic selective attention task (free recall, directed left, directed right) using consonant-vowel (CV) and tonal stimuli. Several ANOVAs were conducted to evaluate gender, reader group, handedness, and stimuli effects of left- and right-ear reports across dichotic conditions. Results indicated males outperformed females across stimuli and conditions regardless of handedness and all subjects recalled more tonal stimuli than CV stimuli. More importantly, the expected REA (left hemisphere processing) was found for CV stimuli only by right-handed good readers across all three dichotic conditions. The left-handed good readers and left-handed reading-disabled children were left ear (LE) dominant in free recall and in the directed left condition, but were right ear (RE) dominant in the directed right condition. Conversely, right-handed reading-disabled children produced a REA during free recall and directed right conditions, but were LE dominant in the directed left condition. In contrast, a significant LEA (right hemisphere processing) was found for tonal stimuli across all dichotic conditions for all four groups. These findings lend support to the hypothesis that attentional factors have a greater influence on auditory processing of verbal than nonverbal stimuli for various groups of children and also suggest reversed or bilateralized processing abilities for language in strongly left-handed children with sinistral relatives.     

Brainstem evoked potentials in learning disabled children

Averaged brainstem auditory responses (BAER) were recorded using left and right ear stimulation with clicks of 90 dBs in two groups of primary school children (control and learning disabled). A linear multiple regression model was used in an attempt to demonstrate the effects of sex, high risk factors related to brain damage and learning disability on the evoked responses. Sex showed a strong influence in the latencies of the first five peaks, with girls having shorter latencies. Risk factors had an effect on the latency of peak V, the I-V interval and the V/I amplitude ration, but only when the left ear was stimulated. Learning disability had no significant influence according to this analysis. Multivariate test of complete homogeneity showed highly significant differences between LD and control boys when the left ear was stimulated and between control and LD girls when the right ear was stimulated. Principal component analyses revealed differences between the two groups: the BAER components of the control subjects showed a minor source of variance when the right ear was stimulated. A contrary effect was observed in LD children. Such differences might be related to ear preference and hemispheric dominance.     

Left ear advantages in detecting emotional tones using dichotic listening task in an Arabic sample

Advantages associated with the left ear (right brain hemisphere) have been reported in some studies. Of these, some have specifically suggested that the left ear has a more heightened ability to detect emotional tones. Meanwhile others have pointed to factors such as age and gender as potentially leading to manifestations of human laterality. This study investigates which brain hemisphere is more involved in emotional processing of auditory information in Arab participants. We aimed to replicate the previous studies because no single study has been done in the Arabic region previously. Additionally, people in this region prefer to use the right side of their body, e.g., hand, ear, foot, etc., for most daily tasks. To acquire data a dichotic listening task (DLT) was administered to 28 male and 23 female (Edinburgh, UK) university students aged 19 to 38; 13 were left-handed and 38 were right-handed. The results showed a significant left ear advantage in the auditory processing of emotional information. There was a significant negative correlation between ear preference and handedness. Left ear advantage related only to handedness. Thus right-handed participants were more likely than left-handers to have a left ear advantage. The relationship between ear preference and gender was non-significant. The conclusion that might be drawn from this study is that the left ear (right hemisphere) is more involved in emotional processing than the right ear (left hemisphere), especially for right-handed people.     

Auditory discrimination of voice-onset time and its relationship with reading ability

The perception of voice-onset time (VOT) during dichotic listening provides unique insight regarding auditory discrimination processes and, as such, an opportunity to learn more about individual differences in reading ability. We analysed the responses elicited by four VOT conditions: short–long pairs (SL), where a syllable with a short VOT was presented to the left ear and a syllable with a long VOT was presented to the right ear, as well as long–short (LS), short–short (SS), and long–long (LL) pairs. Stimuli were presented in three attention conditions, where participants were instructed to attend to either the left or right ear, or received no instruction. By around 9.5 years of age children perform similarly to adults in terms of the size and relative magnitude of the right ear advantage (REA) elicited by each of the four VOT conditions. Overall, SL pairs elicited the largest REA and LS pairs elicited a left ear advantage (LEA), reflecting stimulus-driven bottom-up processes. However, children were less able to modulate their responses according to attention condition, reflecting a lack of top-down control. Effective direction of attention to one ear or the other was related to measures of reading accuracy and comprehension, indicating that reading skill is associated with top-down control of bottom-up perceptual processes.     

Dichotic listening in 126 left-handed children: ear advantages, familial sinistrality and sex differences

In the present study we report data on dichotic listening (DL) performance in 126 left-handed children. Four specific questions were addressed: (1) What is the percentage of left-handers in a large sample of children in Sweden? (2) What is the distribution of children showing a right ear (REA), left ear (LEA), and no ear (NEA) advantage in DL? (3) What is the relationship between ear advantage and familial sinistrality in children? (4) Are there sex differences among left-handed children, and if so, are these differences also reflected in DL performance? The results showed that the left-handers constituted 8.1% of the total sample of the screened subjects. The DL results showed 65.0% REA, 25.4% LEA, and 9.6% NEA. Of the subjects, 45.2% had left-handed relatives. Overall, there were more boys than girls in the sample (65.1% vs 34.9%). It is concluded that the present data match the sodium-Amytal data on left-handed adults with about 2/3 of a left-handed population with left hemisphere language dominance.     

Emotional language is all right: Emotional prosody reduces hemispheric asymmetry for linguistic processing

ABSTRACT

In an influential paper, Bryden and MacRae [(1989). Dichotic laterality effects obtained with emotional words. Neuropsychiatry, Neuropsychology, and Behavioral Neurology, 1, 171–176] introduced a dichotic listening task that allowed for the assessment of linguistic and prosodic processing asymmetries using the same stimuli. The task produces a robust right ear advantage (REA) for linguistic processing (identifying a target word), and a left ear advantage for emotional processing (identifying a target prosody). Here, we adapted this paradigm to determine whether and how the presence of emotional prosody might modulate hemispheric asymmetry for linguistic processing. Participants monitored for a target word among dichotic stimuli consisting of two different words, but spoken in the same emotional prosody—neutral, angry, happy, sad, or fearful. A strong REA was observed when the words were spoken in neutral prosody, which was attenuated for all the emotional prosodies. There were no differences in the ear advantage as a function of valence or discrete emotion, indicating that all emotions had similar effects. Findings are consistent with the hypothesis that the right hemisphere is better able to process speech when it carries emotional prosody. Implications for understanding of right hemisphere language functions are discussed.     

Laterality in the perception of temporal cues of musical timbre

Laterality in the perception of non-stationary aspects of musical timbre was investigated in 54 right-handed non-musicians. Timbre differences were produced by altering the amplitude envelope of a steady-state complex tone. Two single-choice tests with attention directed to one ear were used—a dichotic test and a monaural test with contralateral white noise. Dependent variables were reaction time and accuracy. Both tests showed a significant left ear advantage for reaction time. For the accuracy variable, a significant left ear advantage was found only in the monaural test. Results are briefly discussed in terms of their compatibility with the generally accepted notion that spectral and temporal integrations of sounds are primarily functions of the right and left hemisphere, respectively.     

Hemisphere priming through practice in a musical chords task

In a study of selective hemisphere activation, the performance of 30 subjects given either a "local" or "global" priming activity before and after a monoaurally presented chord analysis task was compared with an unprimed control group. The hypothesis was that ear advantage scores on the chords task would show increased left hemisphere involvement following local priming and increased right hemisphere involvement following global priming. The results failed to support this hypothesis. All subjects, however, regardless of priming condition, showed a very strong practice effect represented by a shift from a weak initial left ear (right hemisphere) advantage towards a significant right ear (left hemisphere) advantage (P less than 0.00006). The findings suggest that although the local/global priming activity did not lead to selective hemisphere activation, repeated exposure to the chords task resulted in increased use of analytic left hemisphere processing strategies as subjects became familiar with its processing requirements.     

Left hemisphere dysfunction affects dichotic listening in patients with temporal lobe epilepsy

This study evaluated the relative effect of left hemisphere dysfunction and side of seizure onset on dichotic listening performance in patients with temporal lobe epilepsy and left hemisphere speech dominance. Seventeen patients were divided into groups based on side of seizure onset and based on scores on a composite measure revealing left hemisphere dysfunction. The group with left hemisphere dysfunction had more correct responses from the left ear, and a left ear advantage, on dichotic listening. The group with normal left hemisphere function showed the expected right ear advantage. Side of seizure onset did not affect dichotic listening performance significantly.