Extinction of auditory stimuli in hemineglect: Space versus ear

Unilateral extinction of auditory stimuli, a key feature of the neglect syndrome, was investigated in 15 patients with right (11), left (3) or bilateral (1) hemispheric lesions using a verbal dichotic condition, in which each ear received simultaneously one word, and a interaural-time-difference (ITD) diotic condition, in which both ears received both words lateralised by means of ITD. Additional investigations included sound localisation, visuo-spatial attention and general cognitive status. Five patients presented a significant asymmetry in the ITD diotic test, due to a decrease of left hemispace reporting but no asymmetry was found in dichotic listening. Six other patients presented a significant asymmetry in the dichotic test due to a significant decrease of left or right ear reporting, but no asymmetry in diotic listening. Ten of the above patients presented mild to severe deficits in sound localisation and eight signs of visuo-spatial neglect (three with selective asymmetry in the diotic and five in the dichotic task). Four other patients presented a significant asymmetry in both the diotic and dichotic listening tasks. Three of them presented moderate deficits in localisation and all four moderate visuo-spatial neglect. Thus, extinction for left ear and left hemispace can double dissociate, suggesting distinct underlying neural processes. Furthermore, the co-occurrence with sound localisation disturbance and with visuo-spatial hemineglect speaks in favour of the involvement of multisensory attentional representations.     

The dynamic nature of language lateralization: effects of lexical and prosodic factors

In dichotic listening, a right ear advantage for linguistic tasks reflects left hemisphere specialization, and a left ear advantage for prosodic tasks reflects right hemisphere specialization. Three experiments used a response hand manipulation with a dichotic listening task to distinguish between direct access (relative specialization) and callosal relay (absolute specialization) explanations of perceptual asymmetries for linguistic and prosodic processing. Experiment 1 found evidence for direct access in linguistic processing and callosal relay in prosodic processing. Direct access for linguistic processing was found to depend on lexical status (Experiment 2) and affective prosody (Experiment 3). Results are interpreted in terms of a dynamic model of hemispheric specialization in which right hemisphere contributions to linguistic processing emerge when stimuli are words, and when they are spoken with affective prosody.     

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.     

Atypical brain laterality in adults with ADHD during dichotic listening for emotional intonation and words

Few studies directly examined the nature of hemispheric specialization and interaction in ADHD. The present experiment investigated left/right brain dynamics in unmedicated right handed adults with ADHD (n = 19) and in controls (n = 19), using a dichotic listening task to assess hemispheric differences in word and emotion recognition. We also assessed how focusing attention on a single ear modulated lateralized performance and affected cross-callosal interference effects. Analysis of variance indicated that ADHD subjects showed reduced left hemisphere specialization, were better at processing emotions, and worse at processing words compared to controls. These differences were eliminated during focused attention. Finally, during presumed right hemisphere processing of linguistic stimuli, subjects with ADHD showed reduced left hemisphere interference. We concluded that ADHD subjects demonstrated greater right hemisphere and reduced left hemisphere contribution during this task relative to controls. We posit that these hemispheric differences were due to management or use of available cognitive resources rather than inherent capacity.     

Speech lateralization and attention/executive functions in a Finnish family with specific language impairment (SLI)

Hemisphere lateralization for speech perception was investigated in a Finnish family with specific language impairment. We used dichotic presentations of consonant-vowel (CV) syllables, consisting of the six stop-consonants paired with the vowel /a/, under three different attentional instructions. The dichotic listening technique means that two different speech stimuli are presented simultaneously, one in each ear. Left hemisphere dominance for speech perception is assessed from a preference for the right ear stimulus. Response accuracy was compared in five members, over three generations, of a family with SLI with 5 healthy control subjects. The dichotic listening task was performed under three different instructions, to attend only to the right ear stimulus, to attend only to the left ear stimulus, or with no instruction about attention. The subjects indicated orally which of the six CV-syllables they heard on each trial. There were 36 dichotic presentations of the CV-syllables for each instruction. The CV-syllables were played from a CD with digitized stimuli. The results showed no difference between the groups during the no instruction condition, indicating normal speech lateralization in the SLI group. However, the SLI group was deficient in modifying the ear advantage through focused attention to the left ear, thus indicating an attentional/executive deficit in addition to a deficit in left hemisphere lateralization. It is concluded that individuals with specific language impairment may have a cognitive deficit related to attention in addition to a language processing deficit related to left hemisphere function.     

Normative Data for Equivalent,Parallel Forms of the Judgment of Line Orientation test

Hemisphere lateralization for speech perception was investigated in a Finnish family with specific language impairment. We used dichotic presentations of consonant–vowel (CV) syllables, consisting of the six stop-consonants paired with the vowel /a/, under three different attentional instructions. The dichotic listening technique means that two different speech stimuli are presented simultaneously, one in each ear. Left hemisphere dominance for speech perception is assessed from a preference for the right ear stimulus. Response accuracy was compared in five members, over three generations, of a family with SLI with 5 healthy control subjects. The dichotic listening task was performed under three different instructions, to attend only to the right ear stimulus, to attend only to the left ear stimulus, or with no instruction about attention. The subjects indicated orally which of the six CV-syllables they heard on each trial. There were 36 dichotic presentations of the CV-syllables for each instruction. The CV-syllables were played from a CD with digitized stimuli. The results showed no difference between the groups during the no instruction condition, indicating normal speech lateralization in the SLI group. However, the SLI group was deficient in modifying the ear advantage through focused attention to the left ear, thus indicating an attentional/executive deficit in addition to a deficit in left hemisphere lateralization. It is concluded that individuals with specific language impairment may have a cognitive deficit related to attention in addition to a language processing deficit related to left hemisphere function.     

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.     

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.     

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.     

Blind individuals show enhanced perceptual and attentional sensitivity for identification of speech sounds

We report on enhanced processing of speech sounds in congenitally and early blind individuals compared with normally seeing individuals. Two different consonant-vowel (CV) syllables were presented via headphones on each presentation. We used a dichotic listening (DL) procedure with pairwise presentations of CV syllables. The typical finding in this paradigm is a right ear advantage, indicating better processing of the CV-syllable stimuli in the left hemisphere. The dichotic listening procedure involved three different conditions, with instructions to pay attention to the right ear stimulus, the left ear stimulus or no specific instruction. The participants were 14 congenitally or early blind Finnish-speaking individuals that were compared with 129 normal seeing Finnish-speaking individuals. The blind participants reported overall significantly more correct syllables than seeing control subjects. When instructed to pay attention to the left ear stimulus and only report from the attended channel, they were again significantly better than the seeing control subjects. These findings indicate effects of hemispheric reorganization in blind individuals at both the sensory and cognitive levels of information processing in the auditory sensory modality.     

Interaction between handedness and the attentional bias during tests of dichotic listening performance

Abstract

Perceptual advantages are typically interpreted as direct expressions of underlying hemispheric functional asymmetries. However, many other confounding factors including the asymmetric distribution of attention may also contribute to either the magnitude or direction of any of these advantages. In a series of experiments, Mondor and Bryden (1991, 1992a, 1992b) found that right-handed subjects bias their attention toward the right ear when faced with a difficult dichotic listening task. The present study was undertaken to determine whether the direction of the attentional bias is associated with handedness. The focus of auditory spatial attention was manipulated in a dichotic listening paradigm by presenting a pretrial tone cue to the ear from which the subject was required to report. The time period between the onset of the cue and the onset of the dichotic trial (Stimulus Onset Asynchrony - SOA) was varied in order to control the time available to orient attention to the cued ear. Whereas performance for the right ear improved substantially with SOA, that for the left ear improved only marginally. In addition, because of this differential effect of the cue on right ear and left ear performance, the magnitude of the right ear advantage was inflated at 450 ms SOA from that apparent at 150 ms and 750 ms SOA. These findings are interpreted as evidence that, in contrast to right-handers, left-handers bias their attention toward the left ear. This relation between handedness and the direction of the attentional bias is shown to have important implications for the interpretation of perceptual asymmetries.     

Dichotic Ear Preference for C-V-C Words in Wernicke's and Broca's Aphasias

A dichotic listening task was administered to subjects with a relatively distinct Broca's aphasia, subjects with a relatively distinct Wernicke's aphasia, and normal subjects. The dichotic stimuli consisted of C-V-C words differing in initial consonant only. Subjects were instructed to respond only to the stimulus of which they were most sure by pointing to a picture representing the dichotic stimuli or foils. While normal subjects demonstrated the usual right ear effect, both the Broca's and Wernicke's aphasia groups demonstrated left ear effects. One salient explanation for these results was that any severe defect in the language systems of the left hemisphere affects the way that the left hemisphere processes linguistic information. It was postulated that left ear stimuli, which arrive at the left hemisphere later, disrupt the processing of right ear stimuli in subjects with aphasia. However, a more definitive explanation requires further research.     

Dichotic listening and focused attention in children with hemiplegic cerebral palsy

Abstract

Dichotic listening data are reported from children with left and right hemiplegia, compared with a normal, age-matched, control group. The dichotic listening test was performed under two different attentional instructions. The aim of the study was to investigate whether lateral injury to one hemisphere also affects the capacity to direct attention in a laterality task because of inattention. The dichotic task consisted of consonant-vowel syllables that were presented with two different instructions, to attend to the left- or right-ear stimulus. The results showed that the control children had a right-ear advantage during the forced-right attention instruction, and a small left-ear advantage during the forced-left instruction. The two hemiplegia groups, however, showed the same ear advantage irrespective of attentional instruction. The results are discussed in terms of hemi-inattention and hypoarousal of the lesioned hemisphere in children with hemiplegia.     

Lateral orientation, eye movements and dichotic listening.

Past studies have found that lateral orientation (eye or head turn) may influence hemispheric asymmetry on the dichotic listening task. The present work studied the effects of forced head and eye turn on a consonant-vowel dichotic test. Spontaneous conjugate lateral eye movements (CLEM) in response to questions were also measured. The subjects were 29 male and 25 female right-handed university students. The dichotic test was administered using a forced-attention method rather than free recall in order to control for attentional bias. As predicted, right lookers on the CLEM test, showed an enhanced right ear advantage while left lookers showed a diminished right ear advantage. This suggests that characteristic hemispheric arousal may enhance or inhibit asymmetry on perceptual laterality tests. No relationship was found between dichotic listening and forced head or eye turning. It was noted that past experiments may have failed to control for the attentional bias introduced by having the head or eyes turned to one direction.     

Lateral Orientation,Eye Movements and Dichotic Listening

Pas, studies have found that lateral orientation (eye or head turn) may influence hemispheric asymmetry on the dichotic listening task. The present work studied the effects of forced head and eye turn on a consonant-vowel dichotic test. Spontaneous conjugate lateral eye movements (CLEM) in response to questions were also measured. The subjects were 29 male and 25 female right-handed university students. The dichotic test was administered using a forced-attention method rather than free recall in order to control for attentional bias. As predicted, right lookers on the CLEM test, showed an enhanced right ear advantage while left lookers showed a diminished right ear advantage. This suggests that characteristic hemispheric arousal may enhance or inhibit asymmetry on perceptual laterality tests. No relationship was found between dichotic listening and forced head or eye turning. It was noted that past experiments may have failed to control for the attentional bias introduced by having the head or eyes turned to one direction.     

Left hemisphere dominance for rhythmic elements in dichotically-presented melodies

Right ear superiority was found for two groups of 24 subjects on a dichotic listening test of melodies each differing only in rhythm. In addition, no ear difference was found in the same two groups for a dichotic melodies test differing only in pitch or pitch pattern. Finally, the usual left ear superiority was seen for dichotic presentation of chords and the usual right ear superiority was seen for the dichotic presentation of digits. The results imply that in neither of the non-verbal (melodies) tests was the right hemisphere superior to the left. In fact for one test the reverse was true: the left hemisphere was superior to the right for melody recognition based on a rhythm cue. The apparent conflict between this and previous studies is explained by the notion that it is not the stimuli per se that govern hemispheric dominance, but rather the cognitive functioning required by the left and right hemispheres in order to process them.     

Hemispheric differentiation and category width

This study concerns the relationship between a cognitive style dimension, category width, and hemispheric differentiation. When lists of word pairs were presented simultaneously in a dichotic listening task to broad and narrow categorisers (all female, right-handed), both groups of subjects recalled more words presented to the right ear than those presented to the left ear; indicating left hemisphere's superiority in verbal processing. Both broad and narrow categorisers recalled a similar number of words in the right ear (left hemisphere), but the former recalled significantly more words in the left ear than did the latter. This finding is interpreted as meaning that narrow categorisers rely predominantly on the left hemisphere in verbal processing, and that in comparison with narrow categories, there is greater right hemispheric involvement in processing in the case of broad categorisers. The implication of this finding in terms of the differential processing strategies adopted by the two groups of individuals is discussed.     

Hemisphere specialisation and inter-hemispheric cooperation during a phonological task: Effect of lexicality as assessed by the divided visual field approach

In the presented experiment we explored the effect of lexicality on hemisphere specialisation and cooperation during a phonological task. The divided visual field (DVF) method with bilateral presentation (BVF) of redundant (identical) stimuli is considered an appropriate approach to assess inter-hemispheric cooperation (IHC). IHC is supposed to increase the efficiency of cognitive processes. Specifically, it has been shown that, compared to unilateral hemifield presentation, word processing is significantly more efficient if stimuli were presented under bilateral redundancy conditions. The performance enhancement during bilateral vs. unilateral presentation is called bilateral redundant gain (BRG). In the present experiment a DVF was used and participants were required to perform a rhyme detection task in two blocks, one in words and another one in pseudowords. Each item was presented in two different modes, one unilateral (right or left hemi-visual field) and another one bilateral (simultaneous redundant presentation). Unilateral trials allow one to study hemispheric specialisation, while bilateral redundant trials allow one to study inter-hemispheric cooperation. We obtained left hemisphere specialisation for both types of items (word, pseudoword). Moreover, words were more efficiently processed than pseudowords. Additionally, words were processed more efficiently in BVF than in unilateral presentation, inducing BRG. No similar effect was obtained for pseudowords. These results are discussed in respect to findings reported by other studies suggesting that hemispheric specialisation depends on lexicality. Moreover, compared to lexical decision tasks used in previous studies, the phonological task used in the present study seems to modulate the inter-hemispheric cooperation less.     

Functional brain asymmetry, attentional modulation, and interhemispheric transfer in boys with Tourette syndrome

We tested the hypothesis that children with Tourette syndrome (TS) would exhibit aberrant brain lateralization compared to a healthy control (HC) group in an attention-modulation version of a verbal dichotic listening task using consonant-vowel syllables. The modulation of attention to focus on the right ear stimulus in the dichotic listening situation is thought to involve the same prefrontal attentional and executive functions that are involved in the suppression of tics, whereas, performance when focusing attention on the left ear stimulus additionally involves a callosal transfer of information. In light of presumed disturbances in transfer of information across the corpus callosum, we hypothesized that children with TS would, however, have difficulty modulating the functional lateralization that ensues through a shift of attention to the left side. This hypothesis was tested by exploring the correlations between CC size and left ear score in the forced-left condition. Twenty boys with TS were compared with 20 age- and handedness-matched healthy boys. Results indicated similar performance in the TS and HC groups for lateralization of hemispheric function. TS subjects were also able to shift attention normally when instructed to focus on the right ear stimulus. When instructed to focus attention on the left ear stimulus, however, performance deteriorated in the TS group. Correlations with CC area further supported the hypothesized presence of deviant callosal functioning in the TS group.