The effects of head and eye turns on the right ear advantage in dichotic listening

The aim of the present experiment was to investigate the effects of head and eye turns on the ear advantage in dichotic listening (DL) to CV-syllables. Since head and eye turns also mean focusing attention to either the left or right side in space, a second aim was to evaluate recent arguments that ear advantages seen in DL are caused by the perceived position in space of the sound source. Forty right-handed females had 36 trials of CV-syllables under four different instructions. One group (n = 20) was instructed to turn their head (but not their eyes) to the right, the left, or straight ahead during stimulus presentations. The fourth condition was a standard (no instruction) condition. A second group (n = 20) had the same instructions but were told to turn their eyes instead of their heads. Conditions were pseudo-counterbalanced across subjects. Consistent with other studies, results showed a right ear advantage (REA) in both groups during all conditions. However, the REA was largest for the standard condition. Also, more subjects showed a REA during the standard condition, and especially compared to the turn-right condition. It is concluded that dichotic performance is not caused by selective attention to either side in space, and that lateral turns of the head and the eyes contralateral to the left hemisphere have an inhibitory (if anything) effect on the REA.     

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.     

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.     

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.     

The effects of background noise on dichotic listening to consonant-vowel syllables

Lateralization of verbal processing is frequently studied with the dichotic listening technique, yielding a so called right ear advantage (REA) to consonant-vowel (CV) syllables. However, little is known about how background noise affects the REA. To address this issue, we presented CV-syllables either in silence or with traffic background noise vs. 'babble'. Both 'babble' and traffic noise resulted in a smaller REA compared to the silent condition. The traffic noise, moreover, had a significantly greater negative effect on the REA than the 'babble', caused both by a decreased right ear response as well as an increased left ear response. The results are discussed in terms of alertness and attentional factors.     

Attentional Effects in Dichotic Listening

This study addresses attentional effects in dichotic listening (DL) to consonant-vowel syllables. Previous research has shown that ear advantages in DL are modulated by biased attention to either the left or the right ear. Attentional effects in DL can be the result of two processes: facilitation of reports from the attended ear, or suppression of intrusions from the nonattended ear. Sixty-two students were tested with DL under three different task instructions: nonforced (divided) attention, attention forced to the right ear, and attention forced to the left ear. The main finding was inhibition of intrusions from the nonattended ear, combined with the facilitation of the correct reports from the attended ear during the two forced-attention conditions, compared with the nonforced condition. The results are discussed in relation to right hemisphere processing of dichotic input, and that attention may activate subcortically biased asymmetries which suppress input from the nonattended channel.     

A dichotic listening study of attention control in older adults

The influence of age on attentional control of bottom-up processing was investigated with a dichotic-listening paradigm. The typical right-ear-advantage (REA) without specific attentional instructions was used as a measure of bottom-up processing (non-forced condition). Top-down attentional control was evaluated by instructing subjects to report only the right or left ear stimulus of the dichotic pair (forced-right, forced-left conditions). Both young and old participants showed a REA in the non-forced condition and an increased REA in the forced-right condition. The old group failed, however, to use attention to modulate the REA to the same degree as the younger participants in the forced-left condition. Only the young group showed a significant left ear advantage (LEA). The results are discussed in relation to cognitive decline in normal aging and in early stages of dementia.     

Dichotic listening performance and writing posture in right- and left-handers

Right-handers and left-handers with the inverted (IN) and noninverted (NI) writing posture were tested on a dichotic consonant-vowel listening task and on two motor tasks (hand strength and speed of tapping). The results failed to show the differences between IN and NI right-handers reported by S. M. Tapley and M. P. Bryden (1983, Neuropsychologia, 21, 129-138) and there were no significant handedness x writing posture x ear interactions. A significant interaction between dichotic listening performance and writing posture was found; NI right-handers and IN left-handers had more correct responses and fewer intrusions than IN right-handers and NI left-handers. Left-handers and right-handers were found to have a right ear advantage (REA) in the dichotic listening task but left-handers had relatively smaller left/right differences in all of the performance measures. Sample characteristics suggest that there are more IN male right-handers than IN female right-handers.     

Auditory neglect after right frontal lobe and right pulvinar thalamic lesions

Auditory unilateral neglect or extinction to simultaneous stimulation is reported in a right-handed male with a lesion in the right frontal lobe and in the right thalamic pulvinar area. The patient was submitted to stereotactic thalamotomy for a post-traumatic intentional ataxia in the left extremities. He was subjected to repeated tests with dichotic listening to consonant-vowel syllables under three different attentional instructions. He was also tested monaurally with the same stimulus materials as used in the dichotic test. The results showed almost complete extinction of the left ear input during dichotic presentations, despite normal hearing when tested with audiometer screening. The left ear extinction effect was independent of instructions to attend to the left or right ear input. However, during monaural presentation, correct left ear reports increased to about 85%. The results are interpreted as showing an auditory attentional neglect caused by the right frontal and pulvinar lesions.     

Information processing and speech lateralization in learning-disabled children

The relationship between information processing and speech lateralization was investigated in learning-disabled children. The Kaufman Assessment Battery for Children (K-ABC) assessed simultaneous and successive processing while a dichotic listening paradigm with free recall and directed attention conditions assessed speech lateralization. A three-factor ANOVA design conducted on the dichotic data revealed that normal children demonstrated stronger right ear advantage (REA); whereas learning-disabled showed weaker right ear advantage. Further, lambda analyses conducted on individual subjects revealed that the learning-disabled did not demonstrate the REA, were not biased attenders, and did not get more right ear than left ear items when attention was directed to one ear. Multiple-regression analysis was used to predict sequential processing from the dichotic data for both groups. Learning-disabled children demonstrated a substantial deficit in sequential processing as compared to normal children. These results indicate that learning-disabled children may not have adequate cerebral lateralization of receptive speech processes, shift their attention more readily, and are more inadequate in sequential processing that presumably subserves language functioning. Perhaps learning-disabled children have deficiencies of processor capacity of salient areas of the left (language) hemisphere.     

The effects of different intensity levels of background noise on dichotic listening to consonant-vowel syllables

It has previously been shown that the right ear advantage in dichotic listening to consonant-vowel syllables is affected if a background noise is presented at the same time as the dichotic stimuli. What is not known is, however, if there is also an effect of varying the intensity level of the background noise. We therefore presented conversation or traffic noise background noise simultaneously with the dichotic syllable stimuli to healthy adult subjects. The intensity of the background noises varied between 50-65 dB in steps of 5 dB. The results showed that the right ear correct reports decreased, while left ear correct reports increased as a consequence of increasing background noise intensity. The effects were also stronger for the right ear, and for the traffic background noise condition, particularly at the two highest intensity levels. The results are discussed in terms of alertness and attentional mechanisms.     

The fate of ear asymmetries in short-term memory

Recognition memory for word lists presented to left or right ears was tested after filled retention intervals of 0-to 60-sec duration. Experiment 1 showed that the right-ear advantage (REA) for immediate recognition in dichotic listening does not occur after 10 sec delay. In Experiment 2, monaural presentation produced a nonsignificant REA which did not appear to be affected by delay. These data suggest that the REA for immediate report usually observed in the dichotic listening situation is a transient phenomenon which is based on phonetic encoding. The left hemisphere seems to be specialized for the initial reception of verbal information, but not for the storage or retention of such information over time.     

Perceptual difficulty and the right ear advantage for vowels

The results of a series of four dichotic listening experiments confirm that under appropriate conditions vowels show a right ear advantage (REA) comparable to that of consonants. The conditions all cause perceptual difficulty, adversely affecting the accurate registration of both inputs in the auditory system. The addition of noise, shortening of the vowel stimuli, and the use of a more confusable set of vowels, each had the effect of increasing REA. Results are compatible with an explanation of ear advantage in terms of competition at the auditory rather than the phonetic level, in which short-term precategorical acoustic storage (PAS) may play a critical role.     

Dichotic listening with forced attention in patients with temporal lobe epilepsy: significance of left hemisphere cognitive dysfunction

Fifty right-handed patients with focal temporal lobe epilepsy were administered a dichotic listening test with consonant-vowel syllables under non-forced, forced right and forced left attention conditions, and a neuropsychological test battery. Dichotic listening performance was compared in subgroups with and without left hemisphere cognitive dysfunction, measured by the test battery, and in subgroups with left and right temporal epileptic focus. Left hemisphere cognitive dysfunction led to more correct responses to left ear stimuli in all three attention conditions, and fewer correct responses to right ear stimuli in the non-forced attention condition. This was probably caused by basic left hemisphere perceptual dysfunction. Dichotic listening was less affected by a left-sided epileptic focus than by left hemisphere cognitive dysfunction. General cognitive functioning influenced dichotic listening performance stronger in forced than in non-forced attention conditions. Larger cerebral networks were probably involved in the forced attention conditions due to the emphasis on conscious effort.     

Attentional set in pure- versus mixed-lists in a dichotic listening paradigm

An experiment was designed to assess the contribution of attentional set to performance on a forced choice recognition task in dichotic listening. Subjects were randomly assigned to one of three conditions: speech sounds composed of stop consonants, emotional nonspeech sounds, or a random combination of both. In the groups exposed to a single class of stimuli (pure-list), a REA (right ear advantage) emerged for the speech sounds, and a LE (left ear advantage) for the nonspeech sounds. Under mixed conditions using both classes of stimuli, no significant ear advantage was apparent, either globally or individually for the speech and nonspeech sounds. However, performance was more accurate for the left ear on nonspeech sounds and for the right ear for speech sounds, regardless of pure versus mixed placement. The results suggest that under divided attention conditions, attentional set influences the direction of the laterality effect.     

The effect of memory load on the right ear advantage in dichotic listening

The right ear advantage (REA) observed in dichotic tests was further investigated to examine the effects of memory load on the task. Memory load was operationally defined as the duration of time wherein subjects were asked to retain the stimuli, with no rehearsal, prior to recall. The delay periods interpolated between dichotic stimulation and recall were: no delay, 5, 10, and 15 sec delay. There was a significant REA in the no delay condition. The conditions with interpolated delay periods showed a substantial loss in overall accuracy, and at 15 sec delay showed a strong REA. The results offer suggestive evidence for a lateralized memory mechanism for storing speech sounds.     

Hormones and dichotic listening: evidence from the study of menstrual cycle effects

This report presents evidence for changes in dichotic listening asymmetries across the menstrual cycle, which replicate studies from our laboratory and others. Increases in the right ear advantage (REA) were present in women at phases of the menstrual cycle associated with higher levels of ovarian hormones. The data also revealed correlations between hormone levels and behavioural measures of asymmetry. For example, the pre-ovulatory surge in luteinising hormone (LH) was related to a decrease in left ear scores, which comprised a key part of the cycle related shift in asymmetry. Further analysis revealed a subgroup of women who had not reached postovulatory status by days 18-25 of the cycle, as verified by low progesterone levels. These women showed laterality profiles at days 18-25 that looked more like the other women when measured at the periovulatory phase (i.e., days 8-11). Data were combined with those from a previous study to highlight the stability of effects. Results showed a distinct menstrual cycle related increase in asymmetry in the combined sample. This final comparison confirmed the nature of sex differences in dichotic listening as being dependent on hormone status in women.     

The effect of stimulus type and directed attention on dichotic listening with children

This research investigated the effect of stimulus type and directed attention on dichotic listening performance with children. A sample of 12 (5 male, 7 female; mean age 10.5 years) high academically performing children were administered four types of dichotic stimuli (words, digits, CV syllables, and melodies) in three experimental conditions (free recall, directed left, and directed right) to examine perceptual asymmetry as reflected by the right-ear advantage (REA). While the expected REA for words and CV syllables and the expected LEA for melodies were found under free recall, the directed conditions produced varied results depending on the nature of the stimuli. Directed condition had no effect on recall of CV syllables but had a dramatic effect on recall of digits. Word stimuli and directed condition interacted to produce inconsistent perceptual asymmetry while directed condition reduced overall recall for melodies. The findings lend support to the hypothesis that perceptual asymmetries can be strongly influenced by the type of stimulus material used and the effect of attentional strategy employed.     

The role of the left and right thalamus in language asymmetry: dichotic listening in Parkinson patients undergoing stereotactic thalamotomy

Fourteen patients with Parkinson's disease (rigidity and unilateral tremor as main symptoms) were treated with stereotactic thalamotomy. The operation was performed in either the left or right ventrolateral thalamus, depending on which hand (or foot) was most affected with tremor. Nine patients were operated on the left side and four on the right side. All patients were tested for asymmetry of language functioning with dichotic presentations of consonant-vowel (CV) syllables. The patients had to indicate which of the two syllables he/she heard on each trial. Dichotic listening was performed before and after the operation, as well as during electrical stimulation of the VL nucleus just before the lesion was carried out. The results revealed essentially three things: an overall reduced right ear advantage (REA) in the patient group compared to what is known from studies of healthy individuals; an increase in REA during left-sided stimulations; and a marked reduction in REA after left-sided lesions. It is concluded that the present data support the notion put forward by Ojemann (e.g., 1975) of a lateralized activating gating mechanism in the left VL nucleus that gates access for language information to the appropriate cortical areas. The gating mechanism seems to be activated by stimulation, and deactivated after lesions. Dichotic listening may thus be a heuristic instrument in assessment of language functions in Parkinson patients.     

Dichotic listening performance to CVs between versus within groups

The present study is concerned with comparing group mean data between groups with individual performance within groups in dichotic listening (DL). It is argued that only comparing mean ear performance in dichotic listening between groups may obscure important individual differences within groups in DL performance. In the present study we compared between group vs. within group performance in four groups of subjects (male and female, right- and left-handers). The stimuli were 66 trials of consonant-vowel combinations with the six stop-consonants and the vowels a and u. The results showed a group mean right ear advantage for consonants in the two right-handed groups, and a left-ear advantage in the two let-handed groups. The analysis of the individual distributions within each group, however, showed clear differences between the male and female groups. Generally, though, only the male right-handed group revealed enough homogeneity within the group to warrant the conclusion that the group mean REA reflects a left hemisphere specialization for speech perception.