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.     

Stimulus intensity, attentional instructions, and the ear advantage during dichotic listening

The present experiment was designed to investigate the effects of the following two variables on the identification of dichotically presented CV syllables: (1) the relative difference in intensity levels of the stimuli presented to the two ears and (2) the instructions to attend to both ears or to focus attention on one ear. As expected for a verbal task, more CV's were identified from the right ear than from the left ear. Furthermore, identification of stimuli presented to one ear improved when (1) those stimuli were relatively higher in volume than the stimuli presented to the other ear and (2) when subjects were instructed to focus attention on only that ear rather than distribute attention across both ears. Of particular importance is the finding that the effects of relative stimulus intensity are the same under conditions of focused attention as under conditions of divided attention. This finding is inconsistent with an attention explantation of the relative intensity effects. Instead, the results are consistent with a model of dichotic listening in which ear of stimulus presentation and relative stimulus intensity influence a perceptual stage of information processing and attentional instructions influence a subsequent response selection stage.     

The effects of attention on ear advantages in dichotic listening to words and affects

This study examined the effects of attention on ear advantages using dichotic listening to words and affects, a focused-attention paradigm. We compared the mixed condition, in which attention is switched between the ears in each trial, to the blocked condition, in which attention is directed to one ear for an entire block of trials. Results showed a decreased right ear advantage for word processing only in the mixed condition and an increased left ear advantage for emotion processing in both attention conditions for hits index. The mixed condition showed smaller laterality effects than the blocked condition for words with respect to hits index, while increasing right ear predominance for intrusions. The greater percentage of intrusions in the right ear for the word task and in the mixed condition suggests that the right ear (left hemisphere) is most vulnerable to attention switching. We posit that the attention manipulation has a greater effect on word processing than on emotion processing and propose that ear advantages reflect a combination of the effects of attentional and structural constraints on lateralisation.     

Pure-tone perception and ear advantages in dichotic listening

A same-different matching task was used to investigate how subjects perceived a dichotic pair of pure tones. Pairs of stimulus tones in four frequency ranges (center frequencies of 400–1,700 Hz), with separations between 40 and 400 Hzt were tested. Five types of test tones were matched to the stimulus pair: the stimulus pair presented again (control) or crossed over (same tones, different ears), the geometric mean of the two tones, or a binaural tone of the low or high tone of the pair. In the lowest frequency range and the highest with maximum separation, the crossed-over test tones were perceived as different from the same stimulus tones. A bias for perceiving the higher tone of a pair was evident in the frequency ranges with separations of 40-200 Hz. In the lowest frequency range, the bias was for perceiving the higher tone in the right ear. This restricted ear advantage in the perception of pure tones was not significantly related to the right-ear advantage in dichotic word monitoring.     

A right-ear advantage for dichotic listening in bilingual children

A dichotic listening task was administered to two groups of right-handed Hispanic children enrolled in bilingual education classes. The younger group's mean age was 9:6, the older group's was 13:6. Two dichotic tapes were used, one in English, one in Spanish, consisting of 60 pairs of words per tape. The words were comparable across languages in terms of frequency, grammatical function, and phonetic composition. The results showed clear and equal right-ear advantages for both groups of subjects and for both languages. As expected, older children scored higher than younger ones, and performance on Spanish was better than on English. Neither of these effects interacted with the ear advantage, however. Ear difference scores did not correlate with proficiency in the second language (as measured by performance on the English tape), but there was a significant correlation (r = .58) between the degree of asymmetry in the two languages. These findings indicate that the left hemisphere is primarily (and equally) involved in processing both languages of bilinguals, and that this pattern appears to remain stable in development.     

Large individual differences in minor ear output during dichotic listening

Using dichotic consonant-vowel (CV) stimuli, 150 highly educated adults were segregated into two groups. In the high-output group (n = 63), the mean number of CV syllables reported by the minor ear was more than half that of the major ear, while for the low-output group (n = 87), it was less than one-fourth. The low minor ear performance of the latter group immediately disappeared when CV syllables were separated by 90 ms. These subjects (44 male, 43 females) were unaware of their temporary minor ear incapacities. Although the mechanism and brain laterality significance of this phenomenon remain to be clarified, preliminary research indicates that members of each of these two groups have other differences in common.     

Hemispheric dominance, dichotic listening and lateral eye movement behaviour

Abstract.— Because lateral corrective eye movements have been shown to influence the results of the dichotic listening test, it was supposed that differences in the scoring on this test by right and left eye movers could be found. Only in the entire group of 22 right handed subjects and in the subgroup of 8 right eye movers a significant right ear superiority was found. In the left mover group (14 subjects) right ear superiority in dichotic listening was not significant. These results are interpreted in terms of possible interhemispheric differences in the level of "activity", facilitating or hampering perception of verbal material in the contralateral ear.     

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.     

The syntagmatic-paradigmatic shift in dichotic listening

Children at two age levels, 6 to 7 years and 9 to 10 years, listened to pairs of words presented dichotically to the left and right ear either simultaneously or in immediate succession. Their task was to report what they heard after each pair. The experimental pairs involved either syntagmatic relations (e.g., bird-fly) or paradigmatic relations (table-chair). The younger children correctly identified more syntagmatic than paradigmatic pairs (using control pairs as a base) while the older children correctly identified more paradigmatic pairs. There was no difference between associated and nonassociated pairs. The results are taken to mean that pragmatic, serial relations dominate the semantic organization of younger children and that logical, hierarchical relations make their impact later in the course of development.     

Left ear dichotic listening performance on consonant-vowel combinations and digits in subtypes of reading-disabled children

Twenty reading comprehension-disabled (CD) and 20 reading comprehension and word recognition-disabled (CWRD), right-handed male children were matched with 20 normal-achieving age-matched controls and 20 normal-achieving reading level-matched controls and tested for left ear report on dichotic listening tasks using digits and consonant-vowel combinations (CVs). Left ear report for CVs and digits did not correlate for any of the groups. Both reading-disabled groups showed lower left ear report on digits. On CVs the CD group showed a high left ear report but only when there were no priming precursors, such as directions to attend right first and to process digits first. Priming effects interfered with the processing of both digits and CVs. Theoretically, the CWRD group seems to be characterized by a depressed right hemisphere, whereas the CD group may have a more labile right hemisphere, perhaps tending to overengagement for CV tasks but vulnerable to situational precursors in the form of priming effects. Implications extend to (1) subtyping practices in research with the learning-disabled, (2) inferences drawn from studies using different dichotic stimuli, and (3) the neuropsychology of reading disorders.     

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.     

Perspectives on dichotic listening and the corpus callosum

The present review summarizes historic and recent research which has investigated the role of the corpus callosum in dichotic processing within the context of audiology. Examination of performance by certain clinical groups, including split brain patients, multiple sclerosis cases, and other types of neurological lesions is included. Maturational, age related, and genetic factors are also discussed. Finally, some attention is given to recent trends in audiology research to develop improved diagnostic and rehabilitation tools for individuals with dichotic deficits potentially related to callosal dysfunction.     

Left ear (right temporal lobe) suppressions during dichotic listening, ego-alien intrusion experiences and spiritualistic beliefs in normal women.

Beliefs in spiritualism, a history of a sensed presence, and mental diplopia may share a common source of psychometric variance. We hypothesized that this variance should be specifically associated with right temporal-lobe function. Inferences of temporal lobe signs, hemisphericity (Vingiano's quotient) and self-esteem as well as dichotic listening measures were obtained for 26 university women. As predicted, the numbers of left-ear suppressions (right temporal-lobe function) but not of right-ear suppressions were specifically and moderately (rho = 0.64) correlated with the intensity of Tobacyk's spiritualistic beliefs and a history of sensed presences and ego-alien intrusions. However, the negative association (rhos about -0.45) between indices of left-right hemisphericity and self-esteem was related to a separate factor.     

The development of handedness and dichotic ear listening asymmetries in relation to school achievement: A longitudinal study

To assess the development of dichotic ear asymmetries and handedness, 208 male school children were evaluated in kindergarten and at Grades 2 and 5 (ages 66, 92, and 130 months of age, respectively) with a dichotic listening task and a hand preference test. The Wide Range Achievement Test (WRAT) also was administered at each of the three grade levels. There was significant variability in handedness scores over time only for those subjects whose scores at initial testing, that is, in kindergarten, identified them as non-right-handers. Both right and left handers had a significant increase in dichotic listening scores over time; however, only right handers had a significant right ear advantage at each evaluation. Regression analyses showed that combined hand preference scores and ear recall scores at each probe when combined accounted for almost 44% of the variance in WRAT achievement scores at Grade 5. Ear asymmetry scores, however, were not predictive of school achievement.