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.     

Attentional strategies in dichotic listening

A person can attend to a message in one ear while seemingly ignoring a simultaneously presented verbal message in the other ear. There is considerable controversy over the extent to which the unattended message is actually processed. This issue was investigated by presenting dichotic messages to which the listeners responded by buttonpressing (not shadowing) to color words occurring in the primary ear message while attempting to detect a target word in either the primary ear or secondary ear message. Less than 40% of the target words were detected in the secondary ear message, whereas for the primary ear message (and also for either ear in a control experiment), target detection was approximately 80%. Furthermore, there was a significant negative correlation between buttonpressing performance and secondary ear target-detection performance. The results were interpreted as being inconsistent with automatic processing theories of attention.     

Attention in dichotic listening: Affective cues and the influence of instructions

In shadowing one of two simultaneous messages presented dichotically, subjects are unable to report any of the content of the rejected message. Even if the rejected message consists of a short list of simple words repeated many times, a recognition test fails to reveal any trace of the list. If numbers are interpolated in prose passages presented for dichotic shadowing, no more are recalled from the rejected messages if the instructions are specifically to remember numbers than if the instructions are general: a specific set for numbers will not break through the attentional barrier set up in this task. The only stimulus so far found that will break through this barrier is the subject's own name. It is probably only material “important” to the subject that will break through the barrier.     

Children's recall strategies in dichotic listening

Normal adults spontaneously adopt different recall strategies in reporting dichotic material presented at different rates. A channel by channel or ear order is used with the faster rate of input and a pair by pair or temporal order is used with the slower rate of input. The purpose of the present report is to study the frequency of the different orders of report in children as a function of the rate of input of dichotic stimulation. Twenty-four normal children, 9–10 years of age, were given the dichotic listening task under three rate conditions. The children used different recall strategies as a function of rate of input in the same manner as that reported for adults. In addition, the order of presentation of the different rates of input was found to influence the relative frequency of the different recall strategies. A significant positive correlation was found between intelligence and the frequency of use of only the temporal recall strategy in its appropriate (slow) rate condition.     

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.     

Hemispheric asymmetry effects in children studied by dichotic listening and visual half-field testing

Dichotic listening (DL) and visual half-field (VHF) testing were used to study hemisphere asymmetry in a developmental perspective. Five-, 8-, and 11-year-old children were presented lists of fused words using a DL technique in Experiment 1, and 8- and 11-year-old children were presented pictures of common objects using a VHF technique in Experiment 2. In both experiments, measures of identification, free recall, and recognition of the words/pictures were employed. The results revealed effects of ear input (right-ear advantage) and half-field presentation (right visual half-field advantage) for all age groups, although the magnitude of this lateralization effect differed between the three memory measures. The results are discussed in relation to developmental aspects of language laterality, and in relation to the clinical utility of non-invasive lateralization techniques.     

Hemispheric emotional asymmetry in a dichotic listening task.

In a dichotic listening experiment white noise was played to one ear and either music or poetry to the other ear. Subjects rated the stimuli on each of three dimensions. The results showed that both music poetry were judged as more pleasant when heard at the left than the right ear. In addition the music, but not the poetry, was perceived as more soothing at the left ear. The findings are discussed in relation to other indications in the literature that left and right cerebral hemispheres differ in their emotional make-up.     

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.     

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.     

Time sharing and dichotic listening asymmetry in normal and learning-disabled children

Time-sharing and dichotic listening techniques were used to examine cerebral lateralization for language function in 48 normal and 48 learning-disabled children. All subjects were matched according to age, sex, and handedness. An analysis of results indicated that both nornal and learning-disabled children demonstrated left hemisphere lateralization of language function on the time-sharing and dichotic listening tasks. However, no developmental trends were evident for either group. Differences observed in the performance of the normal and learning-disabled children may relate to how each group utilizes “verbal strategies” and processes simultaneous information in the left hemisphere. The results strongly question the notion that attributes learning disabilities to incomplete or delayed language lateralization and lend support to the notion that cerebral lateralization is not a developmental phenomena.     

Development of cerebral dominance: dichotic listening asymmetry in normal and learning-disabled children

The magnitude of the dichotic right-ear advantage was assessed in 48 normal and 48 learning-disabled children representing an age range of approximately 5 years. All subjects were matched according to age, sex, and handedness. An analysis of results indicated a significant right-ear advantage in both the normal and learning-disabled children, but revealed no developmental trends for either group. Differences observed in the performance of the learning-disabled and normal children may reflect variability in selective attention rather than differences in the degree of cerebral lateralization. These results suggest a need for a reconceptualization of the causative factors affecting children with learning disorders and lend support to the notion that cerebral lateralization is not a developmental phenomenon.     

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.     

Dichotic listening ear asymmetry: Patterns of longitudinal development

Dichotic listening research with children has continued to be prevalent although numerous authors have described both theoretical and methodological limitations with traditional dichotic listening free-recall paradigms. The present research adds to this growing skepticism by reanalyzing two major longitudinal studies of children's ear asymmetries. These two studies, based in different countries (United States, Holland), utilized highly similar paradigms (free-recall digits), subjects (males), and age levels (kindergarten and second and fifth grade). The questions of ear advantage development, patterns of ear advantages, and the relationship between dichotic listening performance and reading skills are addressed from the multiple statistical methodologies represented in the literature. From these analyses, support for all of the major hypotheses regarding the developmental patterns of dichotic listening performances could be obtained from the same data samples. The use of traditional free-recall dichotic listening paradigms are not recommended for use with children. The implications for future research are discussed.     

Effects of hemispheric asymmetry on electrodermal conditioning in a dichotic listening paradigm

It was predicted that when an auditive verbal conditional stimulus (CS+), previously associated with an aversive unconditional stimulus (UCS), is presented to theright ear (initial left hemisphere input), in a dichotic listening task, with the CS-simultaneously presented in the left ear, the result would be greater resistance to extinction than when the same CS+ is presented to the left ear (initial right hemisphere input). In the same vein, it was predicted that, when a tonal CS+ is presented to theleft ear, greater resistance to extinction would occur as compared with when it is presented to the right ear. During a dichotic test phase, each group was split into two subgroups, and the CS+ and CS—repeatedly were presented simultaneously to each ear. Half of the subjects in each subgroup had the CS+ presented to the left ear. The other half had the CS+ presented to the right ear. Skin conductance responses were recorded from both hands. Results showed significantly larger responding in all groups to the CS+/UCS compound during the acquisition phase. However, during the dichotic extinction phase, the verbal CS+ right-ear subgroup showed significantly larger resistance to extinction as compared with the verbal CS+ left-ear subgroup. No differences were found between the two tonal subgroups.     

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.