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.     

Simultaneous masking in a dichotic emotion detection task

The present study investigated the possible role of ceiling effects in producing laterality effects of small magnitude in dichotic emotion detection. Twenty two right-handed undergraduate students participated in the present experiment. They were required to detect the presence of a target emotion in the expressions tones of happiness, sadness, anger, and neutrality presented dichotically. Stimuli were adjusted to 70 dB and occurred simultaneously with a white noise mask that had an intensity of 65, 70, 80, or 85 dB. Results showed a left ear advantage (LEA) for the 65 dB mask and a right ear advantage for the 85 dB mask, but only after two testing sessions. The possible existence of a generalized right ear bias that might affect the observed LEA for non-verbal tasks is discussed. Alternative explanations and limitations of the present experiment are also presented.     

Response competition and target word detection during shadowing in a dichotic listening task

College students (N = 24) served as subjects in a within-subjects study of auditory attention in which four tasks were performed. In the easiest task, a single passage was presented and shadowed while target word detections were indicated by pressing a key. The other three tasks also required target word detection, but a second passage was presented simultaneously. One task had no target words in the unshadowed passage; the other two tasks required a key-pressing response to the target words in both passages, either with one hand or with each hand. We expected performance to decrease as task complexity increased; this was partially confirmed. The task of shadowing and detecting target words is too difficult to be used to test perception or response limitations of attention.     

The processing of fundamental frequency in a dichotic matching task

The temporal characteristics of auditory memory were investigated using a reaction time paradigm. The study attempted to determine whether or not there are functionally distinct left and right hemisphere components of auditory memory with different capacities for the retention of nonlinguistic information, such as fundamental frequency, over the course of several seconds. The results indicated that fundamental frequency information in auditory memory remains substantially unchanged over the course of 2 sec. No evidence was found for the existence of separate left and right hemisphere components of auditory memory with different temporal characteristics. The implications of this finding for the organization of auditory memory in the brain 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.     

Hemispheric performance in detecting prosody: a competitive dichotic listening task

Ross's 1981 model of right-hemisphere processing of affective speech components was investigated within the dichotic paradigm. A spoken sentence constant in semantic content but varying among mad, sad, and glad emotional tones was presented to 45 male and 45 female college students. Duration of stimuli was controlled by adjusting digital sound samples to a uniform length. No effect of sex emerged, but the hypothesized ear advantage was found: more correct identifications were made with the left ear than with the right. A main effect of prosody was also observed, with significantly poorer performance in identifying the sad tone; in addition, sad condition scores for the right ear were more greatly depressed than those for the left ear, resulting in a significant interaction of ear and prosody.     

Ear asymmetries in dichotic listening tasks which increase in difficulty

Accuracy and laterality of ear preference in repeating 2, 3 and 4 word pairs (WP) of dichotic stimuli in English and French were determined in 80 right-handed subjects (anglophone/francophone, male/female), who were tested in both their native language (L1) and nonnative language (L2). Relative performance accuracy decreased as a function of word pairs per trial (from 2 to 4) as well as language (from L1 to L2). Right-lateral preference in turn increased as a function of WP (from 2 to 4) as well as language (L1 to L2). Right-ear advantage (REA) in L2 decreased as a function of language proficiency (low to high). REA was observed in over 90% of subjects. A rationale for greater lateralization of L2 performance is offered.     

Temporal characteristics of primary-secondary message interference in a dichotic listening task

Previous experiments have shown that during performance of a shadowing task the unattended message is processed at a semantic level. Four experiments are reported that deal with the question of how processing of the unattended message influences the difficulty of shadowing the attended message. Experiment I demonstrated that pupil dilation measures the difficulty associated with a shadowing task. In Experiment II it was shown that during shadowing of 20-item lists pupil dilation decreases as shadowing continues when either words or white noise are in the unattended channel. These results support the idea that it takes time for the attentional mechanism to focus on the attended message. In Experiments III and IV it was found that this decrease in difficulty of shadowing is much less when the attended and unattended messages come from the same stimulus category (letter-letter, digit-digit). The results indicate that, when the unattended message is from the same stimulus category as the attended message, it can interfere with the ability of the attentional system to focus on the attended message.     

Ear asymmetries on a selective attentional task

To ascertain whether there are ear-hemisphere asymmetries of selective attention, signal stimuli (tonal sequences) were presented monaurally with and without complex maskers (music and speech). The right ear-left hemisphere was more disrupted by language maskers; the left ear-right hemisphere was more disrupted by music maskers. These results suggest that there are hemispheric asymmetries of selective attention and that the ear hemisphere that usually processes a class of stimuli has greater difficulty filtering out those stimuli than does the nonspecialized hemisphere.     

Ear asymmetry in recognition of unfamiliar voices

Female right-handed subjects were presented with a memory set consisting of five unfamiliar female voices. They were then tested with a recognition procedure in which samples of voice, memory set or novel, 2 or 4 sec in duration, were heard in one ear and a competing noise stimulus was heard in the other ear. There was an overall left-ear advantage in accuracy of recognition. This advantage held particularly for identifications of memory-set voices in the second half of trials. Internal analyses indicated that the left-ear advantage could not be attributed to greater retroactive interference during right-ear presentation. Congruent with studies of recognition of unfamiliar faces, the findings suggested right-hemisphere superiority in the recognition of unfamiliar voices.     

Reliability of laterality effects in a dichotic listening task with nonverbal material

The present study examined the reliability of a dichotic listening task using nonverbal stimuli. Twenty undergraduate students (all right-handed native English speakers) had to report whether they had heard a target emotion. The task used English words (bower, dower, power, tower) pronounced with an angry, happy, neutral, or sad emotional tone. Results showed a relatively high level of test-retest reliability for the laterality effect. In addition, a significant gender by ear of presentation interaction was obtained. The interaction reflected the fact that a strong left ear advantage was found in females but not in males. The findings indicate that the task used here should be considered a reliable means to assess the lateralization of emotions. Issues concerning the relation between gender and laterality are addressed in the discussion.     

Reliability of a dichotic consonant-vowel pairs task using an ABX procedure

The present study examined the reliability of a dichotic consonant-vowels (CV) pairs task using an ABX procedure. Twenty-four right-handed subjects (12 females, 12 males) completed a dichotic CV pairs task twice in a test-retest approach. The conventional free-recall or directed-attention procedure was replaced by an ABX procedure, in which participants were required to determine whether a CV heard binaurally was present in a dichotic pair presented on the same trial. Results showed the expected right-ear advantage in dichotic listening for verbal material. However, reliability was not as high as has been reported with a directed-attention procedure. Methods for improving the reliability of the ABX discrimination task are discussed. In addition, the discussion emphasizes the usefulness of the ABX approach for testing clinical populations.     

Ear advantage and consonance of dichotic pitch intervals in absolute-pitch possessors

Left-right asymmetry in the central processing of musical consonance was investigated by dichotic listening tasks. Two piano tones paired at various pitch intervals (1-11 semitones) were presented one note in each ear to twenty absolute-pitch possessors. As a result, a weak overall trend for left ear advantage (LEA) was found, as is characteristic of trained musicians. Second, pitches of dissonant intervals were more difficult to identify than those of consonant intervals. Finally, the LEA was greater with dissonant intervals than with consonant intervals. As the tones were dichotically presented, the results indicated that the central auditory system could distinguish between consonant and dissonant intervals without initial processing of pitch-pitch relations in the cochlea.     

Reliability of laterality effects in a dichotic listening task with words and syllables

Large and reliable laterality effects have been found using a dichotic target detection task in a recent experiment using word stimuli pronounced with an emotional component. The present study tested the hypothesis that the magnitude and reliability of the laterality effects would increase with the removal of the emotional component and variations in word frequency. Thirty-two participants completed both a dichotic syllable detection task and a dichotic word detection task. In both tasks, stimuli were pronounced in a neutral tone of voice. Each task was completed twice to allow the estimation of test-retest reliability. Results failed to confirm the hypothesis since they were generally similar to those obtained in the previous study. A significant right ear advantage (REA) was found only with the word task. Although no ear advantage was found for the syllable task, somewhat better reliability was demonstrated compared to that obtained with words. The present findings suggest that including an emotional component does not reduce the reliability or magnitude of auditory laterality effects. In fact, the emotional component may have forced participants to focus on the language aspects of the stimuli. This might partly account for the reduced reliability in words and the absence of REA in syllables. Motivational factors inherent to the within-subject design used here are also discussed.     

Orientation asymmetry in the flanker task

Experiments 1 and 2 of this study show that when the target is either a vertical or a horizontal line, diagonal-line flankers tilted 45° either to the right or to the left have the same effect as do incongruent flankers. When the target is a diagonal line tilted either to the right or to the left, vertical- or horizontal-line flankers do not have the same effect as do incongruent flankers. Experiment 3 demonstrates that this asymmetry is not caused by the temporal-dynamic aspects of the processing. Together, these experiments suggest that there is an asymmetrical relation between diagonal lines and either vertical or horizontal lines otttside of the central focus of attention. Experiment 4 shows that despite this asymmetry in the flanker task, visual search for a vertical- or a horizontal-line target among diagonal-line distractors is not affected by the number of distractors. Possible explanations of this phenomenon are discussed.