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.     

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 in children: age-related changes in direction and magnitude of ear advantage

Children between the ages of 5 and 12 years were tested with dichotic listening tests utilizing single syllable words and random presentations of digits. They produced a higher prevalence of left ear dominance than expected, especially among right-handed children when tested with words. Whether more children demonstrate the LEA because of right hemisphere dominance for language or because there is less stability in ear advantage direction at younger ages cannot be fully resolved by this study. When ear advantages were measured by subtracting each child's lower score from the higher score without regard to right or left direction, an age-related trend toward lower measures of ear advantage was evident. This trend was greater for dichotic words than for dichotic digits. Structural factors that may be related to these results and possible influences of attention and verbal workload on the two kinds of dichotic stimuli are discussed.     

Valence specific laterality effects in prosody: expectancy account and the effects of morphed prosody and stimulus lead

The majority of studies have demonstrated a right hemisphere (RH) advantage for the perception of emotions. Other studies have found that the involvement of each hemisphere is valence specific, with the RH better at perceiving negative emotions and the LH better at perceiving positive emotions [Reuter-Lorenz, P., & Davidson, R.J. (1981) Differential contributions of the 2 cerebral hemispheres to the perception of happy and sad faces. Neuropsychologia, 19, 609-613]. To account for valence laterality effects in emotion perception we propose an 'expectancy' hypothesis which suggests that valence effects are obtained when the top-down expectancy to perceive an emotion outweighs the strength of bottom-up perceptual information enabling the discrimination of an emotion. A dichotic listening task was used to examine alternative explanations of valence effects in emotion perception. Emotional sentences (spoken in a happy or sad tone of voice), and morphed-happy and morphed-sad sentences (which blended a neutral version of the sentence with the pitch of the emotion sentence) were paired with neutral versions of each sentence and presented dichotically. A control condition was also used, consisting of two identical neutral sentences presented dichotically, with one channel arriving before the other by 7 ms. In support of the RH hypothesis there was a left ear advantage for the perception of sad and happy emotional sentences. However, morphed sentences showed no ear advantage, suggesting that the RH is specialised for the perception of genuine emotions and that a laterality effect may be a useful tool for the detection of fake emotion. Finally, for the control condition we obtained an interaction between the expected emotion and the effect of ear lead. Participants tended to select the ear that received the sentence first, when they expected a 'sad' sentence, but not when they expected a 'happy' sentence. The results are discussed in relation to the different theoretical explanations of valence laterality effects in emotion perception.     

The sad, the angry, and the asymmetrical brain: dichotic listening studies of negative affect and depression

Dichotic Listening (DL) is a valuable tool to study emotional brain lateralization. Regarding the perception of sadness and anger through affective prosody, the main finding has been a left ear advantage (LEA) for the sad but contradictory data for the anger prosody. Regarding an induced mood in the laboratory, its consequences upon DL were a diminished right ear advantage (REA) for the induction of sadness and an increased REA for the induction of anger. The global results fit with the approach-withdrawal motivational model of emotional processing, pointing to sadness as a right hemisphere emotion but anger processed bilaterally or even in the left hemisphere, depending on the subject's preferred mode of expression. On the other hand, the study of DL in clinically depressed patients found an abnormally larger REA in verbal DL tasks which was predictive of therapeutic pharmacological response. However, the mobilization of the available left hemisphere resources in these responders (reflected in a higher REA) would indicate a remission of the episode but would not assure the absence of new relapses.     

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.     

Hemispheric asymmetry in the perception of emotional sounds

Three experiments were conducted to investigate hemispheric asymmetry for the perception of emotional sounds. Pairs of human nonspeech sounds were presented dichotically in a forced choice recognition task. Under divided attention conditions (Experiments 1 and 2) an left ear advantage (LEA) emerged during the second block of trials. Performance accuracy for the left and right ears was equal during the first block of trials. Under selective attention conditions (Experiment 3) an LEA emerged during the first block of trials. The results suggest that attention influences the rate of development of the laterality effect but not the direction of the effect.     

Binaural loudness gain measured by simple reaction time

In order to yield equal loudness, different studies using scaling or matching methods have found binaural level differences between monaural and diotic presentations ranging from less than 2 dB to as much as 10 dB. In the present study, a reaction time methodology was employed to measure the binaural level difference producing equal reaction time (BLDERT). Participants had to respond to the onset of 1-kHz pure tones with sound pressure levels ranging from 45 to 85 dB, and being presented to the right, the left, or both ears. Equal RTs for monaural and diotic presentation (BLDERTs) were obtained with a level difference of approximately 5 dB. A second experiment showed that different results obtained for the left and right ear are largely due to the responding hand, with ipsilateral responses being faster than contralateral ones. A third experiment investigated the BLDERT for dichotic stimuli, tracing the transition between binaural and monaural stimulation. The results of all three RT experiments are consistent with current models of binaural loudness and contradict earlier claims of perfect binaural summation.     

Ear differences in the recall of fricatives and vowels

Two experiments on the free recall of dichotically presented synthetic speech sounds are reported. The first shows that the right ear advantage for initial fricative consonants is not simply a function of the recognition response class, but that it is also a function of the particular acoustic cues used to achieve that response. This is true both for the whole response, and for the constituent phonetic features. The second experiment shows that when both the response class and the particular stimuli presented on certain trials are held constant, the right ear advantage for the constant stimuli can be influenced by the range of other stimuli occurring in the experiment. Vowels show a right ear advantage when, within the experiment, there is uncertainty as to vocal tract size, but they show no ear advantage when all the vowels in the experiment are from the same vocal tract. These results are interpreted as demonstrating that there are differences between the ears, and probably between the hemispheres, at some stage between the acoustic analysis of the signal and its identification as a phonetic category.     

Cerebral specialization and verbal-motor integration in adults with and without Down syndrome

Persons with Down syndrome (DS) tend to exhibit an atypical left ear-right hemisphere advantage (LEA) for the perception of speech sounds. In the present study, a recent adaptation of the dichotic listening procedure was employed to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Although adults with DS (n = 13) demonstrated a right ear-left hemisphere advantage in the dichotic-motor task similar to their peers with (n = 14) and without undifferentiated developmental disabilities (n = 14), they showed an LEA in a free recall dichotic listening task. Based on a comparison of the laterality indices obtained from both dichotic listening procedures, it appears that the manifestation of lateral ear advantages in persons DS may dependent on the response requirements of the task.     

A dissociation of right and left hemispheric effects for recognizing emotional tone and verbal content

Emotionally intoned sentences (happy, sad, angry, and neutral voices) were dichotically paired with monotone sentences. A left ear advantage was found for recognizing emotional intonation, while a simultaneous right ear advantage was found for recognizing the verbal content of the sentences. The results indicate a right hemispheric superiority in recognizing emotional stimuli. These findings are most reasonably attributed to differential lateralization of emotional functions, rather than to subject strategy effects. No evidence was found to support a hypothesis that each hemisphere is involved in processing different types of emotion.     

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.     

Role of motion signals in recognizing subtle facial expressions of emotion

Three studies investigated the importance of movement for the recognition of subtle and intense expressions of emotion. In the first experiment, 36 facial emotion displays were duplicated in three conditions either upright or inverted in orientation. A dynamic condition addressed the perception of motion by using four still frames run together to encapsulate a moving sequence to show the expression emerging from neutral to the subtle emotion. The multi‐static condition contained the same four stills presented in succession, but with a visual noise mask (200 ms) between each frame to disrupt the apparent motion, whilst in the single‐static condition, only the last still image (subtle expression) was presented. Results showed a significant advantage for the dynamic condition, over the single‐ and multi‐static conditions, suggesting that motion signals provide a more accurate and robust mental representation of the expression. A second experiment demonstrated that the advantage of movement was reduced with expressions of a higher intensity, and the results of the third experiment showed that the advantage for the dynamic condition for recognizing subtle emotions was due to the motion signal rather than additional static information contained in the sequence. It is concluded that motion signals associated with the emergence of facial expressions can be a useful cue in the recognition process, especially when the expressions are subtle.     

Dichotic listening and sleep deprivation: vigilance effects

Twelve sleep-deprived and 13 non-deprived Navy cadets were tested with the dichotic listening procedure for effects of sleep deprivation on hemispheric asymmetry and sustained attention. Consonant-vowel syllables were presented to the subjects in three different conditions, a divided (non-forced) attention condition, a forced right ear and a forced left ear attention condition. In the two forced attention conditions the subjects were instructed to focus attention only on the right or left ear stimulus. The results showed an expected right ear advantage for both groups during the non-forced and forced right attention conditions, indicating superior left hemisphere processing. During the forced left attention condition, the sleep-deprived subjects showed no ear advantage at all, while the non-deprived subjects showed an expected left ear advantage. The results are discussed within a theoretical framework of a dual process model, where sleep deprivation disrupts the ability to sustain attention, caused by a temporary failure of the right hemisphere's top-down (instruction-driven) processing to override the left hemisphere's bottom-up (stimulus-driven) processing.     

Hemispheric laterality and dissociative tendencies: differences in emotional processing in a dichotic listening task

The present work investigates whether the hemispheric processing of both verbal and emotional stimuli, studied by means of a dichotic listening task, differs between normal high and low dissociators as assessed by the Dissociative Experiences Scale (DES; Bernstein & Putnam (1986). Development, reliability and validity of a dissociation scale. Journal of Nervous and Mental Disease, 174(2), 727-735). Two groups of subjects (50 high and 50 low dissociators), participated in the experiment. The task consisted in identifying both verbal and emotional stimulus-targets, respectively, on successive sessions. Reaction time and response accuracy were registered and analysed using ANOVA (Analysis of Variance). The interaction between stimuli (verbal, emotional), channel (right ear, left ear), and dissociation level (high, low) reached statistical significance in terms of accuracy measures (d': F(1,98)=4.75; p<.05). Both high and low dissociators exhibited the expected right ear advantage (REA effect) on verbal targets. On the other hand, whereas low dissociators exhibited the expected left ear advantage (LEA effect) on emotional targets, high dissociators failed to follow this typical pattern of hemispheric asymmetry: both hemispheres exhibited similar performances. These results confirm the hypothesis that dissociation is related to changes in hemispheric processing, specifically of emotional information.     

Modulation of motor area activity during observation of unnatural body movements

We investigated the processes underlying stimulus-response compatibility by using a lateralized auditory stimulus in a simple and choice reaction time (RT) paradigm. Participants were asked to make either a left or right key lift in response to either a control (80 dB) or startling (124 dB) stimulus presented to either the left ear, right ear, or both ears. In the simple RT paradigm, we did not find a compatibility effect for either control or startle trials but did find a right-ear advantage which we attribute to anatomical asymmetry of auditory pathways. In the choice RT paradigm, we found compatibility effects for both startle and control trials as well a high incidence of error for contralateral stimulus-response mapping. We attribute these results to automatic activation of the ipsilateral response, which must then be inhibited prior to initiation of the correct response. The presence of compatibility effects for startle trials also suggest that similar pathways are being used to initiate movements in a choice RT situation, as opposed to involuntary triggering that is thought to occur in a simple RT situation.     

Auditory lateralization: An effect of rhythm

Recall of monaurally presented semantically anomalous sentences, which had either neutral or rhythmic timing, was tested at the right ear, at the left ear, and on transfer from one ear to the other. The component words, being computer stored digitized waveforms, had identical acoustic structure in the two conditions. In the rhythmic condition there was not only an overall advantage in the second half of the experiment but also an asymmetric transfer effect such that this advantage did not appear when the left ear was tested after the right. It is proposed that functional lateralization be viewed as an adaptive, dynamic, organizational factor.     

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.     

Effects of chlorpromazine on lateralization,cued reaction time,and dichotic listening

In a double-blind cross-over design sixteen subjects took 50 mg of chlorpromazine or placebo in tablet form 2 hours prior to completing a dichotic listening and simple reaction time task with and without warnings. In the simple reaction time task, blocks of 80 stimuli were presented to each ear with and without warning cue under drug and placebo conditions. On the dichotic listening task the expected right ear advantage for reporting digits was obtained. While the drug had no main effect on the number of errors, there were more trials on which an ear advantage was present than in the placebo condition. In the reaction time task there were main effects of drug, warning cue and foreperiod: warnings facilitated reaction; chlorpromazine retarded reaction; and reaction times were most facilitated by warning foreperiods in excess of 1200ms. Several findings were of interest: On uncued trials, with placebo, right ear responses were faster than those for stimuli presented to the left ear. Drug also interacted with foreperiod duration. These results were interpreted in the light of Tucker and Williamson’s (1984) review of the role of Pribram and McGuinness’s Arousal and Activation sytems in lateralized behavior.