Auditory Lateralization Research Articles

Multiple Sclerosis: Left Advantage for Auditory Laterality in Dichotic Tests of Central Auditory Processing and Relationship of Psychoacoustic Tests With the Multiple Sclerosis Disability Scale-EDSS

ObjectiveTo evaluate the central auditory processing disorders in patients with multiple sclerosis, emphasizing auditory laterality by applying psychoacoustic tests and to identify their relationship with the Multiple Sclerosis Disability Scale (EDSS) functions. MethodDepression scales (HADS), EDSS, and 9 psychoacoustic tests to study CAPD were applied to 26 individuals with multiple sclerosis and 26 controls. Correlation tests were performed between the EDSS and psychoacoustic tests. ResultsSeven out of 9 psychoacoustic tests were significantly different (P<.05); right or left (14/19 explorations) with respect to control. In dichotic digits there was a left-ear advantage compared to the usual predominance of RDD. There was significant correlation in five psychoacoustic tests and the specific functions of EDSS. ConclusionThe left-ear advantage detected and interpreted as an expression of deficient influences of the corpus callosum and attention in multiple sclerosis should be investigated. There was a correlation between psychoacoustic tests and specific EDSS functions.

Binaural sensitivity to temporal fine structure and lateralization ability in children with suspected (central) auditory processing disorder

ObjectivePrevious studies have shown that a subgroup of children with suspected (central) auditory processing disorder (SusCAPD) have insufficient ability to use binaural cues to benefit from spatial processing. Thus, they experience considerable listening difficulties in challenging auditory environments, such as classrooms. Some researchers have also indicated the probable role of binaural temporal fine structure (TFS) in the perceptual segregation of target signal from noise and hence in speech perception in noise. Therefore, in the present study, in order to further investigate the underlying reason for listening problems against background noise in this group of children, their performance was measured using binaural TFS sensitivity test (TFS-LF) as well as behavioral auditory lateralization in noise test, both of which are based on binaural temporal cues processing. MethodsParticipants in this analytical study included 91 children with normal hearing and no listening problems and 41 children (9–12 years old) with SusCAPD who found it challenging to understand speech in noise. Initially, the ability to use binaural TFS was measured at three frequencies (250, 500 and 750Hz) in both the groups, and the results of preliminary evaluations were compared between normal children and those with SusCAPD who participated in the study. Thereafter, the binaural performance of the 16 children with SusCAPD who had higher thresholds than the normal group at all three frequencies tested in TFS-LF test was examined using the lateralization test in 7 spatial locations. ResultsTotal 16 of the 41 children with SusCAPD who participated in this study (39%) showed poor performance on the TFS-LF test at all three frequencies, compared to both normal children and other children in the APD group (p<0.05). Furthermore, children in the APD group with binaural TFS coding deficits at all three frequencies revealed significant differences in the lateralization test results compared to normal children (p<0.05). ConclusionFindings of the current study demonstrated that one of the underlying causes for the difficulty understanding speech in noisy environments experienced by a subgroup of children with SusCAPD can be the reduced ability to benefit from binaural TFS information. This study also showed that a reduced ability to use binaural TFS cues in the group of children with SusCAPD was accompanied by reduced binaural processing abilities in the lateralization test which also admit the presence of binaural temporal processing deficits in this group of children.

Esclerosis múltiple: ventaja izquierda para la lateralidad auditiva en pruebas dicóticas de procesamiento auditivo central y relación de pruebas psicoacústicas con examen de discapacidad-EDEM

ObjectiveTo evaluate the central auditory processing disorders in patients with multiple sclerosis, emphasizing auditory laterality by applying psychoacoustic tests and to identify their relationship with the Multiple Sclerosis Disability Scale (EDSS) functions. MethodDepression scales (HADS), EDSS, and 9 psychoacoustic tests to study CAPD were applied to 26 individuals with multiple sclerosis and 26 controls. Correlation tests were performed between the EDSS and psychoacoustic tests. ResultsSeven out of 9 psychoacoustic tests were significantly different (P<.05); right or left (14/19 explorations) with respect to control. In dichotic digits there was a left-ear advantage compared to the usual predominance of RDD. There was significant correlation in five psychoacoustic tests and the specific functions of EDSS. ConclusionThe left-ear advantage detected and interpreted as an expression of deficient influences of the corpus callosum and attention in multiple sclerosis should be investigated. There was a correlation between psychoacoustic tests and specific EDSS functions.

Auditory Lateralization Training Effects on Binaural Interaction Component of Middle Latency Response in Children Suspected to Central Auditory Processing Disorder.

Many children with central auditory processing disorder (C)APD suffer from spatial processing disorder and benefit from binaural processing training including auditory lateralization training. There are subjective tests for evaluating auditory training effects in children with (C)APD but they rely on patient's attention and cooperation so there is a need for appropriate objective tests. The aim of present study was investigating effects of auditory lateralization training on binaural interaction component (BIC) of middle latency response (MLR). This study was an analytical interventional study. Sixty children suspected to (C)APD (40 boys and 20 girls) were selected based on inclusion criteria and were divided into two groups: control and training group. Auditory lateralization training included 12 formal sessions under headphone by using interaural time difference and performed as a game. MLR (monaural right ear, monaural left ear and binaural) and monaural selective auditory attention test (mSAAT) tests were performed in all the cases. BIC was calculated by subtracting binaural response from summed monaural responses. Covariance test showed that BIC latency decreased and BIC amplitude increased significantly and mSAAT score increased significantly in training group after auditory lateralization training (p value ≤0.001). In present study BIC of MLR had potential to show underlying neurophysiologic changes after auditory lateralization training in children suspected to (C)APD objectively. It is in agreement with behavioral improvements after training (mSAAT improvements).

Neuropsychological parameters as possible indicators of speech fluency disorder in children

Background/Aim. Speech disfluency (stuttering) is a multifactor disorder and its aetiology is a big unknown for the experts from various fields. Hemisphere dominance as the highest level in the process of integration of cortical functions is of special significance for the entire development. Praxis and gnosis related cortical organizers are the first to form; they become differentiated and functionally full in early childhood while the process of condensing is completed somewhere around the age of 7. Cortical activity organizers are definitely set at that age and from then on act from one hemisphere which becomes dominant for that function. Laterality is determined by hemisphere dominance, but it occurs as a special phenomenon and it is of great significance for personality. The aim of this research was to examine the influence and the relationship between hemisphere asymmetry on the occurrence of speech disfluency in children. Methods. Sixty children aged 5 to 7 years participated in this research. Thirty children suffer from speech fluency disorder (person who stutters ? PWS) and they belong to the experimental group while thirty children are fluent speakers (person who does not stutter ? PWNS) and they were the control group. Individual testing was used as a test method. Laterality assessment test was used as an instrument which consists of 5 sub-tests as follows: the assessment of hand-use laterality, the assessment of gestural handuse laterality, the assessment of foot laterality, the assessment of auditory laterality and the assessment of visual laterality. Results. Gestural hand-use laterality and auditory laterality in the PWS examinees were considerably worse in comparison to the PWNS examinees (?2 = 11.80, p = 0.002, and ?2 = 10.90, p = 0.003, respectively). Male examinees had worse scores in comparison with female examinees. Conclusion. There are certain changes in establishing a dominant hemisphere and differentiation of laterality in children who stutter in comparison with the children who are fluent speakers, which has been shown by statistically significant difference in accomplishments at the test of gestural hand-use laterality and the test of auditory laterality.

The head turn paradigm to assess auditory laterality in cats: influence of ear position and repeated sound presentation.

In most humans, speech is predominantly processed by the left hemisphere. This auditory laterality was formerly thought to be an exclusive human characteristic, but is now suggested to have pre-human origins. In studies on auditory laterality in nonhuman animals, the head turn paradigm has become very popular due to its non-invasive character. Although there are implications that the head turn direction indicates functional dominance of the contralateral hemisphere in processing a given sound, the validity of the paradigm is under debate. To validate the paradigm via comparison with imaging or electrophysiological methods, it is first necessary to establish turning biases at the individual level. Recently, the domestic cat, a common model in hearing research, has been found to show turning biases at the group level. To assess individual turning asymmetries in cats, we repeatedly presented kitten isolation calls and assessed whether differences in conveyed arousal changed the previously described left-wards lateralisation of conspecific vocalizations. Based on responses to 50 playback presentations (25 of high and 25 of low arousal), we calculated individual head turn indices. Based on the total data set, we found no consistent individual turning bias, irrespective of call category or sex of the receiver. Although the playback paradigm was chosen carefully to reduce any effects of lateralized loudness perception or changes in motivation due to habituation, individual head turn biases changed significantly in concordance with habituation to repeated playback-presentations and was predictable by small deflections in ear position prior to listening. When splitting the data set according to a decline in responsiveness after seven playback presentations, we revealed an initial left turning bias for most of our subjects (i.e., significant at the group level). We propose that this left turning bias is related to right hemisphere dominance in processes like vigilance behaviour or general arousal rather than on auditory processing, as such. Our findings suggest that both the experimental sequence and sound level differences, induced by asymmetric ear positions, strongly influence the outcome of the head turn paradigm and should be taken into account when evaluating auditory laterality at the behavioural level.

Right-ear precedence and vocal emotion contagion: The role of the left hemisphere

ABSTRACTMuch evidence suggests that the processing of emotions is lateralized to the right hemisphere of the brain. However, under some circumstances the left hemisphere might play a role, particularly for positive emotions and emotional experiences. We explored whether emotion contagion was right-lateralized, lateralized valence-specifically, or potentially left-lateralized. In two experiments, right-handed female listeners rated to what extent emotionally intoned pseudo-sentences evoked target emotions in them. These sound stimuli had a 7 ms ear lead in the left or right channel, leading to stronger stimulation of the contralateral hemisphere. In both experiments, the results revealed that right ear lead stimuli received subtly but significantly higher evocation scores, suggesting a left hemisphere dominance for emotion contagion. A control experiment using an emotion identification task showed no effect of ear lead. The findings are discussed in relation to prior findings that have linked the processing of emotional prosody to left-hemisphere brain regions that regulate emotions, control orofacial musculature, are involved in affective empathy processing areas, or have an affinity for processing emotions socially. Future work is needed to eliminate alternative interpretations and understand the mechanisms involved. Our novel binaural asynchrony method may be useful in future work in auditory laterality.

Audition and Hemispheric Specialization in Songbirds and New Evidence from Australian Magpies

The neural processes of bird song and song development have become a model for research relevant to human acquisition of language, but in fact, very few avian species have been tested for lateralization of the way in which their audio-vocal system is engaged in perception, motor output and cognition. Moreover, the models that have been developed have been premised on birds with strong vocal dimorphism, with a tendency to species with complex social and/or monomorphic song systems. The Australian magpie (Gymnorhina tibicen) is an excellent model for the study of communication and vocal plasticity with a sophisticated behavioural repertoire, and some of its expression depends on functional asymmetry. This paper summarizes research on vocal mechanisms and presents field-work results of behavior in the Australian magpie. For the first time, evidence is presented and discussed about lateralized behaviour in one of the foremost songbirds in response to specific and specialized auditory and visual experiences under natural conditions. It presents the first example of auditory lateralization evident in the birds’ natural environment by describing an extractive foraging event that has not been described previously in any avian species. It also discusses the first example of auditory behavioral asymmetry in a songbird tested under natural conditions.

Effect of voicing on perceptual auditory laterality in Estonian and Norwegian native speakers

ABSTRACTAs a reliable and valid measures of perceptual auditory laterality, dichotic listening has been successfully applied in studies in many countries and languages. However, languages differ in the linguistic relevance of change in initial phoneme of words (e.g., for word identification). In the present cross-language study, we examine the effect of these differences on dichotic-listening task performance to establish how characteristics of one's native language affect the perception of nonnative phonological features. We compared 33 native speakers of Norwegian, a language characterized by a clear distinction between voiced and unvoiced initial plosive consonants, with 30 native speakers of Estonian, a language that has exclusively unvoiced initial phonemes. Using a free-report dichotic-listening paradigm utilizing pairs of voiced (/ba/, /da/, /ga/) and unvoiced (/pa/, /ta/, /ka/) stop-consonant vowels as stimulus material, the Norwegian native speakers were found to be more sensitive to the voicing of the initial plosive than the Estonian group. “Voicing” explained 69% and 18% of the variance in the perceptual auditory laterality in the Norwegian and the Estonian sample, respectively. This indicates that experiential differences, likely during acquisition of the mother tongue in early development, permanently shape the sensitivity to the voicing contrast.

Brain Functional Asymmetry of Chimpanzees (Pan troglodytes): the Example of Auditory Laterality

Abstract The aim of this study was to verify whether chimpanzees (Pan troglodytes) demonstrate an auditory laterality during the orientation reaction, and which hemisphere is responsible for processing the emotional stimuli and which for the species-specific vocalizations. The study involved nine chimpanzees from the Warsaw Municipal Zoological Garden. They were tested individually in their bedrooms. Chimpanzees approached a tube filled with food, located in the centre of the cage. Randomly selected sounds were played from the speakers when the subject was focused on getting food. Individual reactions were observed and outcomes reported. The four types of sound used: thunderstorm, dog barking, chimpanzee vocalization and a zookeeper’s voice. To test whether chimpanzees demonstrate auditory laterality we used a single sample X2 test. The existence of auditory laterality has been confirmed. The sound of the storm caused the orientation reaction to the left, while chimpanzee vocalization - to the right. On this basis we can conclude that among chimpanzees, arousing stimuli are being processed by the right hemisphere, and species-specific vocalizations by the left. However, the set of stimuli was limited so the study did not unequivocally resolve this issue.

Infant Cortical Auditory Evoked Potentials to Lateralized Noise Shifts Produced by Changes in Interaural Time Difference.

Newborns reliably orient to sound location soon after birth; by age 1 month this orienting disappears until after age 4 months. It has been suggested that orienting by the newborn reflects subcortical-mediated reflexes, which are suppressed by age 1 month; reappearance of orienting then occurs after age 4 months with maturation of cortical mechanisms of sound localization. In the present study, we assess auditory lateralization in young infants (and adults) by recording slow cortical auditory evoked potentials to lateralization shifts in dichotic noise produced by changes in interaural time difference (ITD). Fifteen normal infants aged under 4 months (mean = 10.7 weeks) had cortical auditory evoked potentials assessed in response to (1) diotic "onset" noise bursts (0 msec ITD) and (2) shifts in continuous lateralized noise (75 dB SPL) produced by ITD shifts of 0.5, 0.8, 1, 2, 4, and 8 msec. Shifts alternated between ears occurred every 2 sec. Stimuli were presented using insert earphones; infants slept during recordings. For comparison, similar recordings were obtained in 11 normal-hearing, awake, adults. Additionally, "control" recordings to the ITD-shift stimuli presented to only one ear were obtained in the adults. Similar to previous research, adults showed clear N1-P2 responses to the lateralization shifts (ITD 0.5 to 2.0 msec). Responses decreased for longer ITD shifts, with no adult responses to the 8-msec ITD shift. N1 latencies to ITD-shift stimuli were 28 to 34 msec longer than to the onset stimuli. No responses were seen in the control conditions when ITD-shift stimuli were presented to only one ear (confirming the binaural nature of the ITD-shift responses). All infants showed P2 responses to one or more of the ITD-shift stimuli up to ±1 msec; compared with adults, infants showed larger amplitude decreases and fewer responses to longer ITD-shift stimuli. As was seen with the adult responses, infant response (P2) latencies to ITD shifts were longer compared with their responses to the onset stimuli; however, these increases, 32 to 78 msec, were significantly longer than those seen in the adults. Young infants (even as young as 5 weeks) show clear evidence of auditory cortical responsivity to lateralization shifts produced by changes in the ITD of continuous noise, indicating that they have the capacity to process binaural ITD timing cues well before the age of 4 months. Further research is required to determine whether the larger latency increase in infants for ITD-shift stimuli (relative to the onset stimuli) and the greater effect of longer ITD shifts on response presence and amplitude in infants reflects immaturity of lateralization processing and/or reduced responses recorded during sleep. Slow cortical auditory evoked potentials elicited to lateralization shifts in dichotic noise provide a method to investigate binaural hearing processes in young children with normal or impaired hearing.

Opposite brain laterality in analogous auditory and visual tests

ABSTRACTLaterality for language processing can be assessed by auditory and visual tasks. Typically, a right ear/right visual half-field (VHF) advantage is observed, reflecting left-hemispheric lateralization for language. Historically, auditory tasks have shown more consistent and reliable results when compared to VHF tasks. While few studies have compared analogous tasks applied to both sensory modalities for the same participants, one such study by Voyer and Boudreau [(2003). Cross-modal correlation of auditory and visual language laterality tasks: a serendipitous finding. Brain Cogn, 53(2), 393–397] found opposite laterality for visual and auditory language tasks. We adapted an experimental paradigm based on a dichotic listening and VHF approach, and applied the combined language paradigm in two separate experiments, including fMRI in the second experiment to measure brain activation in addition to behavioural data. The first experiment showed a right-ear advantage for the auditory task, but a left half-field advantage for the visual task. The second experiment, confirmed the findings, with opposite laterality effects for the visual and auditory tasks. In conclusion, we replicate the finding by Voyer and Boudreau (2003) and support their interpretation that these visual and auditory language tasks measure different cognitive processes.

A comparison of the brainstem auditory evoked response in healthy ears of unilaterally deaf dogs and bilaterally hearing dogs

AimsAuditory plasticity in response to unilateral deafness has been reported in various animal species. Subcortical changes occurring in unilaterally deaf young dogs using the brainstem auditory evoked response have not been evaluated yet. The aim of this study was to assess the brainstem auditory evoked response findings in dogs with unilateral hearing loss, and compare them with recordings obtained from healthy dogs.MethodsBrainstem auditory evoked responses (amplitudes and latencies of waves I, II, III, V, the V/I wave amplitude ratio, wave I-V, I-III and III-V interpeak intervals) were studied retrospectively in forty-six privately owned dogs, which were either unilaterally deaf or had bilateral hearing. The data obtained from the hearing ears in unilaterally deaf dogs were compared to values obtained from their healthy littermates.ResultsStatistically significant differences in the amplitude of wave III and the V/I wave amplitude ratio at 75 dB nHL were found between the group of unilaterally deaf puppies and the control group. The recordings of dogs with single-sided deafness were compared, and the results showed no statistically significant differences in the latencies and amplitudes of the waves between left- (AL) and right-sided (AR) deafness.ConclusionsThe recordings of the brainstem auditory evoked response in canines with unilateral inborn deafness in this study varied compared to recordings from healthy dogs. Future studies looking into electrophysiological assessment of hearing in conjunction with imaging modalities to determine subcortical auditory plasticity and auditory lateralization in unilaterally deaf dogs are warranted.

Effects of an Auditory Lateralization Training in Children Suspected to Central Auditory Processing Disorder.

Background and ObjectivesCentral auditory processing disorder [(C)APD] refers to a deficit in auditory stimuli processing in nervous system that is not due to higher-order language or cognitive factors. One of the problems in children with (C)APD is spatial difficulties which have been overlooked despite their significance. Localization is an auditory ability to detect sound sources in space and can help to differentiate between the desired speech from other simultaneous sound sources. Aim of this research was investigating effects of an auditory lateralization training on speech perception in presence of noise/competing signals in children suspected to (C)APD.Subjects and MethodsIn this analytical interventional study, 60 children suspected to (C)APD were selected based on multiple auditory processing assessment subtests. They were randomly divided into two groups: control (mean age 9.07) and training groups (mean age 9.00). Training program consisted of detection and pointing to sound sources delivered with interaural time differences under headphones for 12 formal sessions (6 weeks). Spatial word recognition score (WRS) and monaural selective auditory attention test (mSAAT) were used to follow the auditory lateralization training effects.ResultsThis study showed that in the training group, mSAAT score and spatial WRS in noise (p value≤0.001) improved significantly after the auditory lateralization training.ConclusionsWe used auditory lateralization training for 6 weeks and showed that auditory lateralization can improve speech understanding in noise significantly. The generalization of this results needs further researches.

Auditory lateralization of conspecific and heterospecific vocalizations in cats

ABSTRACTAuditory lateralization in response to both conspecific and heterospecific vocalizations (dog vocalizations) was observed in 16 tabby cats (Felis catus). Six different vocalizations were used: cat “purring,” “meowing” and “growling” and dog typical vocalizations of “disturbance,” “isolation” and “play.” The head-orienting paradigm showed that cats turned their head with the right ear leading (left hemisphere activation) in response to their typical-species vocalization (“meow” and “purring”); on the other hand, a clear bias in the use of the left ear (right hemisphere activation) was observed in response to vocalizations eliciting intense emotion (dogs’ vocalizations of “disturbance” and “isolation”). Overall these findings suggest that auditory sensory domain seems to be lateralized also in cat species, stressing the role of the left hemisphere for intraspecific communication and of the right hemisphere in processing threatening and alarming stimuli.

Dichotic listening and attention: the legacy of Phil Bryden

ABSTRACTIn this article I review the early auditory laterality and dichotic listening research from the perspective of the legacy of Phil Bryden's pioneering contributions to not only empirical work, but also on theory, critical interpretations of results, and statistical issues, with a focus on the role of attention. In doing so, I am describing how my own research was shaped and influenced by Phil Bryden and his work on auditory laterality and dichotic listening. In addition to personal recollections of my meetings and discussions with Phil that had a profound impact on my later career, I have focused the overview on Phil's early dichotic listening papers from the 1960s, to be followed by a detailed review and discussion of the seminal [Bryden, M. P., Munhall, K., & Allard, F. (1983). Attentional biases and the right-ear effect in dichotic listening. Brain and Language, 18, 236–248] paper on attentional effects on the ear advantage in dichotic listening. Finally, I review the little known fact that Phil was also a contributor to the very first functional neuroimaging study that used dichotic stimuli.

Laterality, spatial abilities, and accident proneness

Although handedness as a measure of cerebral specialization has been linked to accident proneness, more direct measures of laterality are rarely considered. The present study aimed to fill that gap in the existing research. In addition, individual difference factors in accident proneness were further examined with the inclusion of mental rotation and navigation abilities measures. One hundred and forty participants were asked to complete the Mental Rotations Test, the Santa Barbara Sense of Direction scale, the Greyscales task, the Fused Dichotic Word Test, the Waterloo Handedness Questionnaire, and a grip strength task before answering questions related to number of accidents in five areas. Results indicated that handedness scores, absolute visual laterality score, absolute response time on the auditory laterality index, and navigation ability were significant predictors of the total number of accidents. Results are discussed with respect to cerebral hemispheric specialization and risk-taking attitudes and behavior.

Lateralization and cognitive systems.

Lateralization and cognitive systems.

The relation between working memory capacity and auditory lateralization in children with auditory processing disorders

ObjectiveAuditory processing disorder (APD) describes a complex and heterogeneous disorder characterized by poor speech perception, especially in noisy environments. APD may be responsible for a range of sensory processing deficits associated with learning difficulties. There is no general consensus about the nature of APD and how the disorder should be assessed or managed. This study assessed the effect of cognition abilities (working memory capacity) on sound lateralization in children with auditory processing disorders, in order to determine how “auditory cognition” interacts with APD. MethodsThe participants in this cross-sectional comparative study were 20 typically developing and 17 children with a diagnosed auditory processing disorder (9–11 years old). Sound lateralization abilities investigated using inter-aural time (ITD) differences and inter-aural intensity (IID) differences with two stimuli (high pass and low pass noise) in nine perceived positions. Working memory capacity was evaluated using the non-word repetition, and forward and backward digits span tasks. Linear regression was employed to measure the degree of association between working memory capacity and localization tests between the two groups. ResultsChildren in the APD group had consistently lower scores than typically developing subjects in lateralization and working memory capacity measures. The results showed working memory capacity had significantly negative correlation with ITD errors especially with high pass noise stimulus but not with IID errors in APD children. ConclusionsThe study highlights the impact of working memory capacity on auditory lateralization. The finding of this research indicates that the extent to which working memory influences auditory processing depend on the type of auditory processing and the nature of stimulus/listening situation.

Mapping hemispheric symmetries, relative asymmetries, and absolute asymmetries underlying the auditory laterality effect

Functional hemispheric differences for speech and language processing have been traditionally studied by using verbal dichotic-listening paradigms. The commonly observed right-ear preference for the report of dichotically presented syllables is taken to reflect the left hemispheric dominance for speech processing. However, the results of recent functional imaging studies also show that both hemispheres – not only the left – are engaged by dichotic listening, suggesting a more complex relationship between behavioral laterality and functional hemispheric activation asymmetries. In order to more closely examine the hemispheric differences underlying dichotic-listening performance, we report an analysis of functional magnetic resonance imaging (fMRI) data of 104 right-handed subjects, for the first time combining an interhemispheric difference and conjunction analysis. This approach allowed for a distinction of homotopic brain regions which showed symmetrical (i.e., brain region significantly activated in both hemispheres and no activation difference between the hemispheres), relative asymmetrical (i.e., activated in both hemispheres but significantly stronger in one than the other hemisphere), and absolute asymmetrical activation patterns (i.e., activated only in one hemisphere and this activation is significantly stronger than in the other hemisphere). Symmetrical activation was found in large clusters encompassing temporal, parietal, inferior frontal, and medial superior frontal regions. Relative and absolute left-ward asymmetries were found in the posterior superior temporal gyrus, located adjacent to symmetrically activated areas, and creating a lateral–medial gradient from symmetrical towards absolute asymmetrical activation within the peri-Sylvian region. Absolute leftward asymmetry was also found in the post-central and medial superior frontal gyri, while rightward asymmetries were found in middle temporal and middle frontal gyri. We conclude that dichotic listening engages a bihemispheric cortical network, showing a symmetrical and mostly leftward asymmetrical pattern. The here obtained functional (a)symmetry map might serve as a basis for future studies which – by studying the relevance of the here identified regions – clarify the relationship between behavioral laterality measures and hemispheric asymmetry.