Left Hemisphere Advantage Research Articles

Speech-Processing Network Formation of Cochlear-Implanted Toddlers With Early Hearing Experiences.

To reveal the formation process of speech processing with early hearing experiences, we tracked the development of functional connectivity in the auditory and language-related cortical areas of 84 (36 female) congenitally deafened toddlers using repeated functional near-infrared spectroscopy for up to 36 months post cochlear implantation (CI). Upon hearing restoration, the CI children lacked the modular organization of the mature speech-processing network and demonstrated a higher degree of immaturity in temporo-parietal than temporo-frontal connections. The speech-processing network appeared to form rapidly with early CI experiences, with two-thirds of the developing connections following nonlinear trajectories reflecting possibly more than one synaptogenesis-pruning cycle. A few key features of the mature speech-processing network emerged within the first year of CI hearing, including left-hemispheric advantage, differentiation of the dorsal and ventral processing streams, and functional state (speech listening vs. resting) specific patterns of connectivity development. The developmental changes were predictable of future auditory and verbal communication skills of the CI children, with prominent contribution from temporo-parietal connections in the dorsal stream, suggesting a mediating role of speech-processing network formation with early hearing experiences in speech acquisition.

Left or right, that is the question: use of egocentric frame of reference and the right-eye advantage for understanding gestural signs in bottlenose dolphins (Tursiops truncates).

How do bottlenose dolphins visually perceive the space around them? In particular, what cues do they use as a frame of reference for left-right perception? To address this question, we examined the dolphin's responses to various manipulations of the spatial relationship between the dolphin and the trainer by using gestural signs for actions given by the trainer, which have different meanings in the left and right hands. When the dolphins were tested with their backs to the trainer (Experiment 1) or in an inverted position underwater (Experiments 2 and 3), correct responses from the trainer's perspective were maintained for signs related to movement direction instructions. In contrast, reversed responses were frequently observed for signs that required different sounds for the left and right hands. When the movement direction instructions were presented with symmetrical graphic signs such as " × " and "●", accuracy decreased in the inverted posture (Experiment 3). Furthermore, when the signs for sounds were presented from either the left or right side of the dolphin's body, performance was better when the side of the sign movement coincided with the body side on which it was presented than when it was mismatched (Experiment 4). In the final experiment, when one eye was covered with an eyecup, the results showed that, as in the case of body-side presentation, performance was better when the open eye coincided with the side on which the sign movement was presented. These results indicate that dolphins used the egocentric frame for visuospatial cognition. In addition, they showed better performances when the gestural signs were presented to the right eye, suggesting the possibility of a left-hemispheric advantage in the dolphin's visuospatial cognition.

Hemispheric involvement in the comprehension of conventional metaphors in Arabic–Hebrew speakers

Aims and objectives/purpose/research questions: Previous studies in pairs of typologically distant languages showed that hemispheric processing of metaphoric expressions differs in a native versus second language. The current research explored this finding in a pair of typologically close languages, Arabic and Hebrew. Design/methodology/approach: Forty-six Arabic native speakers who were proficient in Hebrew (second language; 30 women, aged 19–28) participated in a divided visual field (DVF) experiment. They were presented with conventional metaphors, literal expressions, and unrelated word pairs and asked to indicate whether the word pairs formed a meaningful expression. Participants were tested in spoken Arabic, literary Arabic, and Hebrew in separate blocks. Data and analysis: Mean reaction times and accuracy were analyzed using repeated-measures three-way analysis of variance, with language, visual field, and expression type as independent variables. Findings/conclusions: In contrast to previously reported findings, a left-hemisphere advantage or a bilateral pattern of processing was observed for conventional metaphors in both varieties of Arabic and in Hebrew, suggesting similar hemispheric processing in native and second language. Originality: Metaphor processing is examined in a pair of typologically close languages. Significance/implications: Our findings (in a pair of typologically close languages) differ from those previously reported in pairs of less similar languages, suggesting a modulatory role of language similarity in hemispheric processing of second-language metaphors.

Task-domain and hemisphere-asymmetry effects in cisgender and transmale individuals.

The present research examined the extent to which transmale individuals’ functional brain organization resembles that of their assigned sex or gender identity. Cisgender-female, cisgender-male, and transmale participants, who were assigned female sex but did not have a female gender identity, were compared in terms of effects that have been observed in cisgender individuals: task-domain effects, in which males perform better than females on spatial tasks and females perform better than males on verbal tasks; and hemisphere-asymmetry effects, in which males show larger differences between the left and right hemispheres than females. In addition, the present research measured participants’ intelligence in order to control for potential moderating effects. Participants performed spatial (mental rotation) and verbal (lexical decision) tasks presented to each hemisphere using a divided-visual field paradigm, and then completed an intelligence assessment. In the mental-rotation task, cismale and transmale participants performed better than cisfemale participants, however this group difference was explained by intelligence scores, with higher scores predicting better performance. In the lexical-decision task, cismale and transmale participants exhibited a greater left-hemisphere advantage than cisfemales, and this difference was not affected by intelligence scores. Taken together, results do not support task-domain effects when intelligence is accounted for; however, they do demonstrate a hemisphere-asymmetry effect in the verbal domain that is moderated by gender identity and not assigned sex.

Visual lateralization in flight: Lateral preferences in parent‐offspring relative positions in geese

AbstractVisual lateralization arises from the differential processing of information by the two brain hemispheres and can manifest itself in animal behaviour in the form of lateral preferences. Current evidence suggests that social coordination serves as a driving force for the emergence of one‐sided behavioural preferences in the populations. Collective movement is one of the most basic and ubiquitous examples of coordinated behaviour. Very little is known, however, about lateralized social interactions in such a complex and sensory demanding movement mode as flight. In the present study, we aimed at investigating lateralization in parent‐offspring interactions during migratory and nonmigratory flights in greater white‐fronted geese. Analyzing the GPS tracks of 19 goose families, we showed individual lateral preferences in the position of juvenile birds relative to a parent in nearly half of the juveniles. A population‐level preference to follow the mother on her left side was shown in juveniles during migratory flights but not in other analyses. This preference, differently from previous findings in mammals implicating a right eye bias, may be explained by the left hemisphere advantage for the functions involved in following behaviour of migrating birds, e.g., focussed attention. This highlights different drivers of lateralization in collective movement in relation to situation‐specific demands.

Left Hemisphere Dominance for Negative Facial Expressions: The Influence of Task.

Major theories of hemisphere asymmetries in facial expression processing predict right hemisphere dominance for negative facial expressions of disgust, fear, and sadness, however, some studies observe left hemisphere dominance for one or more of these expressions. Research suggests that tasks requiring the identification of six basic emotional facial expressions (angry, disgusted, fearful, happy, sad, and surprised) are more likely to produce left hemisphere involvement than tasks that do not require expression identification. The present research investigated this possibility in two experiments that presented six basic emotional facial expressions to the right or left hemisphere using a divided-visual field paradigm. In Experiment 1, participants identified emotional expressions by pushing a key corresponding to one of six labels. In Experiment 2, participants detected emotional expressions by pushing a key corresponding to whether an expression was emotional or not. In line with predictions, fearful facial expressions exhibited a left hemisphere advantage during the identification task but not during the detection task. In contrast to predictions, sad expressions exhibited a left hemisphere advantage during both identification and detection tasks. In addition, happy facial expressions exhibited a left hemisphere advantage during the detection task but not during the identification task. Only angry facial expressions exhibited a right hemisphere advantage, and this was only observed when data from both experiments were combined. Together, results highlight the influence of task demands on hemisphere asymmetries in facial expression processing and suggest a greater role for the left hemisphere in negative expressions than predicted by previous theories.

Hemispheric Asymmetry in Visual Processing: An ERP Study on Spatial Frequency Gratings

A hemispheric asymmetry for the processing of global versus local visual information is known. In this study, we investigated the existence of a hemispheric asymmetry for the visual processing of low versus high spatial frequency gratings. The event-related potentials were recorded in a group of healthy right-handed volunteers from 30 scalp sites. Six types of stimuli (1.5, 3 and 6 c/deg gratings) were randomly flashed 180 times in the left and right upper hemifields. The stimulus duration was 80 ms, and the interstimulus interval (ISI) ranged between 850 and 1000 ms. Participants paid attention and responded to targets based on their spatial frequency and location. The C1 and P1 visual responses, as well as a later selection negativity and a P300 component of event-related potentials (ERPs), were quantified and subjected to repeated-measure analyses of variance (ANOVAs). Overall, the performance was faster for the right visual field (RVF), thus suggesting a left hemispheric advantage for the attentional selection of local elements. Similarly, the analysis of the mean area amplitude of the C1 (60–110 ms) sensory response showed a stronger attentional effect (F+L+ vs. F−L+) at the left occipital areas, thus suggesting the sensory nature of this hemispheric asymmetry.

Right visual field advantage for lexical decision dependent on stimulus size and visibility: Evidence for an early processing account of hemispheric asymmetry

ABSTRACT Previous research suggests that the right visual field advantage on the lexical decision task occurs independent of the visual quality of stimuli [Chiarello, C., Senehi, J., & Soulier, M. (1986). Viewing conditions and hemisphere asymmetry for the lexical decision. Neuropsychologia, 24(4), 521–529]. However, previous studies examining these effects have had methodological limitations that were addressed and controlled for in the present study. Participants performed a divided visual field, lexical decision task for words that varied in size (Experiment 1) and visibility (Experiment 2). Results showed a quality by visual field interaction effect. In both experiments, response times were faster for targets presented to the right visual field in the high quality (i.e., large font, high visibility) conditions; however, visual quality resulted in no differences for targets presented to the left visual field. Furthermore, this quality by visual field interaction effect was only observed when the target was a word. These results suggest that the left hemisphere advantage for lexical decision depends on the perceptual quality of targets, consistent with an early stage of processing account of hemispheric asymmetry during lexical decision. Findings are discussed within the context of word recognition and decision-based models.

Hemispheric processing of predictive inferences: the effects of textual constraint and metacomprehension monitoring competence

Previous research into predictive inferences making showed that textual constraint influenced hemispheric processing of the inferences. However, the relationship between metacomprehension monitoring competence (MMC) and hemispheric processing of predictive inferences has rarely been investigated. The present study employed a divided visual field (DVF) paradigm to examine the effects of textual constraint and MMC on hemispheric processing of predictive inferences with Chinese native speakers during Chinese text reading. Results showed that neither response time nor facilitation effects indicated any significant interaction for our MMC groups. MMC was unlikely to play a role in hemispheric processing of predictive inferences. The results were consistent with those of the very rare relevant previous research, in which readers’ judgments of learning failed to have significant effects on inference making performance while judgments of inferencing had. Future investigation could focus more on the study of an inference-specific dimension of metacomprehension monitoring that might be more closely related to inference making. Results also indicated that the left hemisphere (LH) showed greater facilitation for strongly constrained predictive inferences than for weakly constrained predictive inferences, and that the right hemisphere (RH) showed greater levels of facilitation for weakly constrained predictive inferences. Taken together, MMC did not seem to have a positive impact on hemispheric predictive inference making. There was a RH facilitation advantage for weakly constrained texts and an LH advantage for strongly constrained texts.

Hemispheric asymmetries in processing numerical meaning in arithmetic

Hemispheric asymmetries in arithmetic have been hypothesized based on neuropsychological, developmental, and neuroimaging work. However, it has been challenging to separate asymmetries related to arithmetic specifically, from those associated general cognitive or linguistic processes. Here we attempt to experimentally isolate the processing of numerical meaning in arithmetic problems from language and memory retrieval by employing novel non-symbolic addition problems, where participants estimated the sum of two dot arrays and judged whether a probe dot array was the correct sum of the first two arrays. Furthermore, we experimentally manipulated which hemisphere receive the probe array first using a visual half-field paradigm while recording event-related potentials (ERP). We find that neural sensitivity to numerical meaning in arithmetic arises under left but not right visual field presentation during early and middle portions of the late positive complex (LPC, 400-800 ms). Furthermore, we find that subsequent accuracy for judgements of whether the probe is the correct sum is better under right visual field presentation than left, suggesting a left hemisphere advantage for integrating information for categorization or decision making related to arithmetic. Finally, neural signatures of operational momentum, or differential sensitivity to whether the probe was greater or less than the sum, occurred at a later portion of the LPC (800-1000 ms) and regardless of visual field of presentation, suggesting a temporal and functional dissociation between magnitude and ordinal processing in arithmetic. Together these results provide novel evidence for differences in timing and hemispheric lateralization for several cognitive processes involved in arithmetic thinking.

Incidence and Symptomatology of Vascular Crossed Aphasia in Bengali.

Crossed aphasia (CA) refers to aphasia following a right-hemispheric lesion in right-handed individuals. It has been suggested that the prevalence of CA differs with language, although its worldwide incidence, as reported by most studies, is less than 3%. To find the incidence of CA in the Bengali language. From 2016 to 2018, in a hospital located in a Bengali-speaking area of eastern India, 515 cases of first-ever stroke were documented, out of which 208 patients presented with aphasia (40.38%) according to their scores on the Bengali version of the Western Aphasia Battery. Among the patients with aphasia, 14 (6.73%; 8 men and 6 women) presented with CA. Of these, 10 were diagnosed with Broca aphasia and four with transcortical motor aphasia. No patient presented with Wernicke aphasia. The relatively high incidence of CA in our study suggests that bi-hemispheric language representation may be more prevalent in Bengali speakers than in speakers of other languages. The absence of crossed Wernicke aphasia in our study participants may represent a left-hemispheric advantage for receptive language abilities in Bengali speakers. Further studies are required to clarify whether idiosyncrasies in the Bengali language may be responsible for the differential brain representation of language seen in our study participants.

Left-Hemispheric Asymmetry for Object-Based Attention: an ERP Study.

It has been shown that selective attention enhances the activity in visual regions associated with stimulus processing. The left hemisphere seems to have a prominent role when non-spatial attention is directed towards specific stimulus features (e.g., color, spatial frequency). The present electrophysiological study investigated the time course and neural correlates of object-based attention, under the assumption of left-hemispheric asymmetry. Twenty-nine right-handed participants were presented with 3D graphic images representing the shapes of different object categories (wooden dummies, chairs, structures of cubes) which lacked detail. They were instructed to press a button in response to a target stimulus indicated at the beginning of each run. The perception of non-target stimuli elicited a larger anterior N2 component, which was likely associated with motor inhibition. Conversely, target selection resulted in an enhanced selection negativity (SN) response lateralized over the left occipito-temporal regions, followed by a larger centro-parietal P300 response. These potentials were interpreted as indexing attentional selection and categorization processes, respectively. The standardized weighted low-resolution electromagnetic tomography (swLORETA) source reconstruction showed the engagement of a fronto-temporo-limbic network underlying object-based visual attention. Overall, the SN scalp distribution and relative neural generators hinted at a left-hemispheric advantage for non-spatial object-based visual attention.

Distinct effect of early and late embryonic light-stimulation on chicks' lateralization

Embryonic light exposure affects similarly functional lateralization in fish and birds. While the light acts on an asymmetric habenular system during the first post fertilization hours in zebrafish, in the domestic chicks it shapes the thalamofugal visual pathway affecting the right retinal photoreceptors in the last stages before hatching. However, recent evidence has shown that also in chicks a precocial embryonic time window seems open to light action. Here we addressed the issue of whether the light effect is comparable in the early and late sensitive periods of chicks' embryonic development by testing birds coming from early (EL) and late (LL) light stimulated eggs compared to dark maintained eggs (DK) under different conditions of vision in a gravel-grain task. The perseveration of pecks directed to irrelevant elements revealed that in all chicks the right hemisphere was heavily attracted by the novel elements when tested with the left eye. When using the right eye, instead, only DK chicks attended repeatedly to distractors whereas LL and EL chicks showed a left hemisphere advantage for fine discrimination and sustained attention; conversely, when tested binocularly, LL chicks perseverated significantly more than both DK and EL chicks, likely compensating the distraction with the analysis carried out by both hemispheres. For the first time, we unveiled a fine graded difference between the light modulation exerted during the two time windows, adding evidence to the idea that genes and environmental factors interplay in several separate routes to the modulation of the neurodevelopment of cerebral lateralization in vertebrates.

Which is more prominent for fighter pilots under different flight task difficulties: Visual alert or verbal alert?

To explore the behavioural and cognition patterns of fighter pilots under visual and verbal alert conditions, 20 right-handed subjects participated in the experiment after 200 h of flight task training, and ERP technology was used to conduct EEG experiments under four conditions: high time pressure visual alert, low time pressure visual alert, fast speech speed verbal alert, and slow speech speed verbal alert. The results indicated the following: 1) the highest accuracy rate and shortest reaction time could be achieved under the slow speech speed verbal alert condition, indicating that the slow speech speed alert performance was optimal. 2) Subjects in the verbal alert trial showed a “right hemisphere advantage”, and the brain function area was located in the right temporal lobes. The speech speed correlated negatively with the latency and amplitude of P80.3) Subjects in the visual alert trial showed a “left hemisphere advantage”, and the brain activity was located in the left parietal lobes. 4) The latency of P80 evoked by verbal alert was earlier than that of N140 evoked by visual alert, indicating that a verbal alert causes an earlier attention effect in pilots. Based on the eye movement experiment, the performance of visual and verbal dual-channel alert was significantly higher than that of visual alert.

Right hemisphere involvement for pun processing – Effects of idiom decomposition

Abstract The present study investigated hemispheric processing of puns involving decomposable idioms (e.g. Old skiers never die, they just go downhill) and non-decomposable ones (e.g., Old cleaners never die, they just bite the dust) using a divided visual field paradigm. In two cross-modal priming experiments, participants listened to puns and made lexical decisions for targets presented either in the left or right visual fields. To investigate hemispheric asymmetries at different processing stages (early vs. late), the prime-target inter-stimulus interval was 0 ms in Experiment 1 and was increased to 750 ms in Experiment 2. The results from both experiments demonstrated a left hemisphere advantage for processing puns triggered by non-decomposable idioms; puns motivated by decomposable idioms were processed equally fast in both hemispheres, suggesting that this type of pun induced right hemisphere involvement and led to bilateral processing. We discuss the results in light of predictions derived from the ‘graded salience’ hypothesis and the ‘fine-coarse coding’ hypothesis and argue that the data are more consistent with the graded salience hypothesis.

Left-Hemisphere Delay of EEG Potentials Evoked by Standard Letter Stimuli During Rapid Serial Visual Presentation: Indicating Right-Hemisphere Advantage or Left-Hemisphere Load?

During rapid serial visual presentation (RSVP), two streams of letters simultaneously presented in the left and right visual fields (LVF and RVF) evoke visual potentials (VEPs) of EEG a few milliseconds earlier at the right (RH) than the left hemisphere (LH). This small LH VEP lag might be attributed to a RH advantage in initial processing of rapidly changing stimuli or to larger load of the LH by its specialized processing of letters from both visual fields simultaneously. In the present study, the two-stream condition was compared in two experiments to conditions with smaller instantaneous verbal load, namely with stimuli presented either solely or slightly earlier in the LVF or RVF. The RH advantage hypothesis predicts a LH VEP lag very similar to the standard two-stream condition when comparing between LH and RH VEPs contralateral to the single or earlier stream. The LH load hypothesis predicts shorter VEP latencies at the LH in the one-stream and earlier-stream than in the two-stream condition, resulting in an absent LH lag in those conditions. Results tended to be more in line with these latter predictions suggesting that in RSVP the LH might be more involved in partial processing of letters in search for target features. However, since the RH advantage hypothesis could not be reliably rejected these results might indicate a complex interplay between both hemispheres. This interplay would exploit the abilities of either hemisphere during the demanding processing of rapidly presented letters, both the LH advantage in letter processing and the RH advantage in visual perception at initial stages.

A Posterior-Anterior Distinction between Scene Perception and Scene Construction in Human Medial Parietal Cortex.

Human retrosplenial complex (RSC), located in medial parietal cortex, has been implicated in numerous cognitive functions, including scene perception, spatial navigation, and autobiographical memory retrieval. Recently, a posterior-anterior distinction within RSC was proposed, such that posterior aspects process scene-related visual information (constituting a medial place area [MPA]), whereas anterior aspects process information that is vividly retrieved from memory, thereby supporting remembering and potentially navigation. Here, we tested this proposed distinction in a single group of participants (both male and female) using fMRI with both perceptual and mnemonic tasks. After completing a resting-state scan, participants performed a task that required constructing scenes from memory and completed a scene selectivity localizer task. We tested directly perceptual and mnemonic responses in MPA and an anterior, connectivity-defined region (CON), which showed strong functional connectivity with anterior parahippocampal place area. A double dissociation was observed, such that CON was more strongly activated during scene construction than was MPA, whereas MPA was more perceptually responsive than CON. Further, peak responses from the scene construction task were anterior to perceptual peaks in all but 1 participant and hemisphere. Finally, through analyses of the posterior-anterior response profiles, we identify the fundus of the parieto-occipital sulcus as a potential location for the crossover from perceptual to mnemonic representations and highlight a potential left-hemisphere advantage for mnemonic representations. Collectively, our results support a distinction between posterior and anterior aspects of the RSC, suggesting that more specific functional-anatomic terms should be used in its place in future work.SIGNIFICANCE STATEMENT The retrosplenial complex (RSC) has been implicated in vision, spatial cognition, and memory. We previously speculated on a potential posterior-anterior distinction within RSC for scene perception and memory-based scene construction/navigation. Here, we tested this distinction through a combination of resting-state, perceptual, and mnemonic task data. Consistent with our predictions, we demonstrate that perceptual responses peak consistently posterior of those elicited by memory-based scene construction within the broader RSC. Further, we highlight (1) the fundus of the parieto-occipital sulcus as a landmark for the transition between these representations, (2) the anterior bank of parieto-occipital sulcus as the point of maximal separation between these representations, and (3) identify a potential hemispheric asymmetry in mnemonic representations. These data support functional dissociations within RSC.

What's left for balanced bilinguals? Language proficiency and item familiarity affect left-hemisphere specialization in metaphor processing.

To characterize the hemispheric processing of metaphors in bilinguals compared with monolinguals and to determine the role of language proficiency in hemispheric lateralization. Fifty-seven English-dominant Spanish-English bilinguals and 57 English speaking monolinguals participated in a divided visual field study. The two groups performed a semantic judgment task with metaphorical, literal, and unrelated word pairs presented either to the right visual field/left hemisphere or to the left visual field/right hemisphere. Bilinguals processed metaphors more slowly and less accurately than monolinguals in both visual field presentations but there was no difference between the groups in the symmetry of processing-both groups showed a left hemisphere advantage. In bilinguals, the efficiency of processing within the left, but not the right, hemisphere was predicted by language dominance scores (i.e., English minus Spanish picture naming scores). Additionally, in all participants, the left hemisphere was more sensitive than the right hemisphere to metaphor familiarity; the latter in turn was sensitive to metaphor familiarity only in balanced bilinguals (not in unbalanced bilinguals and monolinguals). These results suggest that even though bilinguals are less efficient, they rely on the same underlying cognitive mechanisms as monolinguals in linguistic processing of metaphors. Moreover, whereas the right hemisphere is coarsely affected by language proficiency, the left hemisphere, and metaphor processing therein, is more sensitive to small variations in linguistic experience. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Neurite architecture of the planum temporale predicts neurophysiological processing of auditory speech.

The left hemispheric advantage in speech perception is reflected in faster neurophysiological processing. On the basis of postmortem data, it has been suggested that asymmetries in the organization of the intrinsic microcircuitry of the posterior temporal lobe may produce this leftward timing advantage. However, whether this hypothetical structure-function relationship exists in vivo has never been empirically validated. To test this assumption, we used in vivo neurite orientation dispersion and density imaging to quantify microcircuitry in terms of axon and dendrite complexity of the left and right planum temporale in 98 individuals. We found that a higher density of dendrites and axons in the temporal speech area is associated with faster neurophysiological processing of auditory speech, as reflected by electroencephalography. Our results imply that a higher density and higher number of synaptic contacts in the left posterior temporal lobe increase temporal precision and decrease latency of neurophysiological processes in this brain region.

Early asymmetric inter-hemispheric transfer in the auditory network: insights from infants with corpus callosum agenesis.

The left hemisphere specialization for language is a well-established asymmetry in the human brain. Structural and functional asymmetries are observed as early as the prenatal period suggesting genetically determined differences between both hemispheres. The corpus callosum is a large tract connecting mostly homologous areas; some have proposed that it might participate in an enhancement of the left-hemispheric advantage to process speech. To investigate its role in early development, we compared 13 3-4-month-old infants with an agenesis of the corpus callosum ("AgCC") with 18 typical infants using high-density electroencephalography in an auditory task. We recorded event-related potentials for speech stimuli (syllables and babbling noise), presented binaurally (same syllable in both ears), monaurally (babbling noise in one ear) and dichotically (syllable in one ear and babbling noise in the other ear). In response to these stimuli, both groups developed an anterior positivity synchronous with a posterior negativity, yet the topography significantly differed between groups likely due to the atypical gyration of the medial surface in AgCC. In particular, the anterior positivity was lateral in AgCC infants while it covered the midline in typical infants. We then measured the latencies of the main auditory response (P2 at this age) for the different conditions on the symmetrical left and right clusters. The main difference between groups was a ~ 60ms delay in typical infants relative to AgCC, for the ipsilateral response (i.e. left hemisphere) to babbling noise presented in the left ear, whereas no difference was observed in the case of right-ear stimulation. We suggest that our results highlight an asymmetrical callosal connectivity favoring the right-to-left hemisphere direction in typical infants. This asymmetry, similar to recent descriptions in adults, might contribute to an enhancement of left lateralization for language processing beyond the initial cortical left-hemisphere advantage.