Functional selectivity for face processing in the temporal voice area of early deaf individuals.

Brain systems supporting face and voice processing both contribute to the extraction of important information for social interaction (e.g., person identity). How does the brain reorganize when one of these channels is absent? Here, we explore this question by combining behavioral and multimodal neuroimaging measures (magneto-encephalography and functional imaging) in a group of early deaf humans. We show enhanced selective neural response for faces and for individual face coding in a specific region of the auditory cortex that is typically specialized for voice perception in hearing individuals. In this region, selectivity to face signals emerges early in the visual processing hierarchy, shortly after typical face-selective responses in the ventral visual pathway. Functional and effective connectivity analyses suggest reorganization in long-range connections from early visual areas to the face-selective temporal area in individuals with early and profound deafness. Altogether, these observations demonstrate that regions that typically specialize for voice processing in the hearing brain preferentially reorganize for face processing in born-deaf people. Our results support the idea that cross-modal plasticity in the case of early sensory deprivation relates to the original functional specialization of the reorganized brain regions.

Environmental Learning of Social Cues: Evidence From Enhanced Gaze Cueing in Deaf Children.

The susceptibility to gaze cueing in deaf children aged 7-14 years old (N = 16) was tested using a nonlinguistic task. Participants performed a peripheral shape-discrimination task, whereas uninformative central gaze cues validly or invalidly cued the location of the target. To assess the role of sign language experience and bilingualism in deaf participants, three groups of age-matched hearing children were recruited: bimodal bilinguals (vocal and sign-language, N = 19), unimodal bilinguals (two vocal languages, N = 17), and monolinguals (N = 14). Although all groups showed a gaze-cueing effect and were faster to respond to validly than invalidly cued targets, this effect was twice as large in deaf participants. This result shows that atypical sensory experience can tune the saliency of a fundamental social cue.

Multisensory Interference in Early Deaf Adults.

Multisensory interactions in deaf cognition are largely unexplored. Unisensory studies suggest that behavioral/neural changes may be more prominent for visual compared to tactile processing in early deaf adults. Here we test whether such an asymmetry results in increased saliency of vision over touch during visuo-tactile interactions. About 23 early deaf and 25 hearing adults performed two consecutive visuo-tactile spatial interference tasks. Participants responded either to the elevation of the tactile target while ignoring a concurrent visual distractor at central or peripheral locations (respond to touch/ignore vision), or they performed the opposite task (respond to vision/ignore touch). Multisensory spatial interference emerged in both tasks for both groups. Crucially, deaf participants showed increased interference compared to hearing adults when they attempted to respond to tactile targets and ignore visual distractors, with enhanced difficulties with ipsilateral visual distractors. Analyses on task-order revealed that in deaf adults, interference of visual distractors on tactile targets was much stronger when this task followed the task in which vision was behaviorally relevant (respond to vision/ignore touch). These novel results suggest that behavioral/neural changes related to early deafness determine enhanced visual dominance during visuo-tactile multisensory conflict.

Finding the balance between capture and control: Oculomotor selection in early deaf adults.

Previous work investigating the consequence of bilateral deafness on attentional selection suggests that experience-dependent changes in this population may result in increased automatic processing of stimulus-driven visual information (e.g., saliency). However, adaptive behavior also requires observers to prioritize goal-driven information relevant to the task at hand. In order to investigate whether auditory deprivation alters the balance between these two components of attentional selection, we assessed the time-course of overt visual selection in deaf adults. Twenty early-deaf adults and twenty hearing controls performed an oculomotor additional singleton paradigm. Participants made a speeded eye-movement to a unique orientation target, embedded among homogenous non-targets and one additional unique orientation distractor that was more, equally or less salient than the target. Saliency was manipulated through color. For deaf participants proficiency in sign language was assessed. Overall, results showed that fast initiated saccades were saliency-driven, whereas later initiated saccades were goal-driven. However, deaf participants were overall slower than hearing controls at initiating saccades and also less captured by task-irrelevant salient distractors. The delayed oculomotor behavior of deaf adults was not explained by any of the linguistic measures acquired. Importantly, a multinomial model applied to the data revealed a comparable evolution over time of the underlying saliency- and goal-driven processes between the two groups, confirming the crucial role of saccadic latencies in determining the outcome of visual selection performance. The present findings indicate that prioritization of saliency-driven information is not an unavoidable phenomenon in deafness. Possible neural correlates of the documented behavioral effect are also discussed.

Linguistic and pragmatic skills in toddlers with cochlear implant.

BACKGROUND: An increasing number of deaf children received cochlear implants (CI) in the first years of life, but no study has focused on linguistic and pragmatic skills in children with CI younger than 3 years of age. AIMS: To estimate the percentage of children who had received a CI before 2 years of age whose linguistic skills were within the normal range; to compare linguistic skills of children implanted by 12 months of age with children implanted between 13 and 26 months of age; and to describe the relationship among lexical, grammar and pragmatic skills. METHODS & PROCEDURES: The participants consisted of children who were included on the patient lists of the Service of Audio-Vestibology of the Circolo Hospital in Varese, Italy, and met the following criteria: chronological age between 18 and 36 months; CI activated between 8 and 30 months of age; absence of other reported deficits; hearing parents; and not less than 6 months of CI experience. Language development was evaluated through MacArthur-Bates CDI; pragmatic skills (assertiveness and responsiveness) were evaluated through the Social Conversational Skills Rating Scale. The scores obtained were transformed into z-scores and compared with normative data. The relationship among lexical, grammar and pragmatic skills were tested using Spearman Rho correlations. Children with CI were divided into groups based on the age at CI activation and the differences between the two groups were tested using the Student's t-test. OUTCOMES & RESULTS: Data from 23 deaf children were collected. Fewer than half of the children were within the normal range for lexical production and use of sentences; more than one-third of them fell below the normal range for both lexical and grammar skills. No significant difference was found in vocabulary size or early grammar skills when comparing children who received the CI by 12 months of age with those implanted during the second year of life. Despite the strong relationship among lexical, grammar and pragmatic skills, the delays found for grammar and pragmatic skills were greater than expected based on the vocabulary size. Age at diagnosis of hearing loss was the only predictor of vocabulary size. CONCLUSIONS & IMPLICATIONS: CI may provide deaf children with a good opportunity to develop language skills, but severe difficulties in early social experiences and interaction mediated by language still remain. Delays in these aspects suggest that interventions improving pragmatic skills are recommended even on very young children with CI.

Increased overt attention to objects in early deaf adults: An eye-tracking study of complex naturalistic scenes.

The study of selective attention in people with profound deafness has repeatedly documented enhanced attention to the peripheral regions of the visual field compared to hearing controls. This finding emerged from covert attention studies (i.e., without eye-movements) involving extremely simplified visual scenes and comprising few visual items. In this study, we aimed to test whether this key finding extends also to overt attention, using a more ecologically valid experimental context in which complex naturalistic images were presented for 3 s. In Experiment 1 (N = 35), all images contained a single central object superimposed on a congruent naturalistic background (e.g., a tiger in the woods). At the end of the visual exploration phase, an incidental memory task probed the participants' recollection of the seen central objects and image backgrounds. Results showed that hearing controls explored and remembered the image backgrounds more than deaf participants, who lingered on the central object to a greater extent. In Experiment 2 we aimed to disentangle if this behaviour of deaf participants reflected a bias in overt space-based attention towards the centre of the image, or instead, enhanced object-centred attention. We tested new participants (N = 42) in the visual exploration task adding images with lateralized objects, as well as images with multiple object or images without any object. Results confirmed increased exploration of objects in deaf participants. Taken together our novel findings show limitations of the well-known peripheral attention bias of deaf people and suggest that visual object-centred attention may also change after prolonged auditory deprivation.

Spatial and non-spatial multisensory cueing in unilateral cochlear implant users.

In the present study we examined the integrity of spatial and non-spatial multisensory cueing (MSC) mechanisms in unilateral CI users. We tested 17 unilateral CI users and 17 age-matched normal hearing (NH) controls in an elevation-discrimination task for visual targets delivered at peripheral locations. Visual targets were presented alone (visual-only condition) or together with abrupt sounds that matched or did not match the location of the visual targets (audio-visual conditions). All participants were also tested in simple pointing to free-field sounds task, to obtain a basic measure of their spatial hearing ability in the naturalistic environment in which the experiment was conducted. Hearing controls were tested both in binaural and monaural conditions. NH controls showed spatial MSC benefits (i.e., faster discrimination for visual targets that matched sound cues) both in the binaural and in the monaural hearing conditions. In addition, they showed non-spatial MSC benefits (i.e., faster discrimination responses in audio-visual conditions compared to visual-only conditions, regardless of sound cue location) in the monaural condition. Monaural CI users showed no spatial MSC benefits, but retained non-spatial MSC benefits comparable to that observed in NH controls tested monaurally. The absence of spatial MSC in CI users likely reflects the poor spatial hearing ability measured in these participants. These findings reveal the importance of studying the impact of CI re-afferentation beyond auditory processing alone, addressing in particular the fundamental mechanisms that serves orienting of multisensory attention in the environment.

Attentional orienting to social and nonsocial cues in early deaf adults.

In 2 experiments we investigated attentional orienting to nonpredictive social and nonsocial cues in deaf observers. In Experiment 1a, 22 early deaf adults and 23 hearing controls performed a peripheral shape-discrimination task, while uninformative central gaze cues validly and invalidly cued the location of the target. As an adaptation to the lack of audition, we expected deaf adults to show a larger impact of gaze cuing on attentional orienting compared with hearing controls. However, contrary to our predictions, deaf participants did not respond faster to cued compared with uncued targets (gaze-cuing effect; GCE), and this behavior partly correlated with early sign language acquisition. Experiment 1b showed a reliable GCE in 13 hearing native signers, thus excluding a key role of early sign language acquisition in explaining the lack of GCE in the response times of deaf participants. To test whether the resistance to uninformative central cues extends to nonsocial cues, in Experiment 2 nonpredictive arrow cues were presented to 14 deaf and 14 hearing participants. Both groups of participants showed a comparable arrow-cuing effect. Together, our findings suggest that deafness may selectively limit attentional-orienting triggered by central irrelevant gaze cues. Possible implications for plasticity related to deafness are discussed.