Abstract
In deaf children, huge emphasis was given to language; however, emotional cues decoding and production appear of pivotal importance for communication capabilities. Concerning neurophysiological correlates of emotional processing, the gamma band activity appears a useful tool adopted for emotion classification and related to the conscious elaboration of emotions. Starting from these considerations, the following items have been investigated: (i) whether emotional auditory stimuli processing differs between normal-hearing (NH) children and children using a cochlear implant (CI), given the non-physiological development of the auditory system in the latter group; (ii) whether the age at CI surgery influences emotion recognition capabilities; and (iii) in light of the right hemisphere hypothesis for emotional processing, whether the CI side influences the processing of emotional cues in unilateral CI (UCI) children. To answer these matters, 9 UCI (9.47 ± 2.33 years old) and 10 NH (10.95 ± 2.11 years old) children were asked to recognize nonverbal vocalizations belonging to three emotional states: positive (achievement, amusement, contentment, relief), negative (anger, disgust, fear, sadness), and neutral (neutral, surprise). Results showed better performances in NH than UCI children in emotional states recognition. The UCI group showed increased gamma activity lateralization index (LI) (relative higher right hemisphere activity) in comparison to the NH group in response to emotional auditory cues. Moreover, LI gamma values were negatively correlated with the percentage of correct responses in emotion recognition. Such observations could be explained by a deficit in UCI children in engaging the left hemisphere for more demanding emotional task, or alternatively by a higher conscious elaboration in UCI than NH children. Additionally, for the UCI group, there was no difference between the CI side and the contralateral side in gamma activity, but a higher gamma activity in the right in comparison to the left hemisphere was found. Therefore, the CI side did not appear to influence the physiologic hemispheric lateralization of emotional processing. Finally, a negative correlation was shown between the age at the CI surgery and the percentage of correct responses in emotion recognition and then suggesting the occurrence of a sensitive period for CI surgery for best emotion recognition skills development.
Highlights
Processing emotional expressions is fundamental for social interactions and communication; from a very young age, infants are able to detect visual and auditory information in faces and voices of people around them (Grossmann, 2010)
This statement is supported by the results of studies employing the McGurk effect on cochlear implant (CI) users, which requires the integration of auditory and visual sensory stimuli
The task consisted of the recognition of nonverbal vocalizations belonging to a database previously validated and employed in several studies (Sauter et al, 2006, 2010, 2013) and grouped into three emotional states: positive, negative, and neutral, which participants were asked to match with the corresponding emotional picture (Figure 1)
Summary
Processing emotional expressions is fundamental for social interactions and communication; from a very young age, infants are able to detect visual and auditory information in faces and voices of people around them (Grossmann, 2010) Such capability would develop into the skill to recognize and discriminate emotions, thanks to the contribution of the experience and of the maturation of sensory and perceptual systems. In post-lingually deaf CI patients, such greater relying on visual information, indexed by higher speech-reading performances than normal-hearing (NH) individuals, led instead to an increased capacity of integrating visual and distorted speech signals, producing higher visuoauditory performances (Rouger et al, 2007) Such evidence in postlingual deaf patients was supported by neurophysiological assessments, evidencing a positive correlation between visual activity and auditory speech recovery, suggesting a facilitating role for the visual modality in auditory words’ perception during communicative situations (Strelnikov et al, 2013). Such results strongly support the hypothesis of a sensitive period (Kral et al, 2001; Sharma et al, 2005; Gilley et al, 2010) for the establishment of the integration of auditory and visual stimuli
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