High and Front Vowel Processing in Italian Cochlear-implant Children: a Behavioral and Neurophysiologic Study

Cochlear implants (CI) partially restore auditory sensation in deaf individuals affected by an hearing impairment >70dB. Event-related potentials (ERPs) are are brain responses automatically elicited by auditory sounds. ERPs provide information regarding several dimentions of speech sound processing, such as timing (via peak latency), accuracy/strength (via peak amplitude), size of neuronal activation (via area under the curve or 'AUC'), and hemisphere involvement (via scalp topography) in native phoneme detection (through P1), identification (through N1), and discrimination (through MMN) [Martin et al. 2008]. Previous ERP studies on consonant processing by CI children found that children implanted earlier in their lives (<42 months) process consonants better in terms of accuracy/strength and processing time than late-implanted children [Beynon et al. Vowel processing, on the other hand, has been investigated only in late-implanted children, without exploring the possible influence of length of CI use [Kileny et al. 1997; Beynon et al. 2002; Henkin et al. 2008]. ERP studies comparing speech sound processing in CI and normal-hearing (NH) children found that CI children present ERP responses with smaller amplitudes and/or prolonged latencies compared to NH children. These atypical ERP response patterns suggest that CI children process speech sounds with a lower strength and/or accuracy and that they may need additional time compared to NH children [Kileny et al., 1997; Beynon et al., 2002; Gilley et al., 2008]. If there is an increasing body of literature on neurophysiologic studies on CI children exposed to English, French, Dutch, and Finnish, this is not true for Italian. Additionally-and crucially-, no previous studies have investigated speech sound processing in CI children implanted within and after the sensitive period for central auditory pathway maturation by combining neurophysiologic (automatic) and true behavioral (attentive) measures. Combining behavioral and neurophysiologic measures is of crucial importance, however, since some CI users may show poor behavioral – but good neurophysiologic – speech sound discrimination [Beynon et al., 2002], while others may present the reverse pattern [Henkin et al., 2008]. This study investigates processing of /i/, /u/, and // in 8 deaf Italian children wearing unilateral CI (age at testing = 109 months; age at surgery = 33 months; length of CI use at testing = 76 months) and in 9 age-matched NH children using both behavioral and neurophysiologic measures. while children were watching a silent movie. P1, N1, and MMN were measured on 8 fronto-central electrodes: i) P1 and N1 were identified on all stimuli …