The behavioral and neurophysiologic correlates of vowel processing in Italian cochlear-implant and normal-hearing children.
Unilateral cochlear implants (henceforth, CI) partially restore auditory sensation in children affected by congenital, bilateral, and severe to profound neurosensorial hearing loss, especially if the CI surgery takes place during the sensitive period for central auditory pathway maturation (until 44months) [Bishof 2007]. For the first time, this study investigates detection, identification, and discrimination of /i, u, e, o, a/ in a group of congenitally-deaf, early-implanted, Italian children (mean age at CI surgery: 33 months, mean age at testing: 109 months), wearing their CI on their right ear, and in a group of age-matched controls (henceforth NH children) living in the province of Lecce (Apulia, Southern Italy). Vowel detection, identification, and discrimination will be investigated by combining behavioral measures (active vowel identification and discrimination tasks) and neurophysiologic measures (passive EEG recording and extraction of the P1, N1, MMN, and P3a responses evoked by vowel presentation) [Korkzac et al. 2005; Purdy et al. 2005; Martin et al. 2008]. The aim of this study is twofold. First, we want to ascertain whether or not Italian CI children detect, identify, and discriminate vowels building on a time window and an accuracy comparable to those exhibited by NH children, both at the behavioral and at the neurophysiologic levels. Second, we aim at determining whether, and to what extent, age at surgery (mean: 33months, range: 23-54months) and length of CI use (mean: 76months, range: 28-97months) affect vowel processing in early-implanted Italian children. Building on the results achieved by previous ERP studies on CI children exposed to English, French, Dutch, and Finnish [Sharma et al. 2005, 2007, 2009; Beynon et al. 2002; Singh et al. 2004; Henkin et al. 2008], we expect Italian CI children to need a prolonged time window and/or to rely on a lower accuracy in vowel processing with respect to NH children, both at the behavioral and at the neurophysiologic levels. We also expect those Italian deaf children who received their CI earlier and/or who benefit from a longer CI use to process vowels more quickly and more accurately compared to the other CI children. The international research group consists of Dr. Luigia Garrapa (University of Padova and University of Salento, Italy), Prof. Mirko Grimaldi (University of Salento, Italy), Dr. Davide Bottari (University of Hamburg, Germany), Prof. Francesco Pavani (University of Trento, Italy), Prof. Andrea Calabrese (University of Connecticut, USA), Dr. Michele De Benedetto (UOC of ORL, Hospital ï¿½Fazziï¿½ in Lecce), and Dr. Silvano Vitale (UOC of ORL, Hospital ï¿½Fazziï¿½ in Lecce).
Cortical vowel processing in typically-developing Italian children: an ERP study.
In typically-developing individuals, the auditory cortex is responsible for speech sound processing. Identification and discrimination of native speech sounds takes place when native vowels and consonants are recognized and their long-term memory representations, stored in the auditory cortex, are activated [Pulvermï¿½ller & Shyrov 2006; Nï¿½ï¿½tï¿½nen et al. 2011]. Speech sound processing (i.e. detection, identification, and discrimination) at the level of the auditory cortex can be easily investigated by means of the auditory Event-Related Potentials (ERPs), both in normal and pathologic, adult and pediatric subjects [Kujala et al. 2007; Martin et al. 2008; Nï¿½ï¿½tï¿½nen et al. 2011; Duncan et al. 2010]. Passively recorded ERPs are brain responses automatically elicited by auditory sounds (typically speech) and they provide information regarding the timing (through ERP latency, measured in milliseconds), accuracy (through ERP amplitude, measured in microvolts), hemisphere involvement (through scalp topography of ERP latency and amplitude), and neuronal activation (through ERP duration) in speech sound processing. For the first time, this study investigates the neurophysiological correlates of cortical processing (i.e. detection, identification, and discrimination) of 5 Italian vowels (/i, u, e, o, a/) in Southern Italian school-age children (mean age at testing: 92 months, range: 51-131 months), all right-handed. Three ERP components are of intetest in this study: the P1, N1, and MMN responses. The P1 and N1 responses indicate that vowels have been detected and identified, in turn [Sharma et al. 2005; Hyde 1997; Nï¿½ï¿½tï¿½nen et al. 2011]. The MMN response indexes that vowels have been recognized as native phonemes and phonetically discriminated with respect to their acoustic and articulatory characteristics [Nï¿½ï¿½tï¿½nen et al. 2011]. Crucially, the parameters of the N1 and MMN responses appear to be modulated by the vowel-specific acoustic features [Obleser et al. 2003; Scharinger et al. 2012]. The aim of this study is threefold. First, we will provide the exact parameters (i.e. the peak latency and amplitude as well as the component duration) of the P1, N1, and MMN responses evoked by Italian vowels in typically-developing, school-age children. The P1, N1, and MMN parameters detailed in this study may be used as a reference for future work on speech sound processing in typically-developing or patologic Italian children. Second, we will investigate scalp distribution of the P1, N1, and MMN responses over the left and the right hemispheres in order to ascertain whether or not the left hemisphere in more involved in speech sound processing in right-handed children. Third, we will determine whether, and to what extent, the N1 and MMN parameters are vowel-specific in terms of latency, amplitude, and duration as well as whether some vowels which are processed more rapidly or evoke ERP components endowed with a higher amplitude and/or a longer duration compared to other vowels. The international research group is formed by Dr. Luigia Garrapa (University of Padova and University of Salento, Italy), Prof. Mirko Grimaldi (University of Salento, Italy), Dr. Davide Bottari (University of Hamburg, Germany), Prof. Francesco Pavani (University of Trento, Italy), Prof. Andrea Calabrese (University of Connecticut, USA), Dr. Michele De Benedetto (UOC of ORL, Hospital ï¿½Fazziï¿½ in Lecce), and Dr. Silvano Vitale (UOC of ORL, Hospital ï¿½Fazziï¿½ in Lecce).