Posted by: Indonesian Children | August 4, 2009

Neural representation of voice onset time in infants and children



Background and Aims: The ability to encode temporal speech features such as voice onset time (VOT) is important for understanding spoken language. In adults with normal hearing, the neural representation of VOT has been primarily shown through recording morphological changes in the N1 component of the cortical auditory evoked potential (CAEP). In young children the neural representation of temporal speech features is largely unknown, however. One difficulty in studying neural representation of VOT in infants and children is that the N1 component is not reliably present until age nine. In infancy and early childhood the CAEP is dominated by a single positive peak, known as P1, while N1 does not emerge until late childhood. Thus, we sought to examine whether the neural representation of VOT could be recorded through measuring changes in the P1 component of the CAEP of young children.

Methods: Cortical auditory evoked potentials were recorded in 18 normally hearing children, aged 2-7 years. Neuroscan STIM and SCAN (version 4.3) evoked potential system was used for stimulus generation and CAEP recording. A silver-chloride electrode was placed over the midline (Cz). A reference electrode was placed on the nose, with a ground electrode placed on the forehead. The stimulus continuum consisted of four tokens in which VOT values varied in 20 ms steps from 0 – 60 ms. The tokens were identical to those used by Sinex et al. (1991) and Sharma et al. (1999; 2000). Stimuli were presented via a loudspeaker at 75 dB SPL at a distance of 1 meter.

Key Results: P1 amplitude and latency was identified for all subjects. The amplitude of P1 was defined as the largest positive deflection occurring between 75 – 150 ms after stimulus onset. The latency of the peak was measured at the centre of the peak. A one way ANOVA to determine the effects of stimulus type on the latencies and amplitudes of P1 showed significant differences in the latency of P1, related to the encoding of VOT. The stimuli with the shorter VOT values of 0 and 20 ms (/da/) elicited significantly earlier P1 latencies than the stimuli with longer VOT values of 40 and 60 ms (/ta/).

Conclusions: All infants and children showed a distinct neural response pattern, as reflected by a P1 latency shift to speech stimuli with VOT values greater than 40 ms. An understanding of the representation of VOT at the neural level is important because it may provide a method for studying temporal processing of speech features in children with impaired auditory pathways. The procedure may also be a useful tool for assessing the influence of various types of auditory habilitation and evaluating clinical populations that are unable to cooperate for behavioral testing.

Paper presented at the annual meeting of the XVth Biennial International Conference on Infant Studies, Westin Miyako, Kyoto, Japan, Jun 19, 2006

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