The maturation of the acoustic change complex in response to iterated ripple noise in normal-hearing toddlers

With the introduction of newborn hearing screening and early intervention programs, there has been an increase in the number of early-identified hearing loss. However, clinical audiological test batteries do not currently include an objective (i.e., not requiring responses from the patient) measure of speech discrimination in very young infants and difficult-to-test populations. The ability to process temporal speech cues to discriminate between speech sounds is disrupted in all degrees of sensorineural hearing loss and in populations with auditory neuropathy spectrum disorder. The purpose of this study was to investigate the maturational time course of a cortical auditory evoked potential, the acoustic change complex (ACC) elicited to iterated ripple noise (IRN), as a possible clinical measure of speech perception capacity. Previously, Small et al. (in prep) determined that ACC responses to IRN stimuli are not mature in infants up to 16 months old. Participants were 27 children divided into two groups: 13 younger children (22 to 32 months; 6 males) and 14 older children (38 to 59 months; 5 males). IRN stimuli were created with varying degrees of pitch saliency by adjusting the number of iterations (4, 8, 16 & 32); each 500-ms IRN stimulus was concatenated to a 500-ms noise stimulus to generate noise-IRN (experimental) and noise-noise (control) conditions. Onset and ACC responses were recorded to all conditions presented binaurally under insert earphones while children were awake. All children had responses present to every IRN condition for at least one electrode site. Latencies decreased significantly as the number of iterations increased and the older children had significantly shorter ACC latencies than the younger group. Amplitudes were significantly smaller for the younger children compared to the older children; however, the effect of condition on ACC amplitudes between age groups did not reach significance. Children as young as 22 months old have ACC responses elicited to low-saliency pitch stimuli, indicating that IRN discrimination abilities are emerging in this age group. Future research will determine how these processing abilities correlate with functional speech abilities in children with normal hearing and hearing loss.Medicine, Faculty ofAudiology and Speech Sciences, School ofGraduat