You are invited to attend Stephanie Strahm’s Master’s thesis defense!

When: Thursday 21 November, 9:30am
Where: Room 355, Friedman Building, 2177 Wesbrook Mall
Title: “The Maturation of the Acoustic Change Complex in Response to Iterated Ripple Noise in Normal-Hearing Toddlers”
Candidate: Stephanie Strahm
Committee: Rae Riddler, Valter Ciocca, and Susan Small (Chair)


With the introduction of newborn hearing screening and early intervention programs, there has been an increase in the number of infants identified in infancy with hearing losses. However, the clinical audiological test battery currently does not include an objective measure of speech discrimination abilities to predict hearing aid outcomes 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 as well as in populations with auditory neuropathy spectrum disorder. The purpose of this study was to continue to investigate the maturational time course of a cortical auditory evoked potential, the acoustic change complex (ACC), as a possible objective clinical measure of speech perception using iterated ripple noise (IRN) to assess auditory temporal processing. Previously, Small et al. (in prep) determined that ACC responses to IRN stimuli are not mature in infants up to 16 months old.

IRN stimuli were created with varying iterations (4, 8, 16, and 32). Higher iterations of IRN stimuli correspond to greater temporal pitch saliency. Participants were 27 children ages 1 to 4 years old divided into two groups (22-32 months, mean = 27 months; n = 13, 6 males and 38-59 months, mean= 48 months; n = 14, 5 males). IRN stimuli were presented binaurally to quiet, alert children while responses were recorded through three scalp electrodes.

Both groups had ACC responses elicited to the lowest saliency IRN stimuli. Older children showed ACC responses with significantly shorter latencies than the younger group. Across conditions, latency significantly decreased with higher iterations. Older children also had significantly smaller ACC amplitudes than the younger group. Within each age group, the pattern of amplitudes increasing with increasing IRN iterations was seen.

Children as young as 22 months old have ACC responses elicited to low-saliency pitch stimuli. This indicates that auditory temporal processing abilities are emerging in this age but are not fully mature by 59 months old.