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Updated: May 5, 2026
Infant Auditory Processing and Event-related Brain Oscillations
Published on: July 1, 2015
Effect of interstimulus interval and age on cortical auditory evoked potentials in 10-22-week-old infants
Mridula Sharma1, Patrice K H Johnson, Suzanne C Purdy
1aAudiology Section, Macquarie University, Australia bHearing Co-operative Research Centre, Australia cThe Hearing and Balance Centre, St Vincent Hospital, Darlinghurst, New South Wales, Australia dNational Hearing Care, Australia eDepartment of Discipline of Speech Science, The University of Auckland, Auckland, New Zealand.
Insights
Cortical auditory evoked potentials (CAEPs) in infants show different responses to stimulus rates than adults. N450, an adult-like wave, only appeared in older infants, indicating maturational differences in auditory processing.
Area of Science:
- Auditory Neuroscience
- Developmental Psychology
- Pediatric Audiology
Background:
- Infant auditory evoked potentials (CAEPs) are crucial for assessing hearing and auditory development.
- Understanding the impact of stimulus rate, specifically interstimulus interval (ISI), on CAEPs is vital for accurate interpretation.
- Existing research on ISI effects is primarily based on adult and older child populations.
Purpose of the Study:
- To investigate the effect of different interstimulus intervals (ISIs) on the morphology of cortical auditory evoked potentials (CAEPs) in infants.
- To determine if longer ISIs elicit more adult-like CAEP waveforms, including the N450 component, in infants.
- To examine maturational differences in auditory processing by comparing CAEPs in younger versus older infants.
Main Methods:
- Cortical auditory evoked potentials (CAEPs) were recorded in 10 typically developing infants (4 aged 10-13 weeks, 6 aged 20-22 weeks).
- Stimuli (/da/ at 55 dB SPL) were presented at varying ISIs (910, 1820, 3640, 4550 ms) in quiet and in noise.
- Wave morphology, particularly the presence and characteristics of P1 and N450 peaks, was analyzed across different ISIs and age groups.
Main Results:
- The P1 peak was consistently observed in all infants across all ISIs.
- The N450 component, indicative of more mature auditory processing, was only present in the older infant group (20-22 weeks).
- No significant effect of ISI was found for either the younger or older infant groups, contrary to findings in adults and older children.
Conclusions:
- The absence of a clear ISI effect in very young infants suggests distinct developmental trajectories in auditory processing compared to older individuals.
- The emergence of N450 in older infants highlights maturational changes in speech-sound processing within the first few months of life.
- These findings underscore the need for age-specific interpretations of CAEPs, especially when evaluating hearing aid efficacy in infants.
Abstract:
This study compares cortical auditory evoked potentials (CAEPs) at different interstimulus intervals (ISIs) in infants to determine the impact of stimulus rate on wave morphology. Infant CAEPs are dominated by a positive peak P1. We hypothesized that infant CAEPs would be more adult-like at longer ISI with P1, followed by negativity (labelled N450). Participants were 10 typically developing infants aged 10-13 weeks (N=4) and 20-22 weeks (N=6). CAEPs were measured in one recording session for /da/ in quiet at 55 dB SPL for ISIs of 910, 1820, 3640 and 4550 ms in a randomized order. Recordings were complete at each ISI for 7-10 infants. Seven infants who completed all testing in quiet were also tested in continuous white noise (+5 dB signal-to-noise ratio) for the shortest ISI. P1 was observable in all infants; N450 was only present in the older infants. There appeared to be no ISI effect for younger or older infants, which is not consistent with ISI findings for adults and older children. The presence of N450 in the older infants only suggests that cortical maturational differences are evident in speech-evoked CAEPs in young infants. There were minimal effects of noise on P1 latency and amplitude. Results suggest different effects of ISI for very young infants than those observed in older infants and children. CAEPs are being used to measure hearing aid effectiveness in young infants and hence it is imperative that the effects of factors such as ISI are better understood.
