Date of Degree

9-2021

Document Type

Dissertation

Degree Name

Ph.D.

Program

Speech-Language-Hearing Sciences

Advisor

Brett A. Martin

Committee Members

Michelle Macroy-Higgins

John Preece

Miwako Hisagi

Subject Categories

Speech and Hearing Science

Keywords

Acoustic Change Complex (ACC), Speech, Maturation, Efficiency, Auditory Evoked Potentials (AEPs)

Abstract

The acoustic-change-complex (ACC) is an objective measure that can be used to study whether sounds are encoded at the level of the cortex. The goals of this study were: 1) To determine if the ACC can be elicited in infants, and 2) To establish whether eliminating the silent interval between stimuli and using a continuously alternating stimulus is more efficient in infants than the traditional interrupted stimulus presentation method. If the continuously alternating stimulus is more efficient, then 3) To determine why the continuously alternating stimulus is more efficient.

Twenty-one infants aged 2 months to 13 months old served as participants. A 70 dB SPL synthetic vowel containing 1000 Hz changes of second formant frequency, perceived as a change between the point vowels /u/ and /i/, was used to elicit the ACC. The ACC was recorded in four stimulus presentation strategies: 1) interrupted presentation of a 1 second stimulus that contained a single change from /u/ to /i/ using a 2 second inter-onset interval; 2) interrupted presentation of the same stimulus using a 1 second inter-onset interval; 3) interrupted presentation of a 1.5 second /uiu/ stimulus using a 2 second inter-onset interval; and 4) presentation of a stimulus that continuously alternated between /u/ and /i/ using a 1 second repetition interval. The evoked potentials were recorded from surface electrodes using a Neuroscan system.

The results demonstrated that the ACC can be elicited in infants 2 to 13 months of age and that the continuously alternating stimulus presentation was the most efficient method to elicit the ACC. Reducing the inter-onset interval from 2 to 1 second increased efficiency by a factor of 2.15. The inclusion of two directions of change increased efficiency by a factor of 1.46. Combining both, increased efficiency by a factor of 2.54.

In conclusion, the ACC was elicited in infants between 2 and 13 months of age. Highest efficiency was obtained for the continuous alternating stimulus presentation strategy. Therefore, eliminating silent intervals between stimuli and doubling the number of acoustic changes presented produced an ACC in a more efficient manner. This provides more information on the encoding of speech in infants and has implications for clinical application of the ACC.

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