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Elicitation of the acoustic change complex (ACC) to long-duration speech stimuli in four-month-old infants Chen, Ke Heng


The acoustic change complex (ACC) is a cortical auditory-evoked potential (CAEP) that comprises overlapping slow cortical responses (P1-N1-P2) and occurs in response to changes during an ongoing stimulus (Martin, Tremblay, & Korczak, 2008). Research findings suggest that the ACC indicates discrimination at the level of the auditory cortex and provides insight into the brain’s capacity to process acoustic features of speech (Kaukoranta, et al., 1987; Ostroff, et al., 1998). Only one study to date has attempted to record ACCs to speech stimuli in young infants (Small & Werker, 2012). Small and Werker (2012) tested a group of English-learning four-month-old infants with speech contrasts generated from a synthetic place-of-articulation continuum: a native dental-dental contrast /dada/, dental-labial contrast /daba/, and a non-native Hindi dentalretroflex contrast /daDa/. Slow cortical responses resembling adult P1-N1-P2 complex were recorded for all conditions with significantly prolonged latencies compared with adults. Robust ACCs were elicited in most infants to /daba/ with distinct P1, N1 and P2 components, but fewer infants had ACC components in response to /dada/ and /daDa/. The author suggested that the absence of ACCs in /dada/ and /daDa/ conditions might be due to short stimulus length. The purpose of the present study was to investigate the effect of long-duration speech stimuli for eliciting ACCs in four-month-old infants. By increasing the stimulus length from 564 to 816 ms, ACCs were reliably elicited for all stimulus conditions (/dada/, /daba/ and /daDa/) in infants with more distinct cortical components and better morphology compared with previous findings (Small & Werker, 2012). The amplitude of P1 elicited to the acoustic change in /daba/ and /daDa/ was significantly larger compared iii with that of P1 for /dada/, indicating that the brain discriminated between the speech tokens. In conclusion, our results support the findings by Small and Werker (2012) showing that adult-like slow cortical responses can be recorded in young infants. Our results also suggest that ACCs can be reliably elicited in four-month-old infants given optimized stimulus parameters (e.g. longer ISIs and stimulus duration) and provide further evidence for the use of ACCs as an index of discrimination ability.

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