Exponential modeling of frequency-following responses in American neonates and adults

Abstract

Frequency-following response (FFR) has been widely used to assess the mechanisms of speech processing for speakers of tonal and non-tonal languages. For Chinese speaking adults, the characteristics of speech processing with increasing number of sweeps have been described with an exponential curve-fitting model; however, these characteristics for non-tonal language speakers have yet to be described in a similar manner. This study examined the characteristics of speech processing for both adults and neonates who speak a non-tonal language, to determine the goodness-of-fit of an exponential model to neonatal and adult FFRs, and compared the results between groups to determine if any differences exist. Twelve American neonates and 12 American adults were recruited for this study. Participants were native English speakers. The FFR was elicited using the English vowel /i/ with a rising pitch contour for a total of 8000 sweeps from each participant. From the three indices (Frequency Error, Tracking Accuracy and Pitch Strength) computed, the FFR trends were fit to an exponential curve-fitting model to estimate the frequency tracking acuity and neural phase-locking magnitude when the amount of sweeps increased in the averaged waveform. Significant differences between groups were found for the objective indices.