The effect of amplitude modulation on intelligibility of time-varying sinusoidal speech in children and adults.

Although researchers are currently studying auditory object formation in adults, little is known about the development of this phenomenon in children. Amplitude modulation has been suggested as one of the characteristics of the speech signal that allows auditory grouping. In this experiment, we evaluated children (4 to 13 years of age) and adults to examine whether children's ability to use amplitude modulation (AM) in perception of time-varying sinusoidal (TVS) sentences is different from that of adults, and whether there are developmental changes. We evaluated performance on recognition of TVS sentences (unmodulated, amplitude-comodulated at 25, 50, 100, and 200 Hz, and amplitude-modulated using conflicting frequencies). Overall, the youngest children performed more poorly than did older children and adults. However, difference scores, defined as the percentage of phonemes correct in a given modulation condition minus the percentage correct for the unmodulated condition, showed no significant effects of age. Unlike the findings of previous studies (Carrell & Opie, 1992), these results support the ability of modulation with conflicting frequencies to improve intelligibility. The present study provides evidence that children and adults receive the same benefits (or decrements) from amplitude modulation.