The development of amplitude modulation as an auditory grouping cue

The purpose of this research project was to determine whether children use amplitude modulation (AM) as a grouping cue in the formation of auditory objects. Children from 4 to 13 years of age, as well as adults, were evaluated to examine whether children\u27s ability to use AM in sentence perception is different from adults and whether this ability changes with development. Although researchers are currently studying auditory object formation in adults, little is known about the development of this phenomenon in children. Because the study of auditory grouping in speech perception is complicated by the fact that speech contains numerous redundant acoustic characteristics, time varying sinusoidal (TVS) speech was used. New stimuli were developed based on age-appropriate sentences. Performance on recognition of TVS sentences (unmodulated, amplitude comodulated at four frequencies, and amplitude modulated using conflicting frequencies) was evaluated. In general, the youngest children performed more poorly on recognition tasks than did older children and adults. However, accuracy improvements based on amplitude modulation showed no significant effects of age or language level. Difference scores, defined as percent phonemes correct in a given modulation condition minus percent correct for the unmodulated (0mod) condition, indicated that subjects performed more poorly in the 200 Hz modulation condition than they did in the unmodulated condition. While difference scores were positive for all other modulation conditions, low difference scores for the 25 Hz modulation condition compared to 50 Hz, 100 Hz, and conflicting modulation conditions would seem to preclude a CMR-like mechanism underlying performance. While previous research had suggested that amplitude comodulation was necessary for improving sentence recognition, subjects in the present study performed as well with conflicting amplitude modulation as with amplitude comodulation at 100 Hz. While the this study provides evidence that children and adults receive the same benefits (or decrements) from amplitude modulation, the underlying causes for listeners\u27 performance remain unclear. Additional research will be needed to investigate those causes. (This research was supported by NIH grants F31 D0006582 and P30 DC04662