Infants’ Use of Temporal Cues in the Segregation of Concurrent Sounds

Thesis (Ph.D.)--University of Washington, 2018Infants have greater difficulties processing speech in the presence of competing sounds than adults. The mature auditory system solves this task in part by separating sounds that have different acoustic characteristics such as onset, temporal envelope or fundamental frequency. The current work evaluated whether 3- and 7-month-old infants use two different acoustic characteristics, onset asynchrony and temporal envelope, similarly to adults in the segregation of concurrent vowels. To this end, listeners were presented with superimposed vowels, consisting of 2 concurrent vowels spoken by two different-sex talkers, and were trained to respond to one specific target vowel. Three studies were conducted to evaluate infants’ use of 1) onset asynchrony, 2) envelope differences, and 3) combined onset asynchrony and envelope differences. The results indicated that 3-month-old infants were better able to segregate vowels with different onset, but not with different envelopes or a combination of onset and envelope differences. In contrast, by 7-months of age, infants used isolated and combined differences in onset and envelopes to the same extent as adults. Thus, after 7-months of age, an inability to use differences in onset and temporal envelopes cannot account for infants’ difficulties processing competing speech sounds