Infants' use of onset asynchrony in the segregation of concurrent vowels

Abstract

Separating speech from competing speech is a difficult task for infants even though their ability to encode sounds appears to be mature. One possible explanation is that infants have greater difficulties extracting speech from the complex sound mixture arriving at their ears. Adults use acoustic cues such as differences in onset or harmonicity to group components that belong to the same sound source and separate those that do not. The sparse evidence on how infants segregate sounds indicates that they use some of these acoustic cues. However, temporal cues, which are strong cues for adults, have not been investigated in infants. This study examined infants’ ability to use onset asynchrony cues to separate simultaneous vowels using a single-interval observer-based procedure. Three- and seven-month-old infants and young adults were trained to identify one target vowel in a modified double-vowel paradigm. Listeners were tested in a simultaneous onset condition and either a 100 or 200 ms asynchrony condition. Cue benefit was defined as the improvement in sensitivity resulting from the addition of the asynchrony cue. Pilot data indicates that an onset asynchrony of 100ms improves performance for all age groups and that the cue benefit increases with age.