Identification of asynchronous monaural and dichotic vowel pairs across the adult lifespan

Temporal onset asynchrony is one cue that listeners use to identify concurrent vowels. Young (N=80; 18-31 years), middle-age (N=40; 40-55 years), and older (N=150; 60-88 years) adults identified vowel pairs in a temporal-order paradigm under monaural and dichotic stimulus presentations. Experiments used forced-choice constant-stimuli methods to determine the smallest stimulus onset asynchrony (SOA) between brief 70-ms vowels that enabled identification of the stimulus sequence. Vowels modified from four words (pit, pet, pot, and put) served as stimuli. All listeners identified the vowels in isolation with better than 90% accuracy. Results indicated that older listeners performed significantly poorer on monaural and dichotic temporal-order identification tasks than young listeners, with middle-age listeners in between. Correlations of performance with age across the full age span were moderate. For all three groups, SOAs for the dichotic task were significantly longer than those for the monaural task. A significant main effect of vowel pair was observed, indicating that not all vowel pairs were equally identifiable. Patterns of vowel pair identification were similar across all groups for both monaural and dichotic presentations; however, interactions with age group were observed. Effects of vowel order and dominance were also observed.