Age differences in the influence of metrical structure on phonetic identification

Two phonetic identification experiments were conducted with two groups of participants: a young adult group and an older adult group. In Experiment 1, subjects were required to make voiced-voiceless decisions for initial alveolar stop consonants to stimuli along two voice onset time (VOT) continua--one ranging from "di'gress" to "ti'gress" and the other from "'digress" to "'tigress" (i.e., in one continuum, the voiced endpoint was consistent with the word's stress pattern while in the other continuum, the voiceless endpoint was consistent with the word's stress pattern). Results revealed that both groups of participants were influenced by the stress pattern of the stimuli, but stress seemed to override VOT cues for a large number of the older individuals. To confirm that the effect was not simply due to a lexical influence, a follow-up experiment utilized two word-nonword continua ("diamond-tiamond" and "diming-timing") to examine the magnitude of lexical effects in these subject groups. Typical lexical status effects emerged for both young and older adults which were smaller than the effects of stress pattern found in Experiment 1. The findings are discussed with respect to the role of prosodic context in language processing in aging.