STIMULUS VARIABILITY AND SPOKEN WORD RECOGNITION .2. THE EFFECTS OF AGE AND HEARING IMPAIRMENT

Three experiments were conducted to investigate the effects of variati ons in talker characteristics, speaking rate, and overall amplitude on perceptual identification in normal-hearing young (NHY), normal-heari ng elderly (NHE), and hearing-impaired elderly (HIE) listeners. The th ree dimensions were selected because variations in voice characteristi cs and speaking rate affect features of speech signals that are import ant for word recognition while overall amplitude changes do not alter stimulus parameters that have direct effects on phonetic identificatio n. Thus, the studies were designed to examine how variations in both p honetically relevant and irrelevant stimulus dimensions affect speech processing in a number of different populations. Age differences, as i ndicated by greater effects of variability for the NHE compared with t he NHY listeners, were observed for mixed-talker and mixed-amplitude w ord lists. Effects of age-related hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for variations in speaking rate and talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization and selective attention may contribute to the reduced s peech understanding that is often reported for older adults. (C) 1997 Acoustical Society of America.