EFFECTS OF STIMULUS VARIABILITY ON SPEECH-PERCEPTION IN LISTENERS WITH HEARING IMPAIRMENT

Traditional word-recognition tests typically use phonetically balanced (PB) word lists produced by one talker at one speaking rate. intellig ibility measures based on these tests may not adequately evaluate the perceptual processes used to perceive speech under more natural listen ing conditions involving many sources of stimulus variability The purp ose of this study was to examine the influence of stimulus variability and lexical difficulty on the speech-perception abilities of 17 adult s with mild-to-moderate hearing loss. The effects of stimulus variabil ity were studied by comparing word-identification performance in singl e-talker versus multiple-talker conditions and at different speaking r ates. Lexical difficulty was assessed by comparing recognition of ''ea sy'' words (i.e., words that occur frequently and have few phonemicall y similar neighbors) with ''hard'' words (i.e., words that occur infre quently and have many similar neighbors). Subjects also completed a 20 -item questionnaire to rate their speech understanding abilities in da ily listening situations. Both sources of stimulus variability produce d significant effects on speech intelligibility. Identification scores were poorer in the multiple-talker condition than in the single-talke r condition, and word-recognition performance decreased as speaking ra te increased. Lexical effects on speech intelligibility were also obse rved. Word-recognition performance was significantly higher For lexica lly easy words than lexically hard words. Finally, word-recognition pe rformance was correlated with scores on the self-report questionnaire rating speech understanding under natural listening conditions. The pa ttern of results suggest that perceptually robust speech-discriminatio n tests are able to assess several underlying aspects of speech percep tion in the laboratory and clinic that appear to generalize to conditi ons encountered in natural listening situations where the listener is Faced with many different sources of stimulus variability. That is, wo rd-recognition performance measured under conditions where the talker varied from trial to trial was better correlated with self-reports of listening ability than was performance in a single-talker condition wh ere variability was constrained.