The recognition of isolated words and words in sentences: Individual variability in the use of sentence context

Estimates of the ability to make use of sentence context in 34 postlinguall y hearing-impaired (HI) individuals were obtained using formulas developed by Boothroyd and Nittrouer [Boothroyd and Nittrouer, J. Acoust. Sec. Am. 84 , 101-114 (1988)] which relate scores for isolated words to words in meanin gful sentences. Sentence materials were constructed by concatenating digiti zed productions of isolated words to ensure physical equivalence among the test items in the two conditions. Isolated words and words in sentences wer e tested at three levels of intelligibility (targeting 29%, 50%, and 79% co rrect). Thus, for each subject, three estimates of context ability, or k fa ctors, were obtained. In addition, auditory, visual, and auditory-visual se ntence recognition was evaluated using natural productions of sentence mate rials. Two main questions were addressed: (1) Is context ability constant f or speech materials produced with different degrees of clarity? and (2) Wha t are the relations between individual estimates of k and sentence recognit ion as a function of presentation modality? Results showed that estimates o f k were not constant across different levels of intelligibility: k was gre ater for the more degraded condition relative to conditions of higher word intelligibility. Estimates of k also were influenced strongly by the test o rder of isolated words and words in sentences. That is, prior exposure to w ords in sentences improved later recognition of the same words when present ed in isolation (and vice versa), even though the 1500 key words comprising the test materials were presented under degraded (filtered) conditions wit hout feedback. The impact of this order effect was to reduce individual est imates of k fur subjects exposed to sentence materials first and to increas e estimates of k for subjects exposed to isolated words first. Finally, sig nificant relationships were found between individual k scores and sentence recognition scores in all three presentation modalities, suggesting that k is a useful measure of individual differences in the ability to use sentenc e context. (C) 2000 Acoustical Society of America. [S0001-4966(00)03802-9].