Speech audiometry in noise-exposed workers: The SRT-PTA relationship revisited

The speech recognition threshold (SRT) is believed to be related primarily to the pure-tone average (PTA) and the steepness of the hearing loss. Howev er, there are indications that it may also be influenced by perceptual or c ognitive-linguistic factors, or both, such as meaningfulness of the speech stimuli. The purpose of the present study was to ascertain the corresponden ce between SRT and PTA in noise-exposed workers with various degrees of spe ech recognition threshold shift in noise. To this end, a total of 807 SRTs and PTAs collected from fluent speakers of Quebec French noise-exposed work ers were compared. Measurements of context effects on speech recognition we re taken based on a general hypothesis that they should be facilitating pho neme or word restoration in conditions of high stimulus uncertainty as pres ent in SRT assessment, thus acting to confound the SRT-PTA relationship. Us ing principal components analysis, we found a significant effect not only o f low-frequency hearing sensitivity but language context effects on SRT. Af ter a correction was introduced to partial out these linguistic context eff ects, correlations between SRT and PTA increased but they were lower than p redicted. In a related treatment analysis, we found a large number of obser vations (230 out of 807) where SRTs were more sensitive than PTAs by a fact or of 8 to 16 dB. This was the case even though correlations between the tw o measurements were within the range commonly advocated in the field of cli nical audiology (0.85-0.95). This was interpreted as a sign of phonological and lexical context effects on the speech recognition task actually used b y individual subjects to facilitate speech understanding, to the point perh aps of making it as simple as the detection of pure tones.