Psychoacoustic tests for central auditory processing: normative data.

The comprehension of spoken language is based on the analysis of complex acoustic signals by the central auditory system, Direct relationships between gradual, spectrotemporal modifications of speech sounds and the impairment of the comprehension of such altered sounds have been found in many psychophysical studies. Thus, it is reasonable to assume that deficits in the understanding of speech seen in patients with acquired brain lesions may, to a certain degree, result from impaired central processing of acoustic signals. We report normative data collected from 94 young normal-hearing subjects on a battery of psychoacoustic tests designed to evaluate signal processing at different levels of the central auditory system. Monaural pure tone thresholds were used to evaluate the performance of peripheral hearing. The integrity of auditory brainstem processing was evaluated by quantifying masking level difference (MLD) values and gap detection (GD) thresholds. Three monaural speech tests (time-compressed speech [CS], filtered speech [FS] and speech in noise [SIN]) were conducted to evaluate the processing of distorted speech materials by cortical auditory processing mechanisms. Evaluating performance of naïve, young normal-hearing subjects, as we did here, is indispensable for (a) evaluating the effectiveness of potential tests, (b) evaluating their suitability for the examination of patients, and (c) the revision and further development of central auditory tests.