SUBJECTIVE JUDGMENTS OF CLARITY AND INTELLIGIBILITY FOR FILTERED STIMULI WITH EQUIVALENT SPEECH-INTELLIGIBILITY INDEX PREDICTIONS

The purpose of this investigation was to determine whether subjective judgments of clarity or intelligibility would be rated equally among c onditions in which speech was equated for predicted intelligibility (u sing the Speech Intelligibility Index, SII) but varied in bandwidth. T wenty listeners with normal hearing rated clarity and intelligibility for sentence material (Hearing In Noise Test) in speech-shaped noise a t six paired low- and high-pass Filtered conditions in which SII was e quated for each pair. For three paired conditions, predicted intelligi bility increased as SII increased monotonically (0.3, 0.4, 0.5). In th e remaining paired conditions, SII continued to increase monotonically (0.6, 0.7, 0.8) but predicted intelligibility was held at a maximal l evel (greater than or equal to 95%). Predicted intelligibility was est imated from the transfer function relating SII to speech recognition s cores determined in preliminary experiments. Differences in ratings be tween paired low-and high-pass filtered sentences did not reach statis tical significance for either clarity or intelligibility, indicating t hat the spectral differences at equivalent Sits did not influence the judgments for either of the two dimensions. For conditions in which pr edicted intelligibility increased, both clarity and intelligibility ra tings increased in a similar manner. For conditions in which predicted intelligibility was maximized, intelligibility ratings remained the s ame statistically across conditions while clarity ratings changed mode stly. Although high correlations were observed between clarity and int elligibility ratings, intelligibility ratings were consistently higher than clarify ratings For comparable conditions. The results indicated that listeners with normal hearing produced clarity and intelligibili ty ratings for the same speech material and experimental conditions th at were highly related but differed in magnitude. Caution is required when substituting clarity For intelligibility.