Effects of high presentation levels on recognition of low- and high-frequency speech

Speech recognition accuracy decreases when presentation levels are raised above moderate levels. This rollover effect at high levels has generally been viewed as a broadband phenomenon, influencing low- and high-frequency processing similarly. In the current study, listeners with normal hearing identified lowpass and highpass sentences at a range of presentation levels to determine whether rollover effects might be greater in either region. Recognition scores showed larger and more consistent decreases at high levels (i.e., greater rollover) for high-frequency speech materials. The results are consistent with both physiological and psychoacoustic data suggesting that cochlear processing shows greater level dependence in basal regions tuned to high frequencies than apical, low- frequency regions. Predictions of speech intelligibility by methods such as the Speech Intelligibility Index [ANSI, 1997] may be improved if the frequency-dependence of rollover is considered. (C) 2003 Acoustical Society of America.