Effect of F2 intensity on identity of /u/ in degraded listening conditions.

The current study investigated the influence of the second formant (F2) intensity on vowel labeling along a /u/-/i/ continuum. Twenty-two listeners with normal-hearing (NH) sensitivity and 14 listeners with sensorineural hearing impairment (HI) were initially presented 2 stimuli for which the F2 intensity differed by 20 dB. The listeners were asked to label the 2 stimuli categorically as /u/ or /i/. After passing this criterion test, listeners were presented 9 stimuli whose F2 intensity varied within the 20-dB range. The 9 stimuli were evaluated in 3 listening conditions: in quiet, in the presence of a continuous speech spectrum noise (0-dB signal-to-noise ratio), and in the presence of reverberation (T = 1.0 s). The intensity manipulation altered the vowel labeling of NH listeners and yielded a differential effect in noise versus reverberation. Only 5 of the HI listeners were able to pass the criterion test, and of these 5, only 2 were able to label the 9 stimuli categorically. Results from HI listeners suggest problems in categorizing spectral shape.