Frequency glide discrimination in the F2 region by normal-hearing and hearing-impaired listeners

The dynamic formant transitions present within consonant-vowel and vowel-consonant utterances may be poorly processed by hearing-impaired (HI) listeners and may, as a result, provide reduced segmental information to these listeners. Both the brief durations and rapid spectral change associated with these transitions have been proposed as contributing to these deficits in processing. To investigate HI listeners' processing of transitional stimuli, six HI and six normal-hearing (NH) listeners were asked to discriminate between frequency glides patterned after second formant transitions in English CV syllables. The influences of glide duration, rate, and frequency extent were examined for each group in quiet and in broadband noise. Reductions in glide duration and the presence of noise each led to significant increases in frequency difference limens for glide onset. The magnitudes of these effects were similar across groups, thereby failing to show increased susceptibility to noise or greater deficits in dealing with brief stimuli on the part of HI listeners. Contrary to the expectation that HI listeners would show greatest deficits (relative to the NH group) for the most rapidly changing glides, the only significant group differences were observed for gradual glides of limited frequency extent. This latter finding is discussed in terms of sensitivity to "cochlear dispersion" cues [Porter et al., J. Acoust. Soc. Am. 90, 1298-1308 (1991)]. It is hypothesized that HI listeners may not process these cues as effectively as NH listeners, perhaps as a result of impaired frequency selectivity.