| The heterogeneity of speech perception abilities of persons with hearing loss, despite similar pure-tone thresholds, has been demonstrated in auditory research (Plomp, 1978, 1986; Thibodeau & Scott, 2002). This area of research was most recently focused on the ability of listeners with high-frequency hearing loss (HFHL) to make use of amplified high-frequency speech cues (Hogan & Turner, 1998; Turner & Cummings, 1999; Turner & Henry, 2002). Some listeners with HFHL showed limited or negative benefit from high-frequency amplification, which brought into question the efficacy of attempting to provide maximum audibility for persons with HFHL. This was important to note as commercially available Digital Signal Processing Hearing Instruments (DSPHI) were designed to provide multiple methods of high-frequency adjustment including frequency band shaping, modifiable compression parameters and selectable levels of channel specific noise reduction. In the current study a more externally-valid methodology was used compared to previous research. The ability for listeners with HFHL to use high-frequency speech cues was measured via the advanced capabilities of a custom fitted DSPHI. A spectrally-based modification of an adaptive sentence test, the Hearing In Noise Test (HINT) (Nilsson, Soli, & Sullivan, 1994), was assessed as a tool that quantified the benefit a listener received from high-frequency speech cues. This modification was called the High-Frequency HINT (HFHINT). Results from Experiment 1 on a group of 20 listeners with normal hearing indicated that the HFHINT was more sensitive to changes in high-frequency speech cues compared to the standard HINT. Experiment 2 consisted of a group of 10 listeners with HFHL. Subjects were fitted with a commercially available DSPHI programmed to four different conditions that systematically reduced the amount of high-frequency information. Sentence thresholds in noise obtained via the HFHINT indicated that listeners with moderate-to-severe hearing loss on average used amplified high-frequency speech cues, although this ability varied. The HFHINT was sensitive enough to determine which listeners with HFHL were able to effectively use amplified high-frequency speech information, and which were not. The overall results and implications from this study were discussed in relationship to the candidacy and fitting of DSPHI and cochlear implant hybrids. |
