| This series of experiments evaluated the effects of nonlinear frequency compression (NFC) hearing aid processing on speech recognition in listeners with sloping high-frequency hearing impairment, with focus given to the time course and magnitude of perceptual acclimatization. The first experiment evaluated prototype NFC signal processing; this multichannel technology was applied to the high-frequency region of speech using individualized NFC programming features. Participants included 13 adult and 11 child listeners with sloping, high-frequency hearing impairment. Multiple outcome measures were repeated using a withdrawal design. These included speech sound detection, speech recognition, and self-reported preference measures. Group level results provide evidence of significant improvement of consonant and plural recognition with active NFC; vowel recognition did not change significantly. Analysis of individual results allowed for exploration of factors contributing to benefit received from NFC processing. Findings suggest that NFC processing can improve high-frequency speech detection and speech recognition ability for adult and child listeners. Variability in individual outcomes related to factors such as degree and configuration of hearing loss, age of participant, and type of outcome measure.;The third experiment evaluated the time course and magnitude of perceptual acclimatization to newly audible high-frequency sounds in 6 child listeners. This included a well-controlled adaptation period to NFC processing (M = 16 weeks), and a high-frequency focused outcome measurement battery including measures of speech detection, discrimination and recognition. Results suggest large individual variance in both the time course and magnitude of benefit change. A longer acclimatization period was needed to achieve significant NFC benefit for recognition based tasks, when compared to detection based tasks. Initial benefit and/or decrement with NFC were observed for some cases. For some individuals, a specific period of acclimatization time (i.e., 6 to 8 weeks) was needed prior to observing significant NFC benefit. Acclimatization effects may have extended beyond 16 weeks for some individuals. Furthermore, the listeners with steeply sloping hearing loss required a longer acclimatization period prior to demonstrating NFC benefit on speech recognition tasks; this likely related to time needed to learn novel high-frequency speech cues.;Keywords: Hearing, Hearing Impairment, Hearing Aids, Children, Speech Perception, Acclimatization, Nonlinear Frequency Compression, High Frequency.;The second experiment re-evaluated NFC benefit in 11 child listeners, comparing results obtained with prototype processing to those obtained with the commercial product. The participants were recruited from experiment 1, and wore the prototype hearing aids for at least 1 year (M = 2.03 years) prior to being refitted with commercial devices. Results were comparable to those previously reported; children with lower speech recognition/detection scores using hearing aids without NFC benefited most with active NFC. Some listeners show the additional effect of continued improvement with NFC over time, due to maturation, acclimatization effects, or both. |
