Lauren Wilson of HESP UMD will be defending her Honor's Thesis on the "Effects of aging on identification of spectrally degraded and frequency-shifted digits in normal-hearing listeners". 

Abstract: 

The ability to accurately understand speech is impacted by several age-related factors such as hearing loss and possibly neural plasticity. Cochlear-implant (CI) users often have greater difficulty understanding speech than normal-hearing (NH) listeners, even when the NH listeners are presented simulated CI processed (i.e., vocoded) speech. The purpose of this study was to determine if the age-related declines in understanding frequency-shifted speech in NH listeners is the result of high-frequency hearing loss or declines in brain plasticity. Younger, middle-aged, and older NH listeners were tested in this study, 10 in each group. They were presented digit stimuli that had been vocoded with different numbers of channels (4, 6, and 8) and frequency shifts (0, 1, and 2 channels). When shifted, the digits had frequency information above 4000 Hz, where middle-aged and older listeners had relatively higher thresholds. The channels shifted to a higher frequency than 4000 Hz were either kept or dropped. Using these stimuli, we hypothesized that age-related declines in understanding shifted vocoded speech resulted from lack of encoding of higher frequencies and/or a decline in neural plasticity. We found that older listeners can become as good as younger listeners at understanding vocoded with repeated exposure when listening to a closed set, such as digits. After removing listeners with previous exposure, there were no effects of age, which contradicts the previous literature that suggests older adults are worse at understanding frequency-shifted speech. This may have been a result of a lack of statistical power or changes in the stimuli or procedure. Finally, there was no significant correlation between thresholds at 8 and 12 kHz and shifted vocoded speech understanding, providing little evidence that poorer shifted vocoded speech understanding can be explained by higher frequency hearing loss. This study suggests future directions for understanding older listeners ability to relearn speech sounds, which ultimately informs how older CI listeners may perform.