Effects of age on melody and timbre perception in simulations of electro-acoustic and cochlear-implant hearing.

OBJECTIVES: Recent evidence suggests that age might affect the ability of listeners to process fundamental frequency cues in speech, and that this difficulty might impact the ability of older listeners to use and combine envelope and fine structure cues available in simulations of electro-acoustic and cochlear-implant hearing. The purpose of this article is to examine whether this difficulty extends to music. Specially, this study focuses on whether older listeners have a decreased ability to use and combine different types of cues in the perception of melody and timbre.
DESIGN: A group of older listeners with normal to near-normal hearing and a group of younger listeners with normal hearing participated in the melody and timbre recognition tasks of the University of Washington Clinical Assessment of Music Perception test. The recognition tasks were completed for five different processing conditions: (1) an unprocessed condition; (2) an eight-channel vocoding condition that simulated a traditional cochlear implant and contained temporal envelope cues; (3) a simulation of electro-acoustic stimulation (sEAS) that included a low-pass acoustic component and high-pass vocoded portion, and which provided fine structure and envelope cues; (4) a condition that included only the low-pass acoustic portion of the sEAS; and (5) a condition that included only the high-frequency vocoded portion of the sEAS stimulus.
RESULTS: Melody recognition was excellent for both younger and older listeners in the conditions containing the unprocessed stimuli, the full sEAS stimuli, and the low-pass sEAS stimuli. Melody recognition was significantly worse in the cochlear-implant simulation condition, especially for the older group of listeners. Performance on the timbre task was highest for the unprocessed condition, and progressively decreased for the sEAS and cochlear-implant simulation conditions. Compared with younger listeners, older listeners had significantly poorer timbre recognition for all processing conditions. For melody recognition, the unprocessed low-frequency portion of the sEAS stimulus was the primary factor determining improved performance in the sEAS condition compared with the cochlear-implant simulation. For timbre recognition, both the unprocessed low-frequency and high-frequency vocoded portions of the sEAS stimulus contributed to sEAS improvement in the younger group. In contrast, most listeners in the older group were not able to take advantage of the high-frequency vocoded portion of the sEAS stimulus for timbre recognition.
CONCLUSIONS: The results of this simulation study support the idea that older listeners will have diminished timbre and melody perception in traditional cochlear-implant listening due to degraded envelope processing. The findings also suggest that music perception by older listeners with cochlear implants will be improved with the addition of low-frequency residual hearing. However, these improvements might not be comparable for all dimensions of music perception. That is, more improvement might be evident for tasks that rely primarily on the low-frequency portion of the electro-acoustic stimulus (e.g., melody recognition), and less improvement might be evident in situations that require across-frequency integration of cues (e.g., timbre perception).