Title: "Effects of aging on dynamic and static encoding of speech processing in quiet and noise"
Speaker: Alex Presacco, Department of Hearing and Speech Sciences
Date: Wednesday, March 12; 12-1 PM
Room: LeFrak Hall Room 0135
Abstract:
Older adults frequently experience problems understanding speech, despite having good hearing. Increasing audibility with hearing aids helps only to a certain extent, as their use cannot restore the temporal precision degraded by aging. Decreased precision may lead to neural timing delays and a disadvantage in processing the rapid acoustic changes in speech. This temporal deficit may arise from age-related changes in inhibitory neurotransmitter levels and delayed neural recovery. The auditory brainstem response to complex sounds (cABR), a scalp-recorded electrical potential, is known for its ability to capture precise neural synchrony within subcortical auditory nuclei. In the first study, we compared subcortical responses in younger and older adults with normal hearing to the speech syllables /da/ and /a/, hypothesizing that aging affects the timing of dynamic rather than static encoding of speech components. The responses of older adults are significantly delayed, but only for the transient region of the /da/, not the /a/, which is static throughout its length. Amplitude and phase dissimilarities were also noted between the two groups. In a second study, we compared subcortical responses in younger and older adults with normal hearing to the consonant-vowel syllable [da] presented in quiet and noise, hypothesizing that, different from younger adults, the FFR in older adults shows no significant differences between quiet and noise conditions due to the fact that their temporal precision is already compromised. The QuickSIN was also used to objectively measure understanding of speech in noise. Older adults show no significant differences between the FFR envelope and fine structure in quiet and noise. The phase-locking factor was calculated to estimate at which frequencies these differences emerged. The results suggested that the most remarkable differences between younger and older adults were not localized at the fundamental frequency (100 Hz), but rather at the higher harmonics. The QuickSIN also showed significant differences (p < 0.01) between younger and older adults.
Overall, these results confirm the hypothesis that older adults’ timing deficits occur in response to the dynamic rather than static components of the speech signal. The lack of temporal precision at the brainstem level may be one of the key factors underlying their problems in understanding speech in noise.
