Age-Related Differences in the Processing of Temporal Envelope and Spectral Cues in a Speech Segment

Abstract

OBJECTIVE As people age, they experience reduced temporal processing abilities. This results in poorer ability to understand speech, particularly for degraded input signals. Cochlear implants (CIs) convey speech information via the temporal envelopes of a spectrally degraded input signal. Because there is an increasing number of older CI users, there is a need to understand how temporal processing changes with age. Therefore, the goal of this study was to quantify age-related reduction in temporal processing abilities when attempting to discriminate words based on temporal envelope information from spectrally degraded signals. DESIGN Younger normal-hearing (YNH) and older normal-hearing (ONH) participants were presented a continuum of speech tokens that varied in silence duration between phonemes (0 to 60 ms in 10-ms steps), and were asked to identify whether the stimulus was perceived more as the word “Dish” or “Ditch.” Stimuli were vocoded using tonal carriers. The number of channels (1, 2, 4, 8, 16, and unprocessed) and temporal envelope low-pass filter cutoff frequency (50 and 400 Hz) were systematically varied. RESULTS For the unprocessed conditions, the YNH participants perceived the word Ditch for smaller silence durations than the ONH participants, indicating that aging affects temporal processing abilities. There was no difference in performance between the unprocessed and 16-channel, 400-Hz vocoded stimuli. Decreasing the number of spectral channels caused decreased ability to distinguish Dish and Ditch. Decreasing the envelope cutoff frequency also caused decreased ability to distinguish Dish and Ditch. Nevertheless, the overall pattern of results revealed that reductions in spectral and temporal information had a relatively larger effect on the ONH participants compared to the YNH participants. CONCLUSION Aging reduces the ability to utilize brief temporal cues in speech segments. Reducing spectral information – as occurs in a channel vocoder and in CI speech processing strategies – forces participants to use temporal envelope information; however, older participants are less capable of utilizing this information. These results suggest that providing as much spectral and temporal speech information as possible would benefit older CI users relatively more than younger CI users. In addition, the present findings help set expectations of clinical outcomes for speech understanding performance by adult CI users as a function of age.

Age effects on perceptual restoration of degraded interrupted sentences

“…No research has specifically analyzed the effects of NBinterrupted vocoded speech and the PR effect in ONH listeners. ONH listeners generally show slower temporal processing for complex stimuli like speech (Goupell et al, 2017;Fitzgibbons and Gordon-Salant, 1996) and less precise encoding of the temporal properties of speech subcortically (Anderson et al, 2012). When speech is degraded by a vocoder to simulate aspects of CI processing, spectral resolution is reduced and temporal envelopes of the signal must be relied upon for accurate speech perception (Shannon et al, 1995).…”

“…Slower temporal processing and less precise temporal encoding associated with aging may have influenced how ONH participants perceived and utilized NB interruptions in the present study. Older participants have less ability to perceive and encode sudden temporal changes in the speech signal (Anderson et al, 2012;Fitzgibbons and Gordon-Salant, 1996;Goupell et al, 2017), so the perception of the rapid changes between speech and NB interruptions may have resulted in a stronger, more fused percept of the two stimuli. A more fused percept would result in a stronger auditory illusion of the speech continuing through the noise, and therefore a stronger PR effect.…”

“…Vocoding reduces the amount of spectral information in the speech signal, while mostly preserving temporal envelope information (Shannon et al, 1995). PR with vocoded speech might therefore depend on one's ability to restore temporal envelopes, the processing of which is less efficient in ONH participants (Goupell et al, 2017). LME model analyses revealed that PR benefits in ONH participants were not affected by spectral resolution, as the interaction of age group, number of channels, and interruption type was not significant and was not included in the models (Tables IV and V).…”

Contributions to Speech-Cue Weighting in Older Adults With Impaired Hearing

“…Even listeners with substantive impairments such as listeners with auditory neuropathy spectrum disorder (Wang et al, 2016) or who use auditory brainstem implants (Azadpour & McKay, 2014) have relatively good envelope perception. Recent data suggest that the relative weight placed on envelope (vs. spectral cues) may change with age but not with hearing loss per se (Goupell et al, 2017;Toscano & Lansing, 2019).…”

Memory Span for Spoken Digits in Adults With Cochlear Implants or Typical Hearing: Effects of Age and Identification Ability

“…The sine-vocoded stimuli were created using MATLAB routines. The original stimuli were bandpass filtered (thirdorder Butterworth, using the "filtfilt" forward-and-reverse MATLAB filtering function) to minimize temporal distortion (e.g., Goupell et al, 2017) into four or eight contiguous channels. The corner frequencies of these filters spanned 200 to 5000 Hz and were logarithmically spaced (see Figure 1 for center frequencies).…”