Temporal cues and the effect of their enhancement on speech perception in older adults – A scoping review

Abstract

Temporal envelope is a low frequency amplitude modulation conveying segmental and suprasegmental information during speech perception. Unfortunately, we seldom find ourselves in completely quiet listening environments and noise, commonly found in the surrounding environment, obscures both the fine structure cues and partly the temporal envelope cues in speech. Available temporal content of speech emanating from noise is often enough to convey required information in normal hearing individuals. However, the case is different in older adults (with and without hearing loss) who lack such capabilities due to the impairment in temporal processing. This calls attention of a researcher to delineate the importance of temporal enhancement of speech in improving speech perception. There are many temporal envelope strategies available in the literature, but each one has its own lacunae. An envelope enhancement by a deep band modulation (DBM) is found to be beneficial for those individuals who have had a temporal processing impairment. The reason could be attributed to the 15 dB enhancement in the temporal envelope bandwidth between 3 and 30 Hz, extracted from each channel, which significantly increases the modulation depth such that masking of a consonant by a vowel is minimized. Additionally, output of deep band modulated speech is rescaled such that its duration increases and it provides relatively easy access to the word of the lexicon. Thus, in the near future, with more experiments related to DBM algorithm, it can be utilized in the rehabilitative devices to lessen the impact of the temporal processing impairment.

Brainstem correlates of concurrent speech identification in adverse listening conditions

“…Noise tends to obscure amplitude modulations in speech that are essential for its comprehension (Bidelman, 2016; Shannon et al, 1995; Swaminathan and Heinz, 2012). In contrast, in cases of speech-on-speech masking, listeners can better utilize spectral dips for perception, resulting in less effective masking than continuous noise (Peters et al, 1998; Shetty, 2016). FFR changes related to speech-on-speech masking and SNR were evident in both the time and frequency domain results, consistent with previous studies (Bidelman and Krishnan, 2010; Bidelman, 2016; Hornickel et al, 2011; Song et al, 2011; Tierney et al, 2011).…”

Model-based hearing-enhancement strategies for cochlear synaptopathy pathologies

“…At the same time, the distortion of speech after processing could also be a reason for the individual differences and small benefits in SI scores. Although our algorithms were optimised purely on the basis of the simulated outcomes of a biophysical model [50], additional signal-processing techniques could be applied after the optimisation procedure to minimise the negative effects that envelope processing might introduce (e.g., [37,39,44,47,93,94]). The presented algorithms rely on instantaneous processing of the temporal envelope (RMS window of <1 ms), which has been argued to lead to non-linear distortion and poor sound quality in dynamic-range compression [17,32,34,35,37,[94][95][96][97].…”

“…Acoustic modifications of the speech-envelope shape and periodicity can improve SI [18,[32][33][34][35][36][37], especially in connection with hearing through cochlear implants [38][39][40][41][42][43]. Several studies have shown that envelope enhancement can be beneficial for speech recognition in individuals with temporal processing deficits [22,36,[44][45][46][47][48]. Here, we go beyond these conventional approaches to develop a model-based type of auditory envelope processing that operates directly on the signal waveform to counteract the functional consequences associated with CS.…”

Does amplitude compression help or hinder attentional neural speech tracking?

“…It reduces the amplitude modulation depth, and alters the envelope shape, and thus alters the intelligibility-relevant temporal cues contained in speech (Stone & Moore, 1992). The envelope of speech is thus not just a simple acoustic feature of speech but also associated with speech comprehension (Poeppel & Assaneo, 2020; Shetty, 2016).…”