Effects of contextual cues on speech recognition in simulated electric-acoustic stimulation

Abstract

Low-frequency acoustic cues have shown to improve speech perception in cochlear-implant listeners. However, the mechanisms underlying this benefit are still not well understood. This study investigated the extent to which low-frequency cues can facilitate listeners' use of linguistic knowledge in simulated electric-acoustic stimulation (EAS). Experiment 1 examined differences in the magnitude of EAS benefit at the phoneme, word, and sentence levels. Speech materials were processed via noise-channel vocoding and lowpass (LP) filtering. The amount of spectral degradation in the vocoder speech was varied by applying different numbers of vocoder channels. Normal-hearing listeners were tested on vocoder-alone, LP-alone, and vocoder þ LP conditions. Experiment 2 further examined factors that underlie the context effect on EAS benefit at the sentence level by limiting the low-frequency cues to temporal envelope and periodicity (AM þ FM). Results showed that EAS benefit was greater for higher-context than for lower-context speech materials even when the LP ear received only low-frequency AM þ FM cues. Possible explanations for the greater EAS benefit observed with higher-context materials may lie in the interplay between perceptual and expectation-driven processes for EAS speech recognition, and/or the band-importance functions for different types of speech materials.

The role of continuous low-frequency harmonicity cues for interrupted speech perception in bimodal hearing

“…Considered in isolation, this finding suggests that continuous periodicity/harmonicity information carried in the cLPHC can support improved identification of word and syllable boundaries (i.e., enhanced segmentation), as suggested previously by Kong et al (2015). However, the data obtained in experiment 1 with gated vocoder speech showed that similar bimodal benefit was achieved when the low-frequency ear received noise-filled LPHCs (gV þ nfLPHC condition) as when it received continuous LPHCs (gV þ cLPHC condition).…”

“…Kong et al (2015) showed that simulated bimodal listeners were able to achieve significant amounts of bimodal benefit when receiving continuous vocoded sentences in one ear and a continuous LPHC in the other. Given that all speech materials were presented in quiet, they attributed the observed bimodal benefit to improved speech segmentation (i.e., enhanced definition of syllable and word boundaries) when robust harmonicity cues were present in the bimodal listening condition.…”

“…Percentage-point gain provides an intuitive measure of bimodal benefit, and has been used in a number of previous studies (e.g., Kong et al, 2005;Kong and Carlyon, 2007;Başkent and Chatterjee, 2010;Başkent, 2012;Kong et al, 2015). It was appropriate for the present study because a single measure of baseline performance (i.e., the gV listening condition) was used for all bimodal comparisons (Kong et al, 2015).…”

“…Stimuli were City University of New York (CUNY) sentences (Boothroyd et al, 1985) recorded by an adult female speaker of standard American English in a conversational speaking style, as described by Kong et al (2015). The CUNY sentence corpus consists of 60 lists sentences, and each list includes 12 sentences.…”

“…By integrating the available speech cues across ears, the listener may be able to improve performance relative to performance with the CI alone (Kong and Braida, 2011;Sheffield and Zeng, 2012;Visram et al, 2012a;Yang and Zeng, 2013). Second, harmonicity cues contained in the low-frequency acoustic signal may improve listeners' ability to segment syllable, word, and phrase boundaries, thereby helping them to accurately decode spectrally degraded signals from the CI ear (Spitzer et al, 2009;Zhang et al, 2010;Kong et al, 2015). As discussed by Li and Loizou (2008) and Dorman and Gifford (2008), low-frequency fine-structure cues improve listeners' access to robust acoustic landmarks (Stevens, 2002), such as the onset of voicing, that mark syllable structure and word boundaries.…”