Vowel and consonant confusions from spectrally manipulated stimuli designed to simulate poor cochlear implant electrode-neuron interfaces

Abstract

Suboptimal interfaces between cochlear implant (CI) electrodes and auditory neurons result in a loss or distortion of spectral information in specific frequency regions, which likely decreases CI users' speech identification performance. This study exploited speech acoustics to model regions of distorted CI frequency transmission to determine the perceptual consequences of suboptimal electrode-neuron interfaces. Normal hearing adults identified naturally spoken vowels and consonants after spectral information was manipulated through a noiseband vocoder: either (1) low-, middle-, or high-frequency regions of information were removed by zeroing the corresponding channel outputs, or (2) the same regions were distorted by splitting filter outputs to neighboring filters. These conditions simulated the detrimental effects of suboptimal CI electrode-neuron interfaces on spectral transmission. Vowel and consonant confusion patterns were analyzed with sequential information transmission, perceptual distance, and perceptual vowel space analyses. Results indicated that both types of spectral manipulation were equally destructive. Loss or distortion of frequency information produced similar effects on phoneme identification performance and confusion patterns. Consonant error patterns were consistently based on place of articulation. Vowel confusions showed that perceptions gravitated away from the degraded frequency region in a predictable manner, indicating that vowels can probe frequency-specific regions of spectral degradations.

Serial Recall Predicts Vocoded Sentence Recognition Across Spectral Resolutions

“…Sixty consonant-vowel-consonant words were selected for inclusion in word span lists based on two criteria. First, words were selected that only contain phonemes from a restricted set that minimized the occurrence of phonemes from the same phonetic confusion clusters (DiNino et al, 2016). Allowed phonemes were the consonants /w/, /d/, /p/, /s/, /ʃ/, /m/, /f/, /v/, /tʃ/, /h/ (initial phoneme only), and /z/ (final phoneme only) and the vowels /ӕ/, /ɑ/, /e/, /ε/, /i/, /o/, and /u/.…”

Age-Related Performance on Vowel Identification and the Spectral-temporally Modulated Ripple Test in Children With Normal Hearing and With Cochlear Implants

“…Vowels were naturally spoken by a female talker from the Pacific Northwest because regional dialect can influence speech identification performance ( Wright & Souza, 2012 ). Vowels were chosen as the stimuli for this study for several reasons: (a) Vowel identification performance in quiet matures at a younger age than for other speech stimuli ( Johnson, 2000 ); (b) vowels are simple units of speech and thus minimize the effects of children’s linguistic knowledge on recognition scores; and (c) while nonspectral cues can be utilized for vowel identification, one’s ability to resolve the formants, or spectral peaks, in the vowel sound is important for accurate vowel recognition (e.g., Boothroyd, Mulhearn, Gong, & Ostroff, 1996 ; DiNino, Wright, Winn, & Bierer, 2016 ; Shannon et al., 2002 ). Accordingly, vowels are appropriate speech stimuli for an investigation of spectral resolution and speech identification in children.…”

Predicting effects of hearing-instrument signal processing on consonant perception

“…The only substantial confusion that did not fall within the above-mentioned categories (/k/ confused with /f/) resulted from combining NLFC with INS, which suppresses sharp onsets and thus produces nonlinear changes over time. The CI processing applied in experiment 2 (DiNino et al, 2016) induced confusions within the categories voiced stops, unvoiced stops, fricatives, and nasals. According to Li et al (2010) and Li et al (2012), this again indicates a main perceptual effect of the spectral changes caused by the CI processing.…”

“…Furthermore, spectral resolution may be further degraded due to poor electrode-neuron interfaces-defined by regions of poor neural survival or a large distance between the CI electrodes and the auditory neurons (for review, see Bierer, 2010). DiNino et al (2016) investigated the effect of CI processing with poor electrode-neuron interfaces on the perception of consonants and vowels in NH listeners using VCV and consonant-vowel-consonant (CVC) syllables, respectively, that were noise-vocoded to simulate CI processing. A reference CI simulation condition using all available channels was considered along with conditions where low-, middle-, and high-frequency channels were either set to zero ("Zero"), simulating neural dead regions, or re-distributed to neighboring channels ("Split"), simulating poor electrode positioning.…”

“…Hearing-instrument signal processing, on the other hand, may lead to changed rather than masked consonant cues, inducing specific strong consonant confusions (cf. Schmitt et al, 2016;DiNino et al, 2016). A model that can account for such effects therefore needs to be sensitive not only to the presence of a consonant cue, but also to its perceptual similarity with other consonant cues.…”