Lexical-Access Ability and Cognitive Predictors of Speech Recognition in Noise in Adult Cochlear Implant Users

Abstract

Not all of the variance in speech-recognition performance of cochlear implant (CI) users can be explained by biographic and auditory factors. In normal-hearing listeners, linguistic and cognitive factors determine most of speech-in-noise performance. The current study explored specifically the influence of visually measured lexical-access ability compared with other cognitive factors on speech recognition of 24 postlingually deafened CI users. Speech-recognition performance was measured with monosyllables in quiet (consonant-vowel-consonant [CVC]), sentences-in-noise (SIN), and digit-triplets in noise (DIN). In addition to a composite variable of lexical-access ability (LA), measured with a lexical-decision test (LDT) and word-naming task, vocabulary size, working-memory capacity (Reading Span test [RSpan]), and a visual analogue of the SIN test (text reception threshold test) were measured. The DIN test was used to correct for auditory factors in SIN thresholds by taking the difference between SIN and DIN: SRT_diff. Correlation analyses revealed that duration of hearing loss (dHL) was related to SIN thresholds. Better working-memory capacity was related to SIN and SRT_diff scores. LDT reaction time was positively correlated with SRT_diff scores. No significant relationships were found for CVC or DIN scores with the predictor variables. Regression analyses showed that together with dHL, RSpan explained 55% of the variance in SIN thresholds. When controlling for auditory performance, LA, LDT, and RSpan separately explained, together with dHL, respectively 37%, 36%, and 46% of the variance in SRT_diff outcome. The results suggest that poor verbal working-memory capacity and to a lesser extent poor lexical-access ability limit speech-recognition ability in listeners with a CI.

Keywords: cochlear implants; lexical access; linguistic skills; speech-in-noise recognition; working memory.

Figure 1.

Speech reception thresholds (left axis) for sentences (SIN) and digit-triplets (DIN) in stationary noise and % phonemes correct (right axis) for monosyllables in quiet (CVC). Participants were arranged in order of DIN threshold (from best to poorest) and divided into two performance groups. SRT = speech reception threshold; SNR = signal-to-noise ratio; DIN = digits-in-noise; SIN = sentences-in-noise; CVC = consonant-vowel-consonant.

Figure 2.

Relations between working-memory capacity (RSpan), lexical-access ability with a composite measure (LA), and with a lexical-decision test (LDT) with sentence-in-noise recognition (SIN) and the derived variable SRT_diff (difference between sentence-in-noise recognition and digits-in-noise recognition). Open symbols reflect the unreliable SIN results of listeners in Group 2. Lines represent significant correlations. SRT = speech reception threshold; SNR = signal-to-noise ratio; SIN = sentences-in-noise; LA = lexical access; RSpan = Reading Span test.

Figure 3.

Difference in speech reception threshold for sentences-in-noise and digits-in-noise (SRT_diff) for cochlear implant users (diamonds) together with the normal-hearing (NH) data of listeners with various levels of linguistic skills and nonnative listeners of Kaandorp et al. (2016; circles). Lines represent regression lines for both groups (black dashed for CI users, gray solid for NH listeners). The area between the vertical dashed lines represents the range of native NH listeners. SRT = Speech Reception Threshold; SNR = signal-to-noise ratio; CI = cochlear implant.