Forward Digit Span and Word Familiarity Do Not Correlate With Differences in Speech Recognition in Individuals With Cochlear Implants After Accounting for Auditory Resolution

Abstract

Purpose In individuals with cochlear implants, speech recognition is not associated with tests of working memory that primarily reflect storage, such as forward digit span. In contrast, our previous work found that vocoded speech recognition in individuals with normal hearing was correlated with performance on a forward digit span task. A possible explanation for this difference across groups is that variability in auditory resolution across individuals with cochlear implants could conceal the true relationship between speech and memory tasks. Here, our goal was to determine if performance on forward digit span and speech recognition tasks are correlated in individuals with cochlear implants after controlling for individual differences in auditory resolution. Method We measured sentence recognition ability in 20 individuals with cochlear implants with Perceptually Robust English Sentence Test Open-set sentences. Spectral and temporal modulation detection tasks were used to assess individual differences in auditory resolution, auditory forward digit span was used to assess working memory storage, and self-reported word familiarity was used to assess vocabulary. Results Individual differences in speech recognition were predicted by spectral and temporal resolution. A correlation was found between forward digit span and speech recognition, but this correlation was not significant after controlling for spectral and temporal resolution. No relationship was found between word familiarity and speech recognition. Forward digit span performance was not associated with individual differences in auditory resolution. Conclusions Our findings support the idea that sentence recognition in individuals with cochlear implants is primarily limited by individual differences in working memory processing, not storage. Studies examining the relationship between speech and memory should control for individual differences in auditory resolution.

Figure 1.

Association between PRESTO sentence recognition and predictor tasks. The top four panels show the relationship between PRESTO accuracy and performance on each predictor task, and the bottom two panels show the relationship between digit span and word familiarity task performance with residual PRESTO sentence recognition after factoring out spectral and temporal modulation detection thresholds. Each point represents results from one participant. Correlation coefficients and p values for simple linear correlations are provided in each panel. Lines show the standard major axis regression fit (Legendre, 2013) across individuals for significant relationships in Table 3. PRESTO = Perceptually Robust English Sentence Test Open-set.

Figure 2.

Digit span performance across participants. Each thin line represents the proportion of digits that were recalled in the correct position across all trials at each list length for one individual. The thick black line shows the average performance across individuals. The thick gray line shows average performance of young adults with normal hearing averaged across vocoder listening conditions in Bosen and Barry (2020).

Figure 3.

Association between digit span and other predictor tasks. Each point represents results from one participant. Correlation coefficients and p values for simple linear correlations are provided in each panel.