The effects of stimulus modality, task complexity, and cuing on working memory and the relationship with speech recognition in older cochlear implant users

Introduction: The role of working memory (WM) in speech recognition of older cochlear implant (CI) users remains unclear. This study 1) examined the effects of aging and CI on WM performance across different modalities (auditory vs. visual) and cuing conditions, and 2) assessed how specific WM measures relate to sentence and word recognition in noise. Method: Fourteen Older CI users, 12 Older acoustic-hearing (AH) listeners with age-appropriate hearing loss, and 15 Young normal-hearing (NH) listeners were tested. Participants completed two simple span tasks (auditory digit and visual letter span), two complex WM tasks (reading span and cued-modality WM with simultaneously presented auditory digits and visual letters), and two speech recognition tasks (sentence and word recognition in speech-babble noise). Results: The groups showed similar simple span performance, except that Older CI users had lower auditory digit span than Young NH listeners. Both older groups had similar reading span performance, but scored significantly lower than Young NH listeners, indicating age-related declines in attentional and phonological processing. A similar group effect was observed in the cued-modality WM task. All groups showed higher recall for auditory digits than for visual letters and the advantage was most evident without modality cuing. All groups displayed greater cuing benefits for visual recall than for auditory recall, suggesting that participants consistently allocated more attention to auditory stimuli regardless of cuing. For Older CI users, after controlling for the previously reported spectral resolution, auditory-uncued WM performance was significantly correlated with word recognition but not sentence recognition. Conclusions: Complex WM was significantly affected by aging but not by CI. Neither aging nor CI significantly affected modality cuing benefits in the WM task. For Older CI users, complex auditory WM with attentional control may better reflect the cognitive load of speech recognition in noise than simple span or complex visual WM.