Representing sounds and spellings Phonological decline and compensatory working memory in acquired hearing impairment

Abstract: This thesis examined phonological processing in adults with postlingually acquired moderate-to-severe hearing impairment (HI) and whether explicit working memory processing of phonology and individual working memory capacity (WMC) can compensate for degraded phonological representations in this group (papers I-III). A second aim was to provide reference data for a test of WMC, the reading span test, and to examine the relation between reading span test performance and speech recognition in noise in a larger sample of 50-89 year olds with HI (paper IV). Non-auditory tasks of phonological processing, episodic long-term memory and WMC were used in papers I-III, and both behavioral and electrophysiological measures were collected. Results showed that phonological processing was impaired in the group with HI but that WMC and explicit working memory processing of phonology could be employed to compensate for degraded phonological representations. However, this compensation may come at the cost of interfering with episodic memory encoding. An  electrophysiological marker of HI in text-based rhyme judgments was found. Paper IV presented reference data for reading span test performance in two versions of the test in individuals with HI, and results suggesting that WMC may be differentially predictive of speech recognition in noise in different age groups of older adults with HI. The clinical implications of the present results concerns the double disadvantage of individuals with lower WMC and HI. A structured assessment of WMC in rehabilitative settings would help to identify these individuals and tailor treatment to their needs. The reading span test is suggested as a suitable future candidate for clinical WMC assessment.