Precision of auditory-verbal working memory performance: A behavioral and neuroimaging investigation

This thesis investigated the precision of auditory-verbal working memory (WM) at phonetic, phonological and semantic levels using probe recognition tasks; in these tasks, participants were presented with auditory lists of words or nonwords. After each list, a probe item was presented, and participants were invited to determine whether that item had been in the list. We manipulated the levels of phonetic, phonological or semantic proximity between target and probe items to assess the precision with which items were stored in WM. We showed that phonological WM precision is limited when single-phoneme level resolution is needed, with rejection accuracy strongly declining when target and probe items differ by only one phoneme. We also showed that phonological WM precision declines when multilingual speakers are tested in their less proficient language, suggesting that precision further depends upon the precision of underlying language representations. The fragility of phonological WM traces has furthermore been highlighted in our functional magnetic resonance imaging (fMRI) study, which revealed robust discrimination of phonologically non-overlapping nonwords maintained in WM, but not of phonologically overlapping nonwords. At the phonetic level, we showed that precision for subtle phonetic information tended not to be reliably represented in WM, in line with evidence suggesting that fine-grained phonetic codes are not systematically contained in WM under more naturalistic listening conditions. At the semantic level, we observed high rejection accuracy for probes highly related to target items presented at initial list positions. This suggests that semantic variables influence precision in a time-dependent manner, with early list items being more strongly activated, allowing for optimal discrimination between the target item and a semantically highly related probe item. Hence, while advancing our understanding of the limits and nature of auditory-verbal WM precision, this thesis also highlights the close association of auditory-verbal WM and language domains.