The role of spatial processing in verbal serial order working memory

The serial order system in word production and working memory: A case series approach

Serial order is important in verbal behavior, such as sequencing words in working memory (WM) or arranging phonemes during speech. In both WM and word production, distinct processes are found for item identity and their serial order. In the current study, we investigated whether a shared system supports the serial order of verbal items (phonemes or words) across cognitive functions (WM and production) and tasks (repetition and naming). We recruited 30 participants with chronic stroke-induced aphasia. We examined WM abilities to recall item and serial order information using immediate serial recall tasks of words. We also assessed the ability to accurately sequence phonemes in word repetition and naming tasks, with its impairment indexed by the proportion of misordered phonemes among all incorrect phonemes compared to chance in phonologically related word and nonword responses. We examined how variability of this index of serial order impairment in repetition and naming relates to item and serial order WM capacities. Our findings reveal that serial order WM capacity, but not item WM capacity, was associated with the severity of serial order impairment in repetition, indicating a shared serial order system for WM and repetition. We also found that item WM, but not serial order WM, was associated with serial order impairment in naming, implying an item WM buffer for phonemic sequencing in naming. These results suggest distinct sequencing processes for repetition and naming, each linked to different WM mechanisms. Implications for word production models and the relationship between WM and word production are discussed.

A shared serial order system for verbal working memory and language production: evidence from aphasia

Many aspects of human performance require producing sequences of items in serial order. The current study takes a multiple-case approach to investigate whether the system responsible for serial order is shared across cognitive domains, focusing on working memory (WM) and word production. Serial order performance in three individuals with post-stroke language and verbal WM disorders (hereafter persons with aphasia, PWAs) were assessed using recognition and recall tasks for verbal and visuospatial WM, as well as error analyses in spoken and written production tasks to assess whether there was a tendency to produce the correct phonemes/letters in the wrong order. One PWA exhibited domain-specific serial order deficits in verbal and visuospatial WM. The PWA with verbal serial order WM deficit made more serial order errors than expected by chance in both repetition and writing-to-dictation tasks, whereas the other two PWAs showed no serial order deficits in verbal WM and production tasks. These findings suggest separable serial order systems for verbal and visuospatial WM and a shared system for serial order processing in verbal WM and word production. Implications for the domain-generality of WM, its connection to language production, and serial order processing across cognitive functionssc are discussed.