Performance of individuals with left hemisphere stroke and aphasia and individuals with right brain damage on forward and backward digit span tasks

Background: Working memory (WM) limitations have been suggested as a significant source of the linguistic processing deficits observed in individuals with aphasia (IWA). Digits forward (DF) and digits backward (DB) span tasks are frequently used to study WM in both healthy and clinical populations. Unfortunately only a handful of studies have explored digit span in IWA.

Aims: The purpose of the current study is to measure the DF and DB spans of IWA and compare their digit spans to a group with right brain damage, but no aphasia (RBD). Additionally, DF and DB span is compared within each group to determine if there is indeed a performance differential that may support the idea that DB is a more difficult WM task in these populations.

Methods & Procedures: A total of 17 IWA and 14 individuals with RBD participated in a DF and DB span task. Modifications to the span tasks were implemented to accommodate language deficits. A series of two digits were orally presented to each participant continuing to a maximum of eight digits. There were seven trials per digit series. Participants were asked to point to the correct order of digits on a written one- to nine-digit list provided on individual note cards or to verbally repeat the numbers if the participant was able to do so.

Outcomes & Results: IWA demonstrated shorter digit spans than the RBD group. Both groups performed worse on the DB span tasks than the DF span tasks.

Conclusions: The results are consistent with previous studies suggesting that DB span is shorter than DF span in other populations and that there are differences in performance on digit span tasks between the two groups. The differences between RBD group and IWA may be explained by decreased attentional capacity or inefficient resource allocation in IWA, or alternatively, a deficient phonological loop. Future studies should explore these possibilities.