The “digit span backwards” (DSB) is the most commonly used test in clinical neuropsychology to assess working memory capacity. Yet, it remains unclear how the task is solved cognitively. The present study was conducted to examine the use of visual and verbal cognitive strategies in the DSB. Further, the relationship between the DSB and a complex span task, based on the Simultaneous Storage and Processing task (Oberauer et al., 2003), was investigated. Visualizers performed better than verbalizers in the dual task condition (r _PB = .23) only when the relevant digits were presented optically. Performance in the DSB correlated only weakly with the complex span task in all conditions (all τ ≤ .21). The results indicate that the processing modality is determined by the preference for a cognitive strategy rather than the presentation modality and suggest that the DSB measures different working aspects than commonly used experimental working memory tasks.

The term working memory has been shaped through the work of Baddeley and Hitch (1974) who proposed one of the most influential working memory models in the last century. The concept of working memory describes the temporary storage and manipulation of information, as necessary for complex cognitive tasks like reasoning or language comprehension (Baddeley, 2000). The model includes a visuospatial sketchpad and a phonological loop, responsible for visual and verbal working memory tasks, respectively.

Since working memory is partially defined by its limited capacity (Bireta et al, 2010), several paradigms have been developed to test for inter-individual differences. In clinical neuropsychology, the “digit span backwards” task (DSB) remains the prevalent approach to assess working memory capacity (see Ramsay & Reynolds, 1995). In line with this notion, several psychological test batteries, such as the “Wechsler Adult Intelligence Scales” (WAIS; Wechsler, 2008), include the test in order to assess this facet of cognitive capacity.

In most...