Two systems theory posits a ventral stream for object processing and a dorsal stream for spatial processing. Does this division of labor have consequences for working memory (WM)? We examined WM for object and spatial properties. In different blocks, the two relevant properties were from one stream or from both. Depending on assumptions, different two-systems predictions can be made. One prediction is that elements within one stream are encoded or output easier than elements from different streams. An alternative to two-systems theory is the hypothesis that elements are encoded independently and only the difficulty of elements matters.

We used a VWM task with displays of four items varying on both object and spatial properties (object: pattern, shape identity; spatial: orientation, location). In the two within-system blocks, participants reported the two object or two spatial properties. In each of the four between-system blocks, one property from each system was reported (e.g., pattern and location). In Experiment 1, a symbolic response was required (letters corresponding to properties). In Experiment 2, a more analog action response was required (shorthand drawings). In each experiment, there were reliable differences in the ease of reporting particular properties (p's<.001). However, there were no effects of grouping -- mean trial recall was 1.89 properties for within-system blocks and 1.90 for between-system blocks (F<1; the within-subject Standard Error of 0.01 indicates high experimental sensitivity). Thus, difficulty of independent properties drove performance, not two-systems architecture.