Using both an auditory and a visual short-term store to increase digit span

Can digit span be increased by storing digits nonredundantly in both an auditory short-term store and a visual short-term store (dual storage)? In Experiment 1, when four digits were presented visually and then the remaining digits were presented auditorily, digit span increased three digits over a baseline measurement, but only when the auditorily presented digits were reported first (inverted response). Normal order of response for this presentation was not as effective. Possible reasons for the advantage of inverted response are suggested, based upon dual storage. For all-auditory and all-visual presentations that controlled for parsing, digit span increased only 1 to 1.5 digits over baseline, and inverted and normal order of response did not differ. Experiment 2 demonstrated that an improvement for dual storage could occur when the type of presentation was held constant and the order of response was normal rather than inverted. The results are consistent with the idea of separate auditory and visual short-term stores.