May, C. P., Hasher, L., & Kane, M. J. (1999). The role of interference in memory span. Memory & Cognition, 27, 759-767.
Various memory span measures are widely used to determine individual and group differences in the capacity available to manage cognitive demands. We investigated the possibility that memory span measures do not provide pure indices of mental capacity, but rather that they also reflect susceptibility to proactive interference (PI). We tested younger and older adults on two different span measures, and manipulated testing procedures to reduce PI for these tasks. For older adults, span estimates improved reliably with each PI-reducing manipulation; for younger adults, scores increased when multiple PI manipulations were combined, or when within-task PI was especially high. The findings suggest that susceptibility to PI critically influences span performance, and raise the possibility that interference-proneness is a primary determinant in cognitive behaviors previously thought to be governed by capacity.
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