Working memory capacity is differentiated theoretically along two dimension
s: contents and functions. The resulting 3 x 3 matrix was operationalized b
y 23 tasks sampled from the literature. Data for these tasks from 128 parti
cipants were analyzed by exploratory and confirmatory factor analysis. Rega
rding the content facet, spatial working memory was clearly distinct from t
he other two content categories. A distinction between verbal and numerical
working memory was not warranted. On the functional dimension the postulat
ed categories of simultaneous storage and transformation and of coordinatio
n could not be separated, The third category was clearly separate from the
first two functions. This factor could be interpreted to reflect a mixture
of variance due to mental speed and to supervisory functions of the central
executive. (C) 2000 Elsevier Science Ltd. All rights reserved.