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Six experiments are presented that examined the constraints underlying performance in two visuo-spatial span tasks. In the Location Span Test (LST), participants have to memorize the cells of a 5×5 matrix containing arrows, while in the Direction Span Test (DST) they have to memorize the cells pointed at by arrows. The main objective was to assess whether both tasks were similarly influenced by experimental factors. Results showed that performance improved with longer encoding time (1-s. vs. 3-s) only for the DST. Maintenance interval (0-s vs. 5-s) and order of item difficulty (ascending vs. descending) have no effect either on the LST or on the DST. Another experiment indicated that the DST is a better predictor of fluid intelligence. These results seem to provide evidence that the LST and the DST relate to different constructs. Implications of these findings for the distinction between short-term and working memory span tasks are discussed.