Absence of a redundant-signals effect in a reaction time task with divided attention

In letter-identification reaction time experiments, a redundant-signals advantage was obtained when one location contained an irrelevant letter on single-target trials. It was not obtained when the position was blank. This confirms a prediction from a previous analysis in terms of variable criterion theory. The intercept of the linear function relating the growth of excitatory strength for redundant targets to that for the sum of single-target strengths is determined by the presence or absence of an irrelevant distractor. This confirms a second prediction. In this task, the redundant-signals advantage is due to distraction from an irrelevant stimulus occupying a relevant location. There is also evidence for a smaller distraction effect even from a redundant target. These findings are inconsistent with predictions of separate activation theory. Apparent differences be-tween these results and those of tachistoscopic recognition experiments are discussed.