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The effects of pre- and post-stimulus cues on detection were studied using 2-alternative forced-choice tasks. The stimuli used were tones presented to Ss through earphones and dots presented on TV monitors. The tones varied in pitch and intensity and the dots varied in displacement both horizontally and vertically. Thus Ss could be required to make discrimination in 4 dimensions. Performance on 1-dimensional input—1-dimensional output was superior to that for 4-dimensional input—1-dimensional output even when the stimulus for which a response was required was cued 4.0 sec. before its presentation. The duration of the post-stimulus cue delay, 0.10 sec. to 4.0 sec., had no differential effect on performance levels. These results are quite different from those reported for absolute judgment tasks.