Covaried the number of retroactive tones and the duration of the retroactive interval in 2 experiments with 3 undergraduates using a pitch-recognition memory task. This task was chosen since rehearsal and encoding strategies are minimal in this nonverbal or perceptual memory paradigm. The acquisition process was held constant under the various retroactive interval conditions. Both the retroactive interval duration and the number of tones in the retroactive interval contributed to forgetting. (18 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)