It is predicted that humans have a preferred amount of stimulus variation in their perceptual environment. This hypothesis was tested by obtaining S's pleasantness ratings of sequences of tones which sounded like simple music and presented increasing amounts of stimulus variation. Increasing the stimulus variation was accomplished by increasing the variance and the information in the elements making up the sequences. The mean pleasantness ratings, as predicted, increased up to a moderate amount of stimulus variation and then declined. A secondary hypothesis predicted that Ss with much training and interest in music would rate the tone sequences with larger amounts of stimulus variation as more pleasant than would Ss with little training and interest in music. The results also supported this hypothesis. (PsycINFO Database Record (c) 2006 APA, all rights reserved)