Gave 3 male capuchin monkeys a visual delayed matching-to-sample task. Delay intervals spent in moderate ambient illumination, as opposed to darkness, resulted in sharp performance decrements. However, neither white noise nor recorded monkey vocalizations interfered with delayed matching performance, despite evidence that the Ss attended to the vocalization stimuli. There was some indication that vocalization during the delay interval reduced the interference caused by illumination. This result is interpreted in terms of attentional mechanisms. (PsycINFO Database Record (c) 2006 APA, all rights reserved)