The purpose of these studies was to provide evidence to support either the dual-coding hypothesis or the single-system hypothesis of human memory. In one experiment, college subjects were shown a mixed series of words and pictures either while simultaneously engaged in shadowing (repeating aloud) a prose passage presented via earphones or while free of such distractions. On a multiple-choice recognition test, it was found that the verbal shadowing task interfered with word performance but failed to affect pictorial recognition memory, indicating that verbal information and pictorial information may be processed independently in parallel recognition memory systems. In a similar experiment recall rather than recognition was the dependent measure. While the usual pictorial superiority was found, the verbal shadowing task interfered with picture as well as word retention, suggesting that in memory tasks where verbal reports are required, subjects characteristically attempt to translate easily labelable pictorial information into verbal terms during the encoding phase. Thus there does appear to be a separate visual iconic memory system, but it normally operates in total independence of the verbal system only when the anticipated use of information is nonverbal in character. (Author/WR)