Two experiments involving memory retrieval of auditorilv and visuallv presented materials were performed. In Experiment I, subjects were presented with memory sets of 1, 2, or 4 stimuli and then with a test item to be classified as belonging or not belonging to the memory set. In Condition 1, each memory stimulus was a single, auditorily presented letter. In Condition 2, each memory stimulus was a visually presented letter. In Conditions 3 and 4, each memory stimulus was a pair of letters, one presented visually and the other auditorily. Mean reaction time (RT) for the classification task increased as a function of number of memory stimuli at equal rates for all four conditions. This was interpreted as evidence for a parallel scanning process in Conditions 3 and 4 where the auditory item and visual item of each memory stimulus pair can be scanned simultaneously. Experiment II compared memory retrieval for a simultaneous condition in which auditory and visual memory items were presented as pairs with a sequential condition in which mixed auditory-visual memory sets were presented one item at a time. RTs were shorter for the simultaneous condition. This was interpreted as evidence that parallel scanning may depend upon memory input parameters.These two studies investigate the problem of how people retrieve information from memory. In particular, they are concerned with whether people are able to retrieve information about two or more different sets of memory information at the same time. If such simultaneous retrieval is possible, then an assumption of parallel processing can be built into models of the retrieval process, making possible theories of considerable power.Experiment I was an attempt to demonstrate simultaneous retrieval of auditorily and visually presented information from short-term memory.Sternberg (1966, 1969) has argued that retrieval from short-term memory involves a serial scan of the items in memory. He based this argument on the results of a series of experiments in which subjects were required to decide whether or not a test item was included in a short list of previously memorized items. Typically, the reaction time (RT) for the required two-choice response is a linearly increasing function of the number of items in the memory set. Each additional memory item seems to add a constant to the time required for the decision. This suggests that, before a decision is made, subject compares the test item with each memory item. Each comparison requires (on the average) one unit of time. The linearly increasing function reflects the increasing number of comparisons required when additional memory items are involved. The slope of the function is a measure of the rate of retrieval.If large amounts of memory information are involved in a retrieval situation, a simple serial scan would be inefficient. Any general theory of how humans retrieve information from their memories must almost certainly involve processes more complex than simple serial scans.