Switching between memory and perception: moving attention or memory retrieval?

Weber, Burt, and Noll (1986) estimated that the time needed to switch attention between memory and perception was around 300 msec. The first two experiments in the present paper estimated switching time using a variation of their task. Subjects reported aloud lists of six items. The items were read off a computer screen (perception), recited from memory, or reported alternately from the two sources. The data show that the switching-time estimate is influenced by input/output compatibility, response-initiation times, and memory load. When these factors were controlled, estimated switching time dropped to around 100-150 msec. The data suggest, however, that the switch from perception to memory might be slower than the switch from memory to perception, which would invalidate the formula used to compute switching time. Experiment 3 tested the time for a single switch from perception to memory and a single switch from memory to perception by restricting report to one pair of items in the list. When the to-be-reported pair was precued, estimated switching time dropped to zero. When the pair was not precued, the memory-to-perception switching time remained at zero, but the perception-to-memory time was more than 400 msec. The pattern of results forced a reconceptualization of the task in terms of memory retrieval rather than attention switching. The attention-switching times appear to reflect processes required to select items from memory.