Representation of serial order in humans: a comparison to the findings with monkeys (Cebus apella).

In a number of studies, serially organized behavior in humans has been examined using a procedure developed for use with pigeons and monkeys. There have been few direct comparisons, however, between the data collected with humans and that collected with nonhumans, and none with respect to the interesting latency effects noted with nonhumans. The purpose of this experiment was to make this comparison. Human subjects were trained to respond to five simultaneously presented stimuli (A, B, C, D, and E) in a specific order (A-->B-->C-->D-->E) and were then tested with all 10 pairwise combinations of the five stimuli, followed by all 10 triplet combinations of the five stimuli. Mirroring the findings with monkeys (Cebus apella), humans showed a first-item effect, a missing-item effect, and a symbolic-distance effect. These results suggest that during the course of learning the five-item serial-order task humans form an internal representation of the series and access that representation to guide their behavior.