Serial list linking by macaque monkeys (Macaca mulatta): list property limitations.

Four sophisticated macaque monkeys (Macaca mulatta) learned 6 different, 15-item ordinal lists (via conditional, 2-choice discriminations) as part of a study assessing some properties of serial list memory in monkeys. After assuring that the first 3 lists were well retained, the researchers attempted to link these by training only the 2 end-item pairs that ordered all 45 items into an inclusive series. A 20-day test of possible pairings among these 45 items was then conducted. Subsequently, the other 3 lists were trained and tested for retention, but no link training was provided. Then, a test like the one that had followed linking was administered. Unlike previous outcomes with three 5-item lists, linking did not yield immediate merger of three 15-item lists into a 45-item list, although 45-item lists were acquired after sufficient exposure to the testing/training regimen under both linking and nonlinking conditions. List length as a limiting factor in linking suggested processing restrictions analogous to those observed in human list memory. Results supported further investigation of list-linking characteristics.