Figure 9. Latency of response to first and second items of subsets.  The top panel shows the mean latency of responding (in seconds) to the first item of two-item test pairs as a function of that item's position on the original list (ABCDE).  The bottom panel shows the mean latency of responding to the second item of two-item subset pairs as a function of the number of items that intervened between those items on the original list.  Filled squares show data from monkeys (D'Amato and Colombo, 1988); open circles are data from pigeons (Terrace, 1987).