This study is the fourth in a series of studies that have attempted to examine the relationship between two separate aptitude factors--associative memory and reasoning--to various performance criteria in a hierarchical learning task utilizing computer-assisted instruction. Two clear effects seem to emerge from the data. During learning, the availability of past examples reduces the load on memory, thus facilitating performance for subjects low on memory ability. Also, subjects with high reasoning ability benefit substantially from more complex examples and seem to be able to utilize availability better than subjects of lower reasoning ability. Since these explanations of complexity effects and all observations on posttest performance are based primarily on post-hoc reasoning, further studies are recommended to confirm them. (Author/MF)