Pupil dilations following pairs of identical and related to-be-remembered words

Two experiments are reported in which the spacing between pairs of identical (Experiment 1) or pairs of related (Experiment 2) to-be-remembered words were varied while pupil diameter and frequency judgments were measured. In Experiment 1, frequency judgments increased with increases in spacing length. In Experiment 2, frequency judgments decreased with increases in spacing length. In both experiments, however, pupil dilations increased with increases in spacing length. These results are interpreted as supporting theories that argue that massed repetitions require less processing than spaced repetitions. It is argued that this deficiency in processing reduces retention of massed repetitions of identical words. For massed presentation of related words, organizational strategies can be used with little effort to increase retention.