The properties of retention intervals and their affect on retaining prospective memories

Five experiments were conducted to explore how the character of the retention interval affected event-based prospective memory. According to the canons of retrospective memory, prospective per-formance should have been worse with increasing delays between intention formation and the time it was appropriate to complete an action. That result did not occur. Rather, prospective memory was better with increasing retention intervals in Experiments 1 A, IB, and 3. In manipulating the nature of the retention interval, the authors found that there were independent contributions of retention interval length and the number of intervening activities, with more activities leading to better prospective memory (Experi-ments 2 and 3). The identical retention intervals did not improve retrospective memory in Experiment 4. Theoretical explanations for these dissociations between prospective and retrospective memory are considered. In the classic studies performed by Hermann Ebbinghaus (1885/ 1964), he demonstrated that memory declines with increasing delays between study and test. By teaching himself lists of 13 syllables to a criterion of two correct recalls, he systematically varied the retention interval from 20 min to 31 days. Ebbinghaus discovered that the forgetting curve, as it is now known, was approximated by a logarithmic function with a fast initial rate of forgetting over the near term and a slower decline in forgetting as retention intervals were increased. The forgetting curve appears to be a very general property of retrospective memory because it is true of foreign language learning (Bahrick & Phelps, 1987), typing skills (Baddeley & Longman, 1978) and even cardiopulmonary resuscitation skills (McKenna & Glendon, 1985). Although there is no agreement on why this law of forgetting is so pervasive across different materials, many memory theorists favor interfer-ence accounts of retrospective forgetting over decay theories that depict memory traces as simply crumbling into parts over tim