Forgetting is a Feature, not a Bug: Intentionally Forgetting Some Things Helps Us Remember Others by Freeing up Working Memory Resources

We used an item-method directed forgetting paradigm to test whether instructions to forget or to remember one item in a list affects memory for the subsequent item in that list. In two experiments, we found that free and cued recall were higher when a word-pair was preceded during study by a to-be-forgotten (TBF) word pair. This effect was cumulative – performance was higher when more of the preceding items during study were TBF. It also interacted with lag between study items – the effect decreased as the lag between the current and a prior item increased. Experiment 2 used a dual-task paradigm in which we suppressed either verbal rehearsal or attentional refreshing during encoding. We found that neither task removed the effect, thus the advantage from previous TBF items could not be due to rehearsal or attentional borrowing. We propose that storing items in long-term memory depletes a limited pool of resources that recovers over time, and that TBF items deplete fewer resources, leaving more available for storing subsequent items. A computational model implementing the theory provided excellent fits to the data.

Comparison of figural intrusion errors in three amnesic subgroups

To examine the contribution of memory deficits and executive dysfunction to the production of prior-item intrusion errors, Korsakoff, mesial temporal amnesic, and anterior communicating artery aneurysm (ACoA) patients’ performance on the Visual Reproduction subtest of the Wechsler Memory Scale-Revised (WMS-R) was assessed. The Korsakoff patients were matched to the mesial temporal group in terms of severity of amnesia, while the ACoA group, which was less severely amnesic, was matched to the Korsakoff group in their performance on executive tests. Results indicated that at immediate recall, Korsakoff patients made significantly more intrusions than mesial temporal and ACoA patients. Conversely, after a delay, ACoA patients tended to make more intrusions than the other groups. Findings suggest that intrusions are due to a combination of deficient memory and executive dysfunction. A further comparison of a subgroup of ACoA patients matched to the Korsakoff patients in terms of severity of amnesia, however, revealed differences in the pattern of intrusions of these two groups, suggesting that different mechanisms may underlie Korsakoff and ACoA patients’ susceptibility to interference. (JINS, 1995, 1, 561–567.)

Proactive Interference in Short-Term Memory: Recall Probability as a Function of Prior Item Recall

In two different experiments, one with 23 brain surgery patients and one with 39 college students, proactive interference in short-term memory was evaluated as a function of the recall of the just preceding item in a Brown-Peterson distractor technique. In the first experiment, the probability of an error following an error was .25, and the probability of an error following a correct item was .24. In the second experiment, there was also no significant effect ( p > .05) of either prior item repetition or recall upon recall of the subsequent item, except in the case of prior items having a retention interval of 24 sec. In that case, well-remembered items exerted less proactive interference than items on which an error had been made. The results were evaluated in terms of a theory derived from the selector mechanism proposed for long-term memory (Postman, Stark, & Fraser, 1968).

Effect of Instruction on Recall of Movements

A 4 × 4 factorial design with repeated measures across retention intervals and instructions was employed to determine the effect of instruction on recall ability of movement information from short-term motor memory. Each of the 16 Ss received all 16 possible treatment combinations. While both retention interval and instruction showed significant effects, there was no significant interaction. The reverse-order instruction was affected by the length of the retention interval while the no-prior-item, last-distance, and drop instructions were uninfluenced. No evidence supported the trace-decay hypothesis of forgetting. Ss seem easily able to remove information from memory or ignore information input so it is not represented in memory.

Proactive Interference in Short-Term Memory as a Function of Prior-Item Retention Interval

The experiment was conducted to examine the effect of prior-item retention interval on the retention of a given item in a short-term memory test series. There were five conditions. The retention interval for the fifth test of five successive tests was 15 sec. for all five conditions. The retention intervals for tests 1–4 were constant for a condition but varied across conditions. These retention intervals were 5, 10, 15, 20 and 25 sec. Five consonant trigrams constructed from the set of letters sharing the vowel sound “e” were used for all conditions. Recall on test 5 was a direct function of prior-item retention interval. The data indicate, therefore, that the availability of prior items for proactive interference is an inverse function of prior-item retention interval.