On the Role of Inhibition in Suppression-Induced Forgetting

Suppressing retrieval of unwanted memories can cause forgetting, an outcome often attributed to the recruitment of inhibitory control. This suppression-induced forgetting (SIF) generalizes to different cues used to test the suppressed content (cue-independence), a property taken as consistent with inhibition. But does cue-independent forgetting necessarily imply that a memory has been inhibited? Tomlinson et al. (2009) reported a surprising finding that pressing a button also led to cue-independent forgetting, which was taken as support for an alternative interference account. Here we investigated the role of inhibition in forgetting due to retrieval suppression and pressing buttons. We modified Tomlinson et al.’s procedure to examine an unusual feature they introduced that may have caused memory inhibition effects in their experiment: the omission of explicit task-cues. When tasks were uncued, we replicated the button-press forgetting effect; but when cued, pressing buttons caused no forgetting. Moreover, button-press forgetting partially reflects output-interference effects at test and not a lasting effect of interference. In contrast, SIF occurred regardless of these procedural changes. Collectively, these findings indicate that simply pressing a button does not induce forgetting, on its own, without confounding factors that introduce inhibition into the task and that inhibition likely underlies SIF.

Serial recall

Serial memory refers to the ability to recall a novel sequence of items or events in the correct order. In the laboratory, the dominant tool used to assess this mental faculty is the immediate serial recall (hereafter, ‘serial recall’) task in which participants are given a sequence of typically verbal, visual, or spatial items that they must subsequently recall in their original presentation order. Serial recall is a deceptively simple task—the apparent ease with which people accomplish it masks the wealth and complexity of findings this task has generated, and the computational theories that have been developed to account for them. In this chapter, I review benchmark findings of serial recall that have been observed across the verbal, visual, and spatial short-term memory domains, and I interpret them with reference to the core mechanisms embodied in contemporary computational theories of serial recall. This analysis identifies four mechanisms that are common to the three content domains—namely, position marking, a primacy gradient, competitive queuing, and response suppression. Additionally, evidence suggests that in verbal serial recall both the encoding and retrieval of items is sensitive to item similarity—similarity-sensitive encoding and retrieval—and that item retrieval is accompanied by output interference. By contrast, in visual and spatial serial recall there is evidence for similarity-sensitive retrieval, but the relevant empirical observations that evince similarity-sensitive encoding and output interference are yet to be studied in the visual and spatial domains. I conclude by outlining some challenges for future research.

Testing a Strategy-Disruption Account of the List-Strength Effect

Presenting items multiple times on a study list increases their memorability, a process known as item strengthening. The list-strength effect (LSE) refers to the finding that, compared to unstrengthened (pure) lists, lists for which a subset of the items have been strengthened produce enhanced memory for the strengthened items and depressed memory for the unstrengthened items. Although the LSE is found in free recall ( Tulving & Hastie, 1972 ), it does not occur in recognition ( Ratcliff et al., 1990 ). In free recall, the LSE in mixed lists is attributed to a sampling bias promoting priority recall of strong items and consequent output interference affecting weak items. We suggest that, in recognition, the disruption of this pattern through the randomization of test probes is responsible for the null LSE. We present several pilot experiments consistent with this account; however, the registered experiment, which had more statistical power, did not support this account.

Selective directed forgetting: Eliminating output order and demand characteristics explanations

Previous research has shown that giving an instruction to forget part of a studied list of items impairs the subsequent retrieval of these items compared with those not cued to be forgotten. This selective directed forgetting (SDF) effect has been found with slightly different procedures and in adolescents and young adults. While recent research has suggested that executive control might underlie SDF, alternative explanations that rely on procedural issues still have not been investigated. Specifically, SDF might essentially reflect output interference from the items cued to be remembered, so that the earlier recalled items interfere with the later recalled items. The effect could also result from demand characteristics: Participants might withhold the to-be-forgotten items to comply with the experimenter’s implicit goals or might not be willing to engage in the effort of retrieving all studied information. The results from two experiments showed that (1) the to-be-forgotten items were less accessible and were not influenced by output interference from to-be-remembered items (Experiment 1), and (2) SDF was still present when participants were offered monetary reward for retrieving as many items as possible (Experiment 2). Hence, the findings do not provide support to explanations of SDF based on output interference and demand characteristics.

Release from output interference in recognition memory: A test of the attention hypothesis

Retrieval results in both costs and benefits to episodic memory. Output interference (OI) refers to the finding that episodic memory accuracy decreases with increasing test trials. Release from OI is the restoration of original accuracy at some point during the test. For example, a release from OI in recognition memory testing occurs when the semantic similarity between stimuli decreases midway through testing, suggesting that item representations stored on early trials cause interference on tests occurring on later trials to the extent that the earlier items share features with the latter items. In two recognition memory experiments, we demonstrate release from OI for words and faces. We also test whether release from OI is the result of interference or is due to a boost in attention caused by reorienting to a novel stimulus type. A test for the foils presented during the initial test list supports the interference account of OI. Implications for models of memory are discussed.