Drawings reveal changes in object memory, but not spatial memory, across time.

Time has an immense influence on our memory. Truncated encoding leads to memory for only the 'gist' of an image, and long delays before recall result in generalized memories with few details. Here, we used crowdsourced scoring of hundreds of drawings made from memory after variable encoding (Experiment 1) and retentions of that memory (Experiment 2) to quantify what features of memory content change across time. We found that whereas some features of memory are highly dependent on time, such as the proportion of objects recalled from a scene and false recall for objects not in the original image, spatial memory was highly accurate and relatively independent of time. We also found that we could predict which objects were recalled across time based on the location, meaning, and saliency of the objects. The differential impact of time on object and spatial memory supports a separation of these memory systems.

Tracking induced forgetting across both strong and weak memory representations to test competing theories of forgetting.

Here we employ a novel analysis to address the question: what causes induced forgetting of pictures? We use baseline memorability as a measure of initial memory strength to ask whether induced forgetting is due to (1) recognition practice damaging the association between the memory representation and the category cue used to activate the representation, (2) the updating of a memory trace by incorporating information about a memory probe presented during recognition practice to the stored trace, (3) inhibitory mechanisms used to resolve the conflict created when correctly selecting the practiced item activates competing exemplars, (4) a global matching model in which repeating some items will hurt memory for other items, or (5) falling into the zone of destruction, where a moderate amount of activation leads to the highest degree of forgetting. None of the accounts of forgetting tested here can comprehensively account for both the novel analyses reported here and previous data using the induced forgetting paradigm. We discuss aspects of forgetting theories that are consistent with the novel analyses and existing data, a potential solution for existing models, proposals for future directions, and considerations when incorporating memorability into models of memory.

Induced forgetting of pictures across shifts in context.

Previous research from our lab has shown that recognizing an object stored in visual long-term memory leads to the forgetting of related objects. Here we ask whether context, an integral aspect to modern models of memory, plays a role in induced forgetting. We manipulated the activated context at test, both externally (e.g., changes in testing room) and internally (e.g., 1 hr and 24 hr later). We found that only interfering with the ability to internally reinstate context after 24 hr eliminated induced forgetting. Thus, we demonstrate that mental context reinstatement plays a role in induced forgetting and specify that models of memory should incorporate internal context reinstatement as an underlying factor of forgetting. We also propose a process model of induced forgetting, discuss limitations of laboratory-based memory tasks, and offer a new term, induced suppression, to collectively describe this robust phenomenon. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Induced Forgetting Is the Result of True Forgetting, Not Shifts in Decision-making Thresholds.

Induced forgetting occurs when accessing an item in memory appears to harm memory representations of categorically related items. However, it is possible that the actual memory representations are unharmed. Instead, people may just change how they make decisions. Specifically, signal detection theory suggests this apparent forgetting may be due to participants shifting their decision criterion. Here, we used behavioral and electrophysiological measures to determine whether induced forgetting is truly due to changes in how items are represented or simply due to a shifting criterion. Participants' behavior and brain activity showed that induced forgetting was due to changes in the strength of the underlying representations, weighing against a criterion shift explanation of induced forgetting.

Medium strength visual long-term memories are the most fragile.

What memories do humans forget? One theory proposes that memories stored with moderate activation levels are weakened when faced with competitive stress so that they are particularly prone to be forgotten. However, research suggests that visual long-term memories are stronger than memories of other modalities, and therefore may never fall into this moderate activation zone. Here we tested these competing predictions by showing to-be-remembered pictures while we recorded event-related potentials (ERPs) indexing memory activation during encoding. We found that visual memories with medium levels of activation when first encoded were more prone to forgetting than memories with high or low encoding activation levels, but this only occurred if a memory was faced with competition. This study shows that we forget moderately activated memories when they are subjected to competition, regardless of the modality of experience.

Stimulus-induced Alpha Suppression Tracks the Difficulty of Attentional Selection, Not Visual Working Memory Storage.

Human alpha-band activity (8-12 Hz) has been proposed to index a variety of mechanisms during visual processing. Here, we distinguished between an account in which alpha suppression indexes selective attention versus an account in which it indexes subsequent working memory storage. We manipulated two aspects of the visual stimuli that perceptual attention is believed to mitigate before working memory storage: the potential interference from distractors and the size of the focus of attention. We found that the magnitude of alpha-band suppression tracked both of these aspects of the visual arrays. Thus, alpha-band activity after stimulus onset is clearly related to how the visual system deploys perceptual attention and appears to be distinct from mechanisms that store target representations in working memory.

Unintentional forgetting is beyond cognitive control.

Intentional forgetting refers to the attempt to marshal top-down control to purposefully forget, and has been demonstrated in the laboratory using directed forgetting paradigms. Here, we asked whether the mechanisms of top-down control can run in the opposite direction to prevent the forgetting of information; that is, can we actively resist unintentional forgetting? Recognition-induced forgetting is an unintentional forgetting effect in which accessing one memory leads to the forgetting of related memories. Just as intentional forgetting possesses intuitively appealing control over eliminating undesirable memories, resisting unintentional forgetting over desired memories would improve cognitive performance. We showed subjects a 9-min video to teach them about the recognition-induced forgetting paradigm and how recognition of certain objects unintentionally leads to forgetting of semantically related objects. After testing their comprehension of the video, we conducted a typical recognition-induced forgetting experiment and challenged the subjects to resist this form of unintentional forgetting. Despite their knowledge of the forgetting effect, and the challenge to subjects to resist the forgetting induced by the paradigm, recognition-induced forgetting persisted. These results show that knowledge of this unintentional forgetting phenomenon and the challenge to resist forgetting do not eliminate it, suggesting that it is cognitively impenetrable.

Modality-specific forgetting.

A large body of literature agrees that accessing a target memory appears to trigger a difference-of-Gaussian memory activation pulse under which the target representation is activated and categorically flanking items are suppressed and forgotten. The nature of the underlying forgetting mechanism is far from settled, with support for several theories of forgetting. Here we argue the debate is partly fueled by different forgetting mechanisms underlying the forgetting of different memoranda. We capitalized on the unique aspect of the recognition-induced forgetting paradigm to test forgetting of both pictures and words in identical recognition-practice and restudy tasks. We found that memory for pictures and words followed different patterns of forgetting. Specifically, forgetting was retrieval specific for words, in that forgetting occurred only when words were recognized, and not when words were merely restudied. However, forgetting was not retrieval specific for pictures, in that forgetting occurred both when pictures were recognized as well as restudied. Further, patterns of forgetting operated along different category-level groupings for pictures and words. Words grouped along the superordinate level were susceptible to forgetting but pictures were not. The strength of this design is the ability to directly compare forgetting for different memoranda, establishing that patterns of forgetting are modality specific. These findings demonstrate that the mechanisms underlying forgetting may differ as a function of the particular memoranda, emphasizing the need for examining forgetting in long-term memory across modalities.