Taxonomy

Memory Mechanisms Taxonomy

29 constructs of human memory, each empirically established in humans and implementable in current AI memory architectures, grouped by the purpose each one serves.

The structure

Select a group to open the level beneath it; a mechanism opens its own page.

01

How were memory constructs selected?

Inclusion Criteria

Using ⁠Tulving's (1972)⁠ episodic/semantic distinction and ⁠Squire's (2004)⁠ declarative/non-declarative taxonomy as a starting point, the memory literature on systems and processes was surveyed and each candidate was analyzed against two criteria.

  1. 01

    Empirically established in humans, evidenced by a stable definition with agreed-upon examples, an identified neural substrate or lesion dissociation, and quantitative or meta-analytic effect sizes.

  2. 02

    Implementable and measurable in current AI memory architectures, whether or not it has yet been measured.

How the candidates sorted against the two criteria is shown on the Method page.

02

What was included and excluded?

Included Constructs

29 constructs were identified across the human memory literature meeting both criteria above.

Constructs were grouped by what kind of purpose each one is serving rather than by the declarative and non-declarative division.

Memory Systems
8 Memory Systems Retains ⁠Squire's (2004)⁠ organization by kind of representation.
Representational Structures
4 Representational Structures Organizing schemes imposed over stored content.
Memory Processes
12 Memory Processes Operations performed on stored content.
Metacognition
5 Metacognition Second-order judgments about stored content.

Excluded Constructs

Examples of candidates that were considered and excluded, either for failing one of the two criteria or for being the wrong unit of comparison. They are listed because their exclusion reflects the boundaries of the criteria rather than the limits of the review.

Sensory Memory Fails criterion 2

Sensory memory meets the first criterion, with an established paradigm (⁠Sperling, 1960⁠), documented decay parameters, and reported effect sizes, but fails the second. Its counterpart in an AI system is input tokenization, which is not memory in any sense examined here. The exclusion is noted explicitly because existing surveys of AI memory routinely include sensory memory as a fifth system, on the strength of that mapping.

Encoding Wrong unit: a stage, not a function

Encoding was excluded as a processing stage rather than a function. Stages describe when an operation occurs rather than what it accomplishes, which makes them the wrong unit for comparison across substrates. Encoding specificity is treated instead as a cross-cutting factor.

Transactive Memory Wrong unit: a group, not a person

Transactive memory was excluded as a different unit of analysis rather than a different construct. Wegner's account describes encoding, storage, and retrieval distributed across members of a group, with individuals holding a directory of who knows what (⁠Wegner et al., 1991⁠). Because the system is the group rather than the person, it carries no neural substrate of the kind the first criterion requires, and it is not a factor modulating individual memory processes in the way the cross-cutting factors are.

It is retained as a framing device for the use-case comparison, where the relevant question is not what memory functions an AI system should have but what a transactive partner requires in order to be a good one.

03

Cross-Cutting Factors

Cross-Cutting Factors

A third category holds influences that shape multiple memory constructs without being constructs themselves.

They are not functions the memory system performs but conditions under which it performs them. A factor was included where it meets all three of the following:

  1. 01

    It has documented effects on two or more of the constructs.

  2. 02

    It carries quantitative or meta-analytic evidence for those effects.

  3. 03

    It raises a question about AI memory that the construct-level analysis cannot address.

Some factors have a well-localized neural substrate, as emotional modulation does in the basolateral amygdala (⁠McGaugh, 2004⁠); others, such as cultural variability, have none. What distinguishes a factor from a construct here is not anatomy but scope: a factor conditions how multiple constructs operate rather than being an operation itself.

Examples

Cultural Variability

Human memory is shaped by culture, which influences the age of earliest recollection and the content and style of autobiographical memories (⁠Wang, 2001⁠), is transmitted developmentally through the ways caregivers reminisce with children about the past (⁠Nelson & Fivush, 2004⁠), and appears to moderate whether detailed episodic recall supports or undermines well-being (⁠Wang et al., 2018⁠; see ⁠Wang, 2021⁠, for review). Cultural variation is not a property of one memory mechanism but a factor operating across them, from perceptual encoding through autobiographical narrative.

The AI question it raises

Large language models are trained on text scraped from the web, which overrepresents dominant voices rather than representative ones: GPT-2 was trained on web pages linked from Reddit, whose US users are 67% male and 64% aged 18 to 29, and only 8.8 to 15% of Wikipedia editors are women (⁠Bender et al., 2021⁠). Filtering compounds the skew rather than correcting it, since blocklist-based cleaning removes 42% of documents in African American English and 32% in Hispanic-aligned English, against 6.2% of White-aligned English, leaving 97.8% of the resulting corpus in the latter (⁠Dodge et al., 2021⁠). What is absorbed is not a separable contaminant but the meaning of the language itself: word embeddings trained on ordinary web text reproduce the full range of human associations, from the morally neutral to the prejudicial, at effect sizes matching those measured in people (⁠Caliskan et al., 2017⁠). The consequences are measurable in current systems. Models produce outputs resembling the cultural values of English-speaking and Protestant European countries when prompted without a specified cultural identity (⁠Tao et al., 2024⁠); their expressed opinions diverge from those of the US public by roughly the margin separating Democrats and Republicans on climate change, with older, widowed, and religiously observant respondents least well represented (⁠Santurkar et al., 2023⁠); and they hold covert stereotypes about speakers of African American English more negative than any human stereotypes about African Americans ever experimentally recorded (⁠Hofmann et al., 2024⁠).

Emotional Modulation

Emotional arousal modulates how strongly an event is retained, acting on storage systems already in use rather than through a separate emotional memory store (⁠McGaugh, 2004⁠). The mechanism is contested: on an alternative account the amygdala binds items to emotional responses, and those bindings are simply forgotten more slowly than the item-context bindings the hippocampus supports (⁠Yonelinas & Ritchey, 2015⁠). The effect is selective rather than uniform, but the selection is by priority rather than spatial position: arousal amplifies whatever already dominates the competition for processing and suppresses what does not, producing a winner-take-more pattern in both perception and consolidation (⁠Mather & Sutherland, 2011⁠). Because arousal acts at encoding and after it (⁠McGaugh, 2004⁠), and acute stress separately impairs retrieval, more so for emotional than neutral material (⁠Shields et al., 2017⁠), it cuts across four rows rather than sitting in one. Retrieval is also a starting point and not only an end point, since recalling an emotional event reshapes the trace available to later recall (⁠Kensinger & Ford, 2020⁠), which is consistent with ⁠Squire's (2004)⁠ treatment of arousal modulation as affecting both declarative and non-declarative memory. Clinically, the same modulation is implicated in the involuntary character of trauma memory (⁠Brewin, 2014⁠).

The AI question it raises

AI memory systems have no analogue to arousal modulation. When a system stores something a user has said, it later finds that material by how closely a numerical representation of the current question matches those of what was stored, a similarity calculation with no reference to how the material was acquired. Agent architectures add two adjustments to this: a recency weight that fades with time, and an importance rating from 1 to 10 that a language model assigns at the moment of storage by being asked how significant the item seems (⁠Park et al., 2023⁠). That rating is the closest counterpart to emotional arousal, and it does more than order search results, since accumulated importance also determines when the system pauses to draw higher-level conclusions from recent material. But it is a label attached to a stored item, not a state of the system that changes how storage happens. Emotional content in what a user writes does change how these systems behave, both on psychological self-report measures (⁠Ben-Zion et al., 2025⁠; ⁠Coda-Forno et al., 2023⁠) and on task performance (⁠Li et al., 2023⁠), yet it does so by shaping the response being generated in the moment rather than by altering what is retained. The user's emotional state therefore has no privileged route into what is stored or what later becomes accessible.

Encoding Specificity

What is retained depends on how material is processed at input, not merely on whether it is attended. Semantic or elaborative processing produces substantially better retention than perceptual processing of the same material, with recognition varying between .14 and .96 as a function of the orienting question alone (⁠Craik & Tulving, 1975⁠). The effect is not reducible to time on task: a structural task that took twice as long as a semantic one still yielded worse recognition, and the advantage persists under intentional learning and when participants are paid more to remember shallowly encoded items. Attention is not a separate constraint so much as a determinant of the same variable, since dividing attention at encoding produces shallower encoding; encoding is also where attention matters most, with divided attention costing 22 to 46 percent of later memory at encoding but only 1 to 13 percent at retrieval (⁠Craik et al., 1996⁠). The advantage of deep processing is not absolute, since retention depends on the match between encoding and retrieval operations (⁠Morris et al., 1977⁠; ⁠Tulving & Thomson, 1973⁠), though matched shallow processing still underperforms matched deep processing. ⁠Craik (2002)⁠ further concedes that deep processing is necessary but not sufficient, with consolidation required as a separate step, which is why this factor feeds Consolidation as well as Semantic Knowledge, Episodic Memory, and Schema Formation.

The AI question it raises

A language model by itself does nothing of this kind at the moment of use. Its weights hold what training left in them, but nothing said in a conversation is written into them, and anything it appears to recall from earlier in a session is simply text still sitting in front of it rather than something it encoded. Elaboration at storage time is a property of memory systems built around the model, and in those systems the effect is large. When the A-MEM system files a new memory, it also generates keywords, tags, and a short description of the surrounding context, builds all of that into the numerical representation it later uses to find that memory, and then goes back to revise and link the related memories already in the store. Remove that elaboration step and performance on questions that require chaining information across several memories falls from an F1 of 27.02 to 9.65, where F1 combines precision and recall into a single accuracy score (⁠Xu et al., 2025⁠). Mem0 does something comparable, pulling the salient facts out of new input and reconciling them against what is already stored through explicit add, update, and delete operations (⁠Chhikara et al., 2025⁠). The memory features now shipping in consumer assistants are layers of this same kind rather than native model capability.

04

Measuring Memory in AI

Product and Layer

The unit a user actually encounters is a product: a deployed assistant such as Claude, ChatGPT, or Gemini. A product is a configuration rather than a component. It comprises a particular model, a particular set of memory rules, a system prompt, tool access, sampling parameters, and a set of defaults. An "out-of-the-box" AI refers to a product under those default settings, which is the configuration in which most users meet a general-purpose assistant.

Within a product, memory is distributed across three separately configurable layers, distinguished by how long what they hold persists. Because they behave differently and are studied unevenly, each claim on this site is tagged to the layer it concerns, or to the product where no single layer applies. Components that shape memory behavior without persisting on a horizon of their own, including the system prompt and sampling parameters, are treated as configuration and discussed at the product level.

Weights Across deployments

What training put into the model's parameters. Fixed during inference, so nothing that happens within a conversation changes them, but modifiable between deployments through further training.

Example. Pretraining and post-training, including RLHF; fine-tuning a base model on domain data.

Context Window Within a session

Everything visible to the model during a single response: the conversation so far, the system prompt, and any documents supplied. Context is bounded, and when a session exceeds that bound the excess is truncated, dropped from the front of a sliding window, or compressed into a summary that replaces the original text. Whatever remains is discarded entirely when the session ends. This within-session compression is the closest functional analog to consolidation available in these systems, and like consolidation it is lossy, rule-governed, and determinative of what survives.

Example. The context window; in-context learning; summarization or compaction of an overlong conversation.

Memory Layer Across sessions

An external store that persists between sessions, together with the rules governing what is written to it and what is retrieved back into context.

Example. Retrieval-augmented generation over a vector database; agentic memory frameworks such as Mem0; a user-facing "remember this" feature.

Published benchmarks evaluate products, not layers. When one reports a memory failure, what was measured is a configuration.

How the layers interact, and the two kinds of memory layer, are set out on the Method page.

Level of Measurement

Each construct was assessed for how far it has been studied in existing AI systems, and placed in one of four states. Where a construct reports different states at different layers, it is counted as Indirectly Measured.

Directly Measured

A published study tests AI on this ability by name, or gives AI the same experiment psychologists use to test it in people.

Requires. Citing that study and the human experiment it follows.

Example. ImplicitMemBench on procedural memory, priming, and conditioning.

Indirectly Measured

Studies have tested something close to this ability, but under a different name, as part of a broader test, or in only some of the places an AI system holds information.

Requires. Naming the AI measure and the human ability it corresponds to. An ability measured in some places and not others is placed here, since a partial result is what that is.

Example. Semantic entropy (⁠Farquhar et al., 2024⁠) operationalizes the same resampling-and-dispersion logic as ⁠Koriat's (1993)⁠ self-consistency account, with no cross-citation between the literatures.

A Note on a Young Field

The psychology of memory is an established field with a lengthy history of empirical evaluation; research on AI memory is younger and less developed. The AI half of this work represents the most relevant research available at the time of writing, and makes no claim to be a comprehensive overview of a rapidly evolving field.

The asymmetry in evidentiary maturity between the human and AI halves of each entry is itself part of what this work documents: not only that the AI literature is younger, but that it measures at a coarser grain.

Purpose and Execution of Memory: Foundational Differences Between Human and AI Memory Architectures, and Implications

Elizabeth K. Bayardelle, PhD and Jennifer L. Thompson, PhD

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