When perception fades, the hippocampus may support implicit memory.

Steinkrauss and Slotnick (2024) conclude that current evidence is insufficient to sustain a link between implicit memory and the hippocampus. However, behavioral protocols designed to minimize visual awareness, so that memoranda are objectively invisible both at study and at test, can yield brain-based signals of implicit memory, which circumvent several of the identified constraints. Furthermore, while differences in novelty and attention complicate the interpretation of hippocampal involvement in implicit memory tasks, these processes can occur with and without conscious awareness, suggesting a more complex interplay between the hippocampus and memory-related processes than an exclusive association with consciousness would indicate.

Concerns about confounds: False memory as an explanation for a hippocampus-supported implicit eye-movement-based relational memory effect.

Steinkrauss and Slotnick (2024) propose that implicit eye-movement-based relational memory effects, predicted by hippocampal activity differences (Hannula & Ranganath, 2009), are due to an explicit false memory confound. However, the logic behind this claim is insufficiently fleshed out and alternative accounts of how false memory may have played out in this task were not considered. One such account would predict a pattern of results counter to the observed fMRI results, and another would be consistent with our original conclusions. These alternatives are described along with converging evidence from an additional fMRI study that was not considered by Steinkrauss and Slotnick.

The dead salmon strikes again: Reports of unconscious processing in the hippocampus may reflect Type-I error.

Steinkrauss and Slotnick (2024) reviewed neuroimaging studies linking the hippocampus with implicit memory. They conclude that there is no convincing evidence that the hippocampus is associated with implicit memory because prior studies are confounded by explicit memory (among other factors). Here, we ask a different yet equally important question: do reports of unconscious hippocampal activity reflect a Type-I error (i.e. a false positive)? We find that 39% of studies linking the hippocampus with implicit memory (7 of 18) do not report correcting for multiple comparisons. These results indicate that many unconscious hippocampal effects may reflect a Type-I error.

Dismissing the role of the hippocampus in implicit memory is special pleading.

Steinkrauss and Slotnick (this issue) argue against hippocampal involvement in implicit memory, bringing up some important considerations. Their critique, however, exhibits significant flaws. The argumentation is based on an ill-defined key concept of 'implicit memory,' and important theoretical context is missed. Potential confounds are brought to bear against a rather narrow selection of studies, often without explaining how exactly the studies are biased. Refining the conceptual scope, including a broader range of literature, and arguing more inclusively would provide more nuanced insights into the hippocampus's role in implicit memory.

The hippocampus and implicit memory (by any other name).

Is the hippocampus involved in implicit memory? I argue that contemporary views on hippocampal function, going beyond the classic dichotomy of explicit versus implicit, predict involvement of the hippocampus whenever flexible, predictive associations are rapidly encoded. This involvement is independent of conscious awareness. A paradigm case is statistical learning: the unconscious extraction of statistical regularities from the environment. In line with this, a substantial body of literature on contextual cueing in visual search has established hippocampal involvement in this form of implicit learning. To conclude, implicit memory (as such or by any other name) is associated with the hippocampus.

Is implicit memory associated with the hippocampus?

According to the traditional memory-systems view, the hippocampus is critical during explicit (conscious) long-term memory, whereas other brain regions support implicit (nonconscious) memory. In the last two decades, some fMRI studies have reported hippocampal activity during implicit memory tasks. The aim of the present discussion paper was to identify whether any implicit memory fMRI studies have provided convincing evidence that the hippocampus is associated with nonconscious processes without being confounded by conscious processes. Experimental protocol and analysis parameters included the stimulus type(s), task(s), measures of subjective awareness, explicit memory accuracy, the relevant fMRI contrast(s) or analysis, and confound(s). A systematic review was conducted to identify implicit memory studies that reported fMRI activity in the hippocampus. After applying exclusion criteria, 13 articles remained for analysis. We found that there were no implicit memory fMRI studies where subjective awareness was absent, explicit memory performance was at chance, and there were no confounds that could have driven the observed hippocampal activity. The confounds included explicit memory (including false memory), imbalanced attentional states between conditions (yielding activation of the default-mode network), imbalanced stimuli between conditions, and differential novelty. As such, not a single fMRI study provided convincing evidence that implicit memory was associated with the hippocampus. Neuropsychological evidence was also considered, and implicit memory deficits were caused by factors known to disrupt brain regions beyond the hippocampus, such that the behavioral effects could not be attributed to this region. The present results indicate that implicit memory is not associated with the hippocampus.

Differential effects of bilateral hippocampal CA3 damage on the implicit learning and recognition of complex event sequences.

Learning regularities in the environment is a fundament of human cognition, which is supported by a network of brain regions that include the hippocampus. In two experiments, we assessed the effects of selective bilateral damage to human hippocampal subregion CA3, which was associated with autobiographical episodic amnesia extending ~50 years prior to the damage, on the ability to recognize complex, deterministic event sequences presented either in a spatial or a non-spatial configuration. In contrast to findings from related paradigms, modalities, and homologue species, hippocampal damage did not preclude recognition memory for an event sequence studied and tested at four spatial locations, whereas recognition memory for an event sequence presented at a single location was at chance. In two additional experiments, recognition memory for novel single-items was intact, whereas the ability to recognize novel single-items in a different location from that presented at study was at chance. The results are at variance with a general role of the hippocampus in the learning and recognition of complex event sequences based on non-adjacent spatial and temporal dependencies. We discuss the impact of the results on established theoretical accounts of the hippocampal contributions to implicit sequence learning and episodic memory.

Some young adults hyper-bind too: Attentional control relates to individual differences in hyper-binding.

Hyper-binding - the erroneous encoding of target and distractor information into associative pairs in memory - has been described as a unique age effect caused by declines in attentional control. Previous work has found that, on average, young adults do not hyper-bind. However, if hyper-binding is caused by reduced attentional control, then young adults with poor attention regulation should also show evidence of hyper-binding. We tested this question with an individual differences approach, using a battery of attentional control tasks and relating this to individual differences in hyper-binding. Participants (N = 121) completed an implicit associative memory test measuring memory for both target-distractor (i.e., hyper-binding) and target-target pairs, followed by a series of tasks measuring attentional control. Our results show that on average, young adults do not hyper-bind, but as predicted, those with poor attentional control show a larger hyper-binding effect than those with good attentional control. Exploratory analyses also suggest that individual differences in attentional control relate to susceptibility to interference at retrieval. These results support the hypothesis that hyper-binding in older adults is due to age-related declines in attentional control, and demonstrate that hyper-binding may be an issue for any individual with poor attentional control, regardless of age.

Age differences in priming as a function of processing at encoding.

It is unclear whether implicit memory (priming) is affected by aging. Some studies have reported no difference between young and older adults, while others have uncovered reliable reductions. An important factor that may explain these discrepancies is the manner of encoding. Processing requirements (perceptual/conceptual) have varied considerably between studies, yet processing abilities are not equally affected by aging. This study examined whether processing during encoding moderates age effects on priming. Young and older participants studied object-word pairs and made natural/manufactured (conceptual) and left/right rotation (perceptual) judgements in relation to the word or object. Objects served as targets on a subsequent continuous identification with recognition task to assess priming and recognition. Priming and recognition were greater in young than older adults for attended items, with a larger effect size in the conceptual than the perceptual condition. Findings suggest that age differences in priming may be a function of processing at encoding.

The Influence of Memory on Visual Perception in Infants, Children, and Adults.

Perception is not an independent, in-the-moment event. Instead, perceiving involves integrating prior expectations with current observations. How does this ability develop from infancy through adulthood? We examined how prior visual experience shapes visual perception in infants, children, and adults. Using an identical task across age groups, we exposed participants to pairs of colorful stimuli and implicitly measured their ability to discriminate relative saturation levels. Results showed that adult participants were biased by previously experienced exemplars, and exhibited weakened in-the-moment discrimination between different levels of saturation. In contrast, infants and children showed less influence of memory in their perception, and they actually outperformed adults in discriminating between current levels of saturation. Our findings suggest that as humans develop, their perception relies more on prior experience and less on current observation.

Learning during sleep in humans - A historical review.

Sleep helps to consolidate previously acquired memories. Whether new information such as languages and other useful skills can also be learned during sleep has been debated for over a century, however, the sporadic studies' different objectives and varied methodologies make it difficult to draw definitive conclusions. This review provides a comprehensive overview of the history of sleep learning research conducted in humans, from its empirical beginnings in the 1940s to the present day. Synthesizing the findings from 51 research papers, we show that several studies support the notion that simpler forms of learning, such as habituation and conditioning, are possible during sleep. In contrast, the findings for more complex, applied learning (e.g., learning a new language during sleep) are more divergent. While there is often an indication of processing and learning during sleep when looking at neural markers, behavioral evidence for the transfer of new knowledge to wake remains inconclusive. We close by critically examining the limitations and assumptions that have contributed to the discrepancies in the literature and highlight promising new directions in the field.

Exploring why "memory loss" is a misleading descriptor of people living with dementia and can lead to dysfunctional care.

Amidst goals for prevention and improved treatment for people living with dementia, much remains needed to enhance the quality of life of those currently diagnosed, especially the transfer of accurate information from professionals to the public. Although many healthcare professionals understand the various types of memory and which are likely to be more affected than others during the progression of dementia, lay persons are more frequently unaware of that important information. The terms used to describe the symptoms of dementia can have a great impact on perceptions of faculties that are absent, compromised, or preserved. Understanding the nuances of preserved memory faculties and other cognitive abilities retained by persons with dementia is important in this regard. The term "memory loss" as a descriptor of the syndrome of dementia and ascribing it to persons with dementia connotes an inability to form new memories and participate in meaningful social interactions, which is detrimental to their personhood. From a multidisciplinary approach drawn from neurology, neurobiology, psychology, and case vignettes, we aim herein to highlight the ways in which the term "memory loss" can be inaccurate, counterproductive and potentially promote dementia-related misperceptions, malignant positioning and malignant social psychology. Persons with dementia unequivocally struggle with explicit memory, or recalling on demand, but retain implicit memory, as evidenced by research and everyday actions. Therefore, we propose the use of alternative medical language to reflect accurately memory impairment and preservation of some important memory capabilities.

No evidence of fast mapping in healthy adults using an implicit memory measure: failures to replicate the lexical competition results of Coutanche and Thompson-Schill (2014).

Fast mapping (FM) is a hypothetical, incidental learning process that allows rapid acquisition of new words. Using an implicit reaction time measure in a FM paradigm, Coutanche and Thompson-Schill (Coutanche, M. N., & Thompson-Schill, S. L. (2014). Fast mapping rapidly integrates information into existing memory networks. Journal of Experimental Psychology: General, 143(6), 2296-2303. https://doi.org/10.1037/xge0000020) showed evidence of lexical competition within 10 min of non-words being learned as names of unknown items, consistent with same-day lexicalisation. Here, Experiment 1 was a methodological replication (N = 28/group) that found no evidence of this RT competition effect. Instead, a post-hoc analysis suggested evidence of semantic priming. Experiment 2 (N = 60/group, online study, pre-registered on OSF) tested whether semantic priming remained when making the stimulus set fully counterbalanced. No evidence for either lexical competition nor semantic priming was detected. Experiment 3 (n = 64, online study, pre-registered on OSF) tested whether referent (a)typicality boosted lexical competition (Coutanche, M. N., & Koch, G. E. (2017). Variation across individuals and items determine learning outcomes from fast mapping. Neuropsychologia, 106, 187-193. https://doi.org/10.1016/j.neuropsychologia.2017.09.029), but again no evidence of lexical competition was observed, and Bayes Factors for the data combined across all three experiments supported the hypothesis that there is no effect of lexical competition under FM conditions. These results, together with our previous work, question whether fast mapping exists in healthy adults, at least using this specific FM paradigm.

Moderate-intensity cardiovascular exercise performed before motor practice attenuates offline implicit motor learning in stroke survivors but not age-matched neurotypical adults.

The acute impact of cardiovascular exercise on implicit motor learning of stroke survivors is still unknown. We investigated the effects of cardiovascular exercise on implicit motor learning of mild-moderately impaired chronic stroke survivors and neurotypical adults. We addressed whether exercise priming effects are time-dependent (e.g., exercise before or after practice) in the encoding (acquisition) and recall (retention) phases. Forty-five stroke survivors and 45 age-matched neurotypical adults were randomized into three sub-groups: BEFORE (exercise, then motor practice), AFTER (motor practice, then exercise), and No-EX (motor practice alone). All sub-groups practiced a serial reaction time task (five repeated and two pseudorandom sequences per day) on three consecutive days, followed 7 days later by a retention test (one repeated sequence). Exercise was performed on a stationary bike, (one 20-min bout per day) at 50% to 70% heart rate reserve. Implicit motor learning was measured as a difference score (repeated-pseudorandom sequence response time) during practice (acquisition) and recall (delayed retention). Separate analyses were performed on the stroke and neurotypical groups using linear mixed-effects models (participant ID was a random effect). There was no exercise-induced benefit on implicit motor learning for any sub-group. However, exercise performed before practice impaired encoding in neurotypical adults and attenuated retention performance of stroke survivors. There is no benefit to implicit motor learning of moderately intense cardiovascular exercise for stroke survivors or age-matched neurotypical adults, regardless of timing. Practice under a high arousal state and exercise-induced fatigue may have attenuated offline learning in stroke survivors.

An ERP measure of non-conscious memory reveals dissociable implicit processes in human recognition using an open-source automated analytic pipeline.

Non-conscious processing of human memory has traditionally been difficult to objectively measure and thus understand. A prior study on a group of hippocampal amnesia (N = 3) patients and healthy controls (N = 6) used a novel procedure for capturing neural correlates of implicit memory using event-related potentials (ERPs): old and new items were equated for varying levels of memory awareness, with ERP differences observed from 400 to 800 ms in bilateral parietal regions that were hippocampal-dependent. The current investigation sought to address the limitations of that study by increasing the sample of healthy subjects (N = 54), applying new controls for construct validity, and developing an improved, open-source tool for automated analysis of the procedure used for equating levels of memory awareness. Results faithfully reproduced prior ERP findings of parietal effects that a series of systematic control analyses validated were not contributed to nor contaminated by explicit memory. Implicit memory effects extended from 600 to 1000 ms, localized to right parietal sites. These ERP effects were found to be behaviorally relevant and specific in predicting implicit memory response times, and were topographically dissociable from other traditional ERP measures of implicit memory (miss vs. correct rejections) that instead occurred in left parietal regions. Results suggest first that equating for reported awareness of memory strength is a valid, powerful new method for revealing neural correlates of non-conscious human memory, and second, behavioral correlations suggest that these implicit effects reflect a pure form of priming, whereas misses represent fluency leading to the subjective experience of familiarity.

What sticks after statistical learning: The persistence of implicit versus explicit memory traces.

Statistical learning is a powerful mechanism that extracts even subtle regularities from our information-dense worlds. Recent theories argue that statistical learning can occur through multiple mechanisms-both the conventionally assumed automatic process that precipitates unconscious learning, and an attention-dependent process that brings regularities into conscious awareness. While this view has gained popularity, there are few empirical dissociations of the hypothesized implicit and explicit forms of statistical learning. Here we provide strong evidence for this dissociation in two ways. First, we show in healthy adults (N = 60) that implicit and explicit traces have divergent consolidation trajectories, with implicit knowledge of structure strengthened over a 24-h period, while precise explicit representations tend to decay. Second, we demonstrate that repeated testing strengthens the retention of explicit representations but that implicit statistical learning is uninfluenced by testing. Together these dissociations provide much needed support for the reconceptualization of statistical learning as a multi-component construct.

Collective Trauma, Implicit Memories, the Body, and Active Imagination in Jungian Analysis1.

This presentation attempts to show the healing potential underlying the inclusion of the patient's body in the analytic process, while honouring and revisiting the understanding of the psyche-body connection described by Jung in his early work. In addition, the author offers reflections on the impact of collective trauma whose aftermath, among others, has been the disappearance of thousands of people, consequently breaking the family genealogy, leaving hundreds of children stripped of their roots and true identity. Referencing clinical material, the author describes how the process of translation and integration-from the sensory-perceptual to the conceptual-symbolic-can be halted on account of collective trauma occurring at an early stage in development. Moreover, it is shown how the potential of the archetype or image schema, linked to the somatic-affective early experiences encoded as implicit memories, can be recovered, when Embodied Active Imagination is included in the analytic work. The patient's bodily gestures and somatic experience may bridge the gap between the preverbal-implicit knowledge and the emergence of emotions and images that allow for the creation of a new symbolic narrative.

Cette présentation vise à montrer le potentiel de guérison qu'il y a quand on inclut le corps du patient dans le processus analytique. En même temps la présentation fait honneur et revisite la compréhension du lien psyché-soma que Jung a décrite dans ses écrits précoces. De plus, l'auteur offre des réflexions sur l'impact de traumatismes collectifs dont les suites ont été - entre autres - la disparition de milliers de personnes, et en conséquence la cassure de la généalogie familiale, laissant des centaines d'enfants privés de leurs racines et de leur identité véritable. En faisant référence au matériel clinique l'auteur décrit comment le processus de traduction et d'intégration - du sensoriel-perceptuel au conceptuel-symbolique - peut être stoppé du fait d'un traumatisme collectif se produisant à un stade précoce du développement. D'autre part, il est montré comment le potentiel de l'archétype ou schéma-image, lié aux expériences précoces affectives et somatiques codées en tant que souvenirs implicites, peut être retrouvé quand on inclut l'Imagination Active Incarnée dans le travail analytique. Les mouvements du corps du patient et son expérience somatique peuvent agir comme une passerelle entre la connaissance implicite préverbale et l'émergence d'émotions et d'images qui permettent la création d'un récit symbolique nouveau.

Esta presentación propone mostrar el potencial curativo que subyace a la inclusión del cuerpo del paciente en el proceso analítico, al tiempo que honra y revisita la comprensión de la conexión psique-cuerpo descripta por Jung en sus primeros trabajos. Además, la autora ofrece reflexiones sobre el impacto del trauma colectivo cuyas secuelas, entre otras, han sido la desaparición de miles de personas, rompiendo en consecuencia la genealogía familiar y dejando a cientos de niños despojados de sus raíces y de su verdadera identidad. Tomando como referencia material clínico, la autora describe cómo el proceso de traducción e integración, de lo sensorio-perceptivo a lo conceptual-simbólico, puede detenerse debido a que el trauma colectivo se produce en una fase temprana del desarrollo. Se muestra, a su vez, cómo puede recuperarse el potencial del arquetipo o esquema-imagen, vinculado a las tempranas experiencias somato-afectivas codificadas como memorias implícitas, cuando se incluye la Imaginación Activa Corporizada en el trabajo analítico. Los gestos corporales y la experiencia somática del paciente pueden tender un puente entre el conocimiento preverbal-implícito y la emergencia de emociones e imágenes que permite la creación de una nueva narrativa simbólica.

Learning strategy differentially impacts memory connections in children and adults.

Even once children can accurately remember their experiences, they nevertheless struggle to use those memories in flexible new ways-as in when drawing inferences. However, it remains an open question as to whether the developmental differences observed during both memory formation and inference itself represent a fundamental limitation on children's learning mechanisms, or rather their deployment of suboptimal strategy. Here, 7-9-year-old children (N = 154) and young adults (N = 130) first formed strong memories for initial (AB) associations and then engaged in one of three learning strategies as they viewed overlapping (BC) pairs. We found that being told to integrate-combine ABC during learning-both significantly improved children's ability to explicitly relate the indirectly associated A and C items during inference and protected the underlying pair memories from forgetting. However, this finding contrasted with implicit evidence for memory-to-memory connections: Adults and children both formed A-C links prior to any knowledge of an inference test-yet for children, such links were most apparent when they were told to simply encode BC, not integrate. Moreover, the accessibility of such implicit links differed between children and adults, with adults using them to make explicit inferences but children only doing so for well-established direct AB pairs. These results suggest that while a lack of integration strategy may explain a large share of the developmental differences in explicit inference, children and adults nevertheless differ in both the circumstances under which they connect interrelated memories and their ability to later leverage those links to inform flexible behaviours. RESEARCH HIGHLIGHTS: Children and adults view AB and BC pairs related through a shared item, B. This provides an opportunity for learners to connect A-C in memory. Being encouraged to integrate ABC during learning boosted performance on an explicit test of A-C connections (children and adults) and protected from forgetting (children). Children and adults differed in when implicit A-C connections were formed-occurring primarily when told to separately encode BC (children) versus integrate (adults), respectively. Adults used implicit A-C connections to facilitate explicit judgments, while children did not. Our results suggest developmental differences in the learning conditions promoting memory-to-memory connections.

Age and processing effects on perceptual and conceptual priming.

Explicit (declarative) memory declines with age, but age effects on implicit (nondeclarative) memory are debated. Some studies have reported null changes in implicit memory (e.g., priming in word-fragment completion, perceptual identification, category exemplar generation) with age, while others have uncovered declines. One factor that may account for these discrepancies is processing. Evidence suggests that conceptual and perceptual processes are not equally affected by ageing, yet processing requirements have varied greatly between studies. Processing may moderate age effects on priming, but no study has systematically examined this issue. This registered report presents an experiment to manipulate processing (conceptual / perceptual) during incidental encoding of words, prior to measures of perceptual (perceptual identification) and conceptual (category verification) priming. The perceptual and conceptual priming tasks were matched on all characteristics except processing, making them highly comparable. The four orthogonal conditions (perceptual encoding, perceptual test [PP]; conceptual encoding, perceptual test [CP]; perceptual encoding, conceptual test [PC]; conceptual encoding, conceptual test [CC]) were designed to clarify situations in which age effects on implicit memory emerge, which holds important practical and theoretical implications. Significant effects of Age, Test, and an Age × Processing interaction emerged. Priming was greater in young than older adults and on the perceptual than the conceptual test, but in contrast to the predictions, the age difference was only significant when prior encoding was perceptual (i.e., in the PP and CP conditions).

Implicit processes enhance cognitive abilities in mild cognitive impairment.

Previous work has shown that older adults with typical age-related memory changes (i.e., without cognitive impairment) pick up irrelevant information implicitly, and unknowingly use that information when it becomes relevant to a later task. Here, we address the possibility that implicit processes play a similarly beneficial role in the cognitive abilities of individuals with amnestic mild cognitive impairment (aMCI). Twenty-two individuals with aMCI and 22 matched controls participated in a picture judgment task while instructed to ignore distractions in the form of word/non-word letter strings. Memory for the distracting words was later tested with a word-fragment completion task. Both groups showed a priming effect, that is, they were significantly more likely to solve fragments of previously presented than non-presented words. However, the aMCI group had significantly higher scores than the older adults without cognitive impairment, t(42) = 2.16, p < .05, Cohen's d = 0.67. Our findings suggest that individuals with aMCI can enhance their performance on an explicit cognitive task, in this case, word-fragment completion, if previously exposed to the relevant information implicitly, opening up possible interventions aimed at this population.