| 1. |
- Araújo, Susana, et al.
(författare)
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Lexical and sublexical orthographic processing: An ERP study with skilled and dyslexic adult readers.
- 2015
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Ingår i: Brain and Language. - : Elsevier BV. - 1090-2155 .- 0093-934X. ; 141, s. 16-27
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Tidskriftsartikel (refereegranskat)abstract
- This ERP study investigated the cognitive nature of the P1-N1 components during orthographic processing. We used an implicit reading task with various types of stimuli involving different amounts of sublexical or lexical orthographic processing (words, pseudohomophones, pseudowords, nonwords, and symbols), and tested average and dyslexic readers. An orthographic regularity effect (pseudowords-nonwords contrast) was observed in the average but not in the dyslexic group. This suggests an early sensitivity to the dependencies among letters in word-forms that reflect orthographic structure, while the dyslexic brain apparently fails to be appropriately sensitive to these complex features. Moreover, in the adults the N1-response may already reflect lexical access: (i) the N1 was sensitive to the familiar vs. less familiar orthographic sequence contrast; (ii) and early effects of the phonological form (words-pseudohomophones contrast) were also found. Finally, the later N320 component was attenuated in the dyslexics, suggesting suboptimal processing in later stages of phonological analysis.
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| 2. |
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| 3. |
- Bramao, Ines, et al.
(författare)
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Benefits and costs of context reinstatement in episodic memory : An ERP study
- 2017
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Ingår i: Journal of Cognitive Neuroscience. - : MIT Press - Journals. - 1530-8898 .- 0898-929X. ; 29:1, s. 52-64
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated context-dependent episodic memory retrieval. An influential idea in the memory literature is that performance benefits when the retrieval context overlaps with the original encoding context. However, such memory facilitation may not be driven by the encoding-retrieval overlap per se but by the presence of diagnostic features in the reinstated context that discriminate the target episode from competing episodes. To test this prediction, the encoding-retrieval overlap and the diagnostic value of the context were manipulated in a novel associative recognition memory task. Participants were asked to memorize word pairs presented together with diagnostic (unique) and nondiagnostic (shared) background scenes. At test, participants recognized the word pairs in the presence and absence of the previously encoded contexts. Behavioral data show facilitated memory performance in the presence of the original context but, importantly, only when the context was diagnostic of the target episode. The electrophysiological data reveal an early anterior ERP encoding-retrieval overlap effect that tracks the cost associated with having nondiagnostic contexts present at retrieval, that is, shared by multiple previous episodes, and a later posterior encoding-retrieval overlap effect that reflects facilitated access to the target episode during retrieval in diagnostic contexts. Taken together, our results underscore the importance of the diagnostic value of the context and suggest that context-dependent episodic memory effects are multiple determined.
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| 4. |
- Bramao, Ines, et al.
(författare)
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Electrophysiological signatures revealing the temporal dynamics of episodic retrieval
- 2022
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Konferensbidrag (refereegranskat)abstract
- Episodic memory enables mental time travel, allowing us to relive specific, personally experienced events tied in time and place. This feat of human memory is considered to be dependent on the reinstatement of the cortical patterns that were active at the time of encoding. A growing body of recent literature has provided support for this idea by showing that retrieval success co-varies with the neural encoding patterns being reinstated at the time of retrieval. In this presentation, we will discuss findings from multivariate pattern analysis of electrophysiological data revealing the temporal dynamics of such reinstatement during retrieval and its consequences for episodic remembering. First, we will discuss both benefits and costs of cortical pattern reinstatement. Accumulating evidence has shown that memory typically benefits when the neural patterns established during encoding are reinstated during retrieval. However, our data show that reinstatement can also have detrimental effects on later episodic remembering depending on which aspects of the event are called-for. Next, we will show that contextual background features of an encoding episode are reinstated during selective retrieval even when such information is task-irrelevant. These data elucidate that context reinstatement tracks retrieval competition between similar episodes and interference resolution. Combined, our data elucidate the temporal dynamics of episodic remembering and shed new light on encoding and retrieval interactions in episodic memory.
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| 5. |
- Bramao, Ines, et al.
(författare)
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Encoding contexts are incidentally reinstated during competitive retrieval and track the temporal dynamics of memory interference
- 2022
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Ingår i: Cerebral Cortex. - : Oxford University Press (OUP). - 1460-2199 .- 1047-3211. ; 32:22, s. 5020-5035
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Tidskriftsartikel (refereegranskat)abstract
- The ability to remember an episode from our past is often hindered by competition from similar events. For example, if we want to remember the article a colleague recommended during the last lab-meeting, we may need to resolve interference from other article recommendations from the same colleague. This study investigates if the contextual features specifying the encoding episodes are incidentally reinstated during competitive memory retrieval. Competition between memories was created through the AB/AC interference paradigm. Individual word-pairs were presented embedded in a slowly drifting real-word like context. Multivariate pattern analysis (MVPA) of high temporal-resolution electroencephalographic (EEG) data was used to investigate context reactivation during memory retrieval. Behaviorally, we observed proactive (but not retroactive) interference; that is, performance for AC competitive retrieval was worse compared to a control DE non-competitive retrieval, whereas AB retrieval did not suffer from competition. Neurally, proactive interference was accompanied by an early reinstatement of the competitor context and interference resolution was associated with the ensuing reinstatement of the target context. Together, these findings provide novel evidence showing that the encoding contexts of competing discrete events are incidentally reinstated during competitive retrieval and that such reinstatement tracks retrieval competition and subsequent interference resolution.
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| 6. |
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| 7. |
- Bramao, Ines, et al.
(författare)
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Mental reinstatement of encoding context improves episodic remembering
- 2017
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Ingår i: Cortex. - : Elsevier BV. - 0010-9452. ; 94, s. 15-26
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates context-dependent memory retrieval. Previous work has shown that physically re-experiencing the encoding context at retrieval improves memory accessibility. The current study examined if mental reconstruction of the original encoding context would yield parallel memory benefits. Participants performed a cued-recall memory task, preceded either by a mental or by a physical context reinstatement task, and we manipulated whether the context reinstated at retrieval overlapped with the context of the target episode. Both behavioral and electrophysiological measures of brain activity showed strong encoding-retrieval (E-R) overlap effects, with facilitated episodic retrieval when the encoding and retrieval contexts overlapped. The electrophysiological E-R overlap effect was more sustained and involved more posterior regions when context was mentally compared with physically reinstated. Additionally, a time-frequency analysis revealed that context reinstatement alone engenders recollection of the target episode. However, while recollection of the target memory is readily prompted by a physical reinstatement, target recollection during mental reinstatement is delayed and depends on the gradual reconstruction of the context. Taken together, our results show facilitated episodic remembering also when mentally reinstating the encoding context; and that such benefits are supported by both shared and partially non-overlapping neural mechanisms when the encoding context is mentally reconstructed as compared with physically presented at the time of retrieval.
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| 8. |
- Bramao, Ines, et al.
(författare)
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Neural correlates of mental context reinstatement supporting episodic memory retrieval
- 2016
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Konferensbidrag (refereegranskat)abstract
- This study investigated if mental reinstatement of an encoding context during retrieval increases memory accessibility. Participants performed a cued-recall memory task where the overlap between encoding and retrieval context and the nature of context reinstatement (mental versus physical) were manipulated. Memory performance improved when the encoding-retrieval context overlapped in a comparable way for mental and physical context reinstatement. However, compared to physical reinstatement, mental reinstatement was characterized by later and more sustained ERP effects. Together, our results suggest that the access to episodic memories can be facilitated also by mentally reinstating the encoding context, and furthermore that such benefits may be supported by processes differently engaged than when the encoding context is physically re-presented at the time of retrieval.
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| 9. |
- Bramao, Ines, et al.
(författare)
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Neural pattern classification reveals the temporal dynamics of competitive memory retrieval
- 2019
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Konferensbidrag (refereegranskat)abstract
- Resolution of interference between competing memories is often critical for remembering. This study employed multivariate pattern analysis (MVPA) of electroencephalographic (EEG) data to investigate the temporal dynamics of retrieval competition and competition resolution. Competition between memories was created through the AB/AC interference paradigm. Memory retrieval of competitive AB and AC cue-associate word pairs was compared with non-competitive DE word pairs. Behavioural results showed worse memory performance for AC compared with DE word pairs, but comparable performance for AB and DE word pairs, revealing proactive without retroactive interference. Critically, the AB, AC and DE word pairs were encoded embedded in a movie with a distinct theme (first-person perspective of underwater, forest, and city environments). We trained classifiers to discriminate patterns of brain activity associated with the movies at encoding. The classifiers were later applied during memory retrieval to track memory reactivation. In an early cue time window, where only the word cue was presented (i.e. A or D), we observed classification performance for non-competitive retrieval, revealing target reactivation, but no classification for competitive retrieval, presumably due to the simultaneous reactivation of target and competitor memories. In a following probe time window, when participants were given a first-letter probe to retrieve the target word (i.e. B/C/E), we observed classification performance ~700 ms after probe onset for the competitive retrieval, revealing the time course of competition resolution. Importantly, classification accuracy in this late time window co-varied with memory performance, that is, with the resolution of proactive interference. This study offers novel insights into the time course of memory competition and competition resolution.
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| 10. |
- Bramao, Ines, et al.
(författare)
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Neural pattern classification tracks transfer-appropriate processing in episodic memory
- 2018
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Ingår i: eNeuro. - 2373-2822.
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Tidskriftsartikel (refereegranskat)abstract
- The transfer-appropriate processing (TAP) account holds that episodic memory depends on the overlap between encoding and retrieval processing. In the current study, we employed multivariate pattern analysis (MVPA) of electroencephalography to examine the relevance of spontaneously engaged visual processing during encoding for later retrieval. Human participants encoded word- picture associations, where the picture could be a famous face, a landmark, or an object. At test, we manipulated the retrieval demands by asking participants to retrieve either visual or verbal information about the pictures. MVPA revealed classification between picture categories during early perceptual stages of encoding (∼170 ms). Importantly, these visual category-specific neural patterns were predictive of later episodic remembering, but the direction of the relationship was contingent on the particular retrieval demand of the memory task: a benefit for the visual and a cost for the verbal. A reinstatement of the category-specific neural patterns established during encoding was observed during retrieval, and again the relationship with behavior varied with retrieval demands. Reactivation of visual representations during retrieval was associated with better memory in the visual task, but with lower performance in the verbal task. Our findings support and extend the TAP account by demonstrating that processing of particular aspects during memory formation can also have detrimental effects on later episodic remembering when other aspects of the event are called-for and shed new light on encoding and retrieval interactions in episodic memory.
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| 11. |
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| 12. |
- Inácio, Filomena, et al.
(författare)
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Implicit sequence learning is preserved in dyslexic children
- 2018
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Ingår i: Annals of Dyslexia. - : Springer Science and Business Media LLC. - 0736-9387 .- 1934-7243. ; 68:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the implicit sequence learning abilities of dyslexic children using an artificial grammar learning task with an extended exposure period. Twenty children with developmental dyslexia participated in the study and were matched with two control groups—one matched for age and other for reading skills. During 3 days, all participants performed an acquisition task, where they were exposed to colored geometrical forms sequences with an underlying grammatical structure. On the last day, after the acquisition task, participants were tested in a grammaticality classification task. Implicit sequence learning was present in dyslexic children, as well as in both control groups, and no differences between groups were observed. These results suggest that implicit learning deficits per se cannot explain the characteristic reading difficulties of the dyslexics.
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| 13. |
- Jiang, Jiefeng, et al.
(författare)
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Temporal Dynamics of Memory-guided Cognitive Control and Generalization of Control via Overlapping Associative Memories
- 2020
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Ingår i: The Journal of Neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 40:11, s. 2343-2356
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Tidskriftsartikel (refereegranskat)abstract
- Goal-directed behavior can benefit from proactive adjustments of cognitive control that occur in anticipation of forthcoming cognitive control demands (CCD). Predictions of forthcoming CCD are thought to depend on learning and memory in two ways: First, through direct experience, associative encoding may link previously experienced CCD to its triggering item, such that subsequent encounters with the item serve to cue retrieval of (i.e., predict) the associated CCD. Second, in the absence of direct experience, pattern completion and mnemonic integration mechanisms may allow CCD to be generalized from its associated item to other items related in memory. While extant behavioral evidence documents both types of CCD prediction, the neurocognitive mechanisms giving rise to these predictions remain largely unexplored. Here, we tested two hypotheses: (1) memory-guided predictions about CCD precede control adjustments due to the actual CCD required to perform, and (2) generalization of CCD can be accomplished through integration mechanisms that link partially overlapping CCD—item and item—item associations in memory. Supporting these hypotheses, the temporal dynamics of theta and alpha power in human electroencephalography data (n=43, 26 females) revealed that an associative CCD effect emerges earlier than interaction effects involving actual CCD. Furthermore, generalization of CCD from one item (X) to another item (Y) was predicted by a decrease in alpha power following the presentation of the X—Y pair. These findings advance understanding of the mechanisms underlying memory-guided adjustments of cognitive control.
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| 14. |
- Johansson, Mikael, et al.
(författare)
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Neural pattern classification tracks transfer-appropriate processing in episodic memory
- 2018
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Konferensbidrag (refereegranskat)abstract
- The transfer-appropriate processing (TAP) account holds that episodic memory depends on the overlap between encoding and retrieval processing (e.g., perceptual or conceptual). In the current study, we employed multivariate pattern analysis (MVPA) of electroencephalography to examine the relevance of spontaneously engaged processing during encoding for later retrieval. Participants encoded word-picture associations, where the picture could be a famous face, a landmark, or an object. At test, we manipulated the retrieval demands by asking participants to retrieve either visual or verbal information about the pictures. MVPA revealed classification between picture categories during early perceptual stages of encoding (~170 ms). Importantly, these visual category-specific neural patterns were predictive of later episodic remembering, but the direction of the relationship was contingent on the particular retrieval demand of the memory task: a benefit for the visual and a cost for the verbal. A reinstatement of the category-specific neural patterns established during encoding was observed during retrieval, and again the relationship with behavior varied with retrieval demands. Reactivation of visual representations during retrieval was associated with better memory in the visual task, but lower memory performance in the verbal task. Taken together, our findings provide novel evidence in favor of the TAP account and further demonstrate that processing of particular aspects during memory formation can have detrimental effects on later episodic remembering when other aspects of the event are called-for.
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| 15. |
- Johansson, Roger, et al.
(författare)
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How the Brain Constructs and Maintains Coherent Episodic Memories through Eye Movements
- 2024
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Konferensbidrag (refereegranskat)abstract
- The process of constructing, maintaining, and reconstructing episodic memories is closely linked to the temporal dynamics of visual exploration through sequences of eye movements (Johansson et al., 2022; Nikolaev et al., 2023). However, the neural mechanisms that mediate relational memory across eye movements are not yet fully understood. This study presented participants with a series of visuospatial events, each consisting of six distinct elements (faces, places, objects) positioned in different screen locations. This setup allowed for the identification and analysis of various types of inter-element associations. During a 10-second encoding phase, participants visually explored each event. Following this, the visual stimuli were removed, leaving participants with a 10-second “looking-at-nothing”-phase, where they had to retain the event and continue forming and recalling the visuospatial relationships among the elements. EEG and eye movement data were collected during the intervals with and without visual information. Finally, an associative memory test assessed memory for event-specific inter-element relationships. The results showed that the vividness of memory during the interval without visual information correlated with the amount of inter-element gaze transitions. These specific gaze transitions predicted subsequent memory for the corresponding inter-element associations and were related to changes in fixation-related neural activity observed in the desynchronization of alpha and synchronization of theta. This study is the first, to our knowledge, to identify at a fixation level the neural signatures subserving the inter-element linking process of dynamically constructing and maintaining coherent episodic memories across eye movements in the absence of visual input.
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| 16. |
- Johansson, Roger, et al.
(författare)
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Neurocognitive bases for the functional role of gaze direction during episodic memory retrieval
- 2018
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Konferensbidrag (refereegranskat)abstract
- Previous research has established that when engaged in episodic memory retrieval, people frequently look at locations associated with the sought-after memory trace, even if those locations no longer contain any information. While it has been further demonstrated that gaze positions showing compatibility between encoding and retrieval increase the likelihood of successful remembering (Johansson & Johansson, 2014), virtually nothing is known about the neurocognitive bases subserving this “looking at nothing” effect. The present study combined electroencephalography (EEG) and eye-tracking to investigate oscillatory brain activity for 30 participants who retrieved information from a previously encoded spatial arrangement of objects. Critically, participants were directed to fixate on a location of a blank screen, where the location was either congruent or incongruent with the original encoding location of the to-be-retrieved object. The results replicate previous findings, by showing superior episodic memory performance when looking at a congruent location, and further demonstrate that this facilitatory effect of gaze direction is associated with increased cortical desynchronization in the alpha/beta-band. Such desynchronization of oscillatory power in the alpha/beta band is considered to reflect successful encoding and retrieval of an episodes’ sensory information (e.g., Hanslmayr, Staresina, & Bowman, 2016). Gaze direction showing compatibility between encoding and retrieval would thus increase the specificity of neural reactivation and ultimately increase the likelihood of successful remembering. To our knowledge, this is the first causal evidence that gaze direction is functionally relevant for cortical reconstruction during episodic remembering.
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| 17. |
- Karlsson, Anna, et al.
(författare)
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Electrophysiological correlates of episodic memory retrieval are material sensitive
- 2016
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Konferensbidrag (refereegranskat)abstract
- It remains unclear whether the event-related potential (ERP) correlates of episodic memory are modulated by the type of information retrieved. In two experiments, we recorded electrophysiological brain activity while participants discriminated between old and new items from three different stimulus categories (faces, objects, and words). In the first experiment, we used a randomized event-related design, whereas in the second experiment we used a block design. In both experiments, analyses of the electrophysiological data revealed robust ERP old/new effects for all types of material that differed in their qualitative characteristics, including topographical distribution. Our findings suggest that non-overlapping neural mechanisms support retrieval of mnemonic information differing in terms of perceptual and lexical characteristics.
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| 18. |
- Kerrén, Casper, et al.
(författare)
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Strategic retrieval prevents memory interference: the temporal dynamics of retrieval orientation
- 2021
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Ingår i: Neuropsychologia. - : Elsevier BV. - 1873-3514 .- 0028-3932. ; 154
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Tidskriftsartikel (refereegranskat)abstract
- Resolving interference between overlapping memories is crucial to remember the past. This study tests the novel prediction that orienting search focus benefits goal-relevant retrieval by reducing competition from unwanted memories. In a modified retrieval-practice paradigm, participants encoded word-pairs in one of two encoding tasks. Critically, to evaluate whether this retrieval orientation (RO) reduces memory interference, target and competitor memories were always related to different encoding tasks. At retrieval, instructions were provided for half of the blocks with the intention to bias remembering towards items encoded with one of the ROs. Behavioural data show that adopting an RO improved target accessibility, strengthened the testing effect, and reduced retrieval-induced forgetting (RIF) of competitors. Specifically, RIF – typically attributed to inhibitory control of memory interference – was prominent when no retrieval orientation (NRO) instruction was provided. Furthermore, a neural correlate of RO was calculated by training a linear discriminant analysis (LDA) to discriminate the electroencephalographic (EEG) spatial brain patterns correspondent to the two ROs over the time course of selective retrieval. RO was characterised by increases in the theta and decreases in the beta frequency band, evident both before and after category-cue onset. While the pre-cue RO reinstatement effect predicted both immediate retrieval-practice success and later target accessibility, the post-cue effect predicted disengagement of inhibitory control, such that participants showing a stronger RO reinstatement effect showed lower levels of RIF. These data suggest that strategically orienting search focus during retrieval both increases target memory accessibility and reduces memory interference, which consequently protects related memories from inhibition and later forgetting. Furthermore, they also highlight the roles of theta and beta oscillations in establishing and maintaining a task-relevant bias towards target memory representations during competitive memory retrieval.
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| 19. |
- Liu, Zhenghao, et al.
(författare)
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Remembering the past during new learning: the temporal dynamics of integrative encoding
- 2022
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Konferensbidrag (refereegranskat)abstract
- Memories may integrate elements experienced in different events. For instance, meeting a woman leaving her house, and later meeting another woman entering the same house, may allow us to infer that the two women live together. Such memory representations are thought to rely on integrative encoding mechanisms, allowing us to make inferences about the world and generalize knowledge to entirely new situations. This study uses multivariate pattern analysis (MVPA) of electrophysiological data to elucidate the temporal dynamics of integrative encoding. We adapted the associative inference task to investigate cross- episode memory integration. Participants first learned overlapping paired associates, AB and CB pairs, that comprised a word and a picture (a face or a bird). Memory was later tested for the AC inferred associations, and for the direct AB and CB associations. MVPA was used to measure the online reactivation of previously learnt AB memories during encoding of the CB events. Reliable reactivation of AB was observed between 1.5 and 3 s. Participants (n=29) were divided into subgroups according to their AC performance: good and poor generalizers. Interestingly, while both groups showed comparable levels of AB reactivation during CB learning, the reactivation effects were associated with different consequences. For good generalizers, reactivation was predictive of later AC inference performance, suggesting that an integrated ABC representation was formed during BC learning. This interpretation is corroborated by behavioral data showing that direct and indirect inferred associations were retrieved equally fast. Altogether, this suggests that AC inference in this group of participants was based on integrative encoding mechanisms. Conversely, for poor generalizers, the reactivation of AB was instead negatively correlated with BC retrieval performance, indicating that AB reactivation impaired BC learning. Additionally, this group of participants took longer to retrieve inferred associations than direct associations, suggesting that successful AC inference was accomplished by flexibly recombining the direct AB and CB associations during retrieval. The present study extends previous literature by revealing the temporal dynamics of memory integration and providing an account of inter-individual differences in the capacity to make inferences across distinct episodes.
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| 20. |
- Nikolaev, Andrey, et al.
(författare)
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Episodic memory formation in unrestricted viewing
- 2023
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Ingår i: NeuroImage. - : Elsevier BV. - 1095-9572 .- 1053-8119. ; 266
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Tidskriftsartikel (refereegranskat)abstract
- The brain systems of episodic memory and oculomotor control are tightly linked, suggesting a crucial role of eye movements in memory. But little is known about the neural mechanisms of memory formation across eye movements in unrestricted viewing behavior. Here, we leverage simultaneous eye tracking and EEG recording to examine episodic memory formation in free viewing. Participants memorized multi-element events while their EEG and eye movements were concurrently recorded. Each event comprised elements from three categories (face, object, place), with two exemplars from each category, in different locations on the screen. A subsequent associative memory test assessed participants’ memory for the between-category associations that specified each event. We used a deconvolution approach to overcome the problem of overlapping EEG responses to sequential saccades in free viewing. Brain activity was time-locked to the fixation onsets, and we examined EEG power in the theta and alpha frequency bands, the putative oscillatory correlates of episodic encoding mechanisms. Three modulations of fixation-related EEG predicted high subsequent memory performance: 1) theta increase at fixations after between-category gaze transitions, 2) theta and alpha increase at fixations after within-element gaze transitions, 3) alpha decrease at fixations after between-exemplar gaze transitions. Thus, event encoding with unrestricted viewing behavior was characterized by three neural mechanisms, manifested in fixation-locked theta and alpha EEG activity that rapidly turned on and off during the unfolding eye movement sequences. These three distinct neural mechanisms may be the essential building blocks that subserve the buildup of coherent episodic memories during unrestricted viewing behavior.
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| 21. |
- Nikolaev, Andrey, et al.
(författare)
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Neural correlates of episodic memory buildup in naturalistic viewing behavior
- 2021
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Konferensbidrag (refereegranskat)abstract
- In everyday life, we bind visual samples of the world into a coherent episodic memory via eye movements. Previous eye tracking research revealed that visual scrutiny, gaze transitions between event elements, and refixations during encoding predict successful memory formation. However, little is known about the neural mechanisms of these processes. Here, we combine EEG and eye tracking to investigate the buildup of episodic memory representations in naturalistic viewing behavior.Twenty-eight participants encoded a series of events. Each event consisted of elements from three categories (faces, places, objects) and was presented for 10 s. After a distractor task, memory was tested for all event-specific element combinations. To succeed in the test, participants had to separate the different events by making strong associations between within-event elements. The simultaneously recorded EEG and eye movements were analyzed at the encoding stage of the task.A major problem of EEG-eye movement coregistration in free viewing concerns the overlapping effects of sequential saccades on EEG. We overcame this by using the regression-based deconvolution method, which allows correction of such overlap as well as removal of the confounding effects from eye movement characteristics and ordering factors, such as fixation rank. After deconvolution, we extracted EEG theta and alpha activity in epochs from -200 to +400 ms relative to the fixation onset.As expected, subsequent memory performance for the whole event increased with the cumulative number of fixations within single elements and inter-category gaze transitions between elements. We found that these two gaze memory effects are associated with two distinct memory effects of the fixation-related EEG activity: theta synchronization over the frontal and centro-parietal areas, respectively. The frontal theta effect may indicate the sampling of individual elements, whereas the centro-parietal theta effect may reflect the binding of elements into a coherent episodic event. Furthermore, memory performance was predicted by gaze returns to already visited categories. This refixation effect was associated with a fixation-related alpha desynchronization over the occipital areas. This may indicate the pivotal role of refixations in temporal accumulation of visual information that is needed for building a coherent representation of the whole event.We conclude that the combination of theta synchronization and alpha desynchronization at the fixation level supports the buildup of a coherent episodic memory across sequential eye movements.
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| 22. |
- Nikolaev, Andrey, et al.
(författare)
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Switching between neural modes at sequential fixations in free viewing predicts successful episodic memory
- 2022
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Konferensbidrag (refereegranskat)abstract
- ObjectivesThe formation of episodic memories is critically determined by how we visually sample the world over time via sequences of eye movements. Nonetheless, in the neuroscience of human memory, memory encoding has almost exclusively been studied in experimental paradigms where the study material is presented in a single fixed location on the screen, and where eye movements are treated as artifacts. Thus, the neural mechanisms subserving memory construction across eye movements are virtually unknown.Research questionWhat are the neural correlates of episodic memory formation during eye movements in natural visual behavior?Materials and methodsWe developed an associative memory task in which participants encoded multiple events, each comprising distinct elements from three categories (faces, places, objects) in different locations of the screen. The spatial configuration of the element locations allowed us to separate relevant and irrelevant saccades for integrating them into a coherent event. Participants memorized the event, while their EEG and eye movements were simultaneously recorded. Episodic memory was thereafter assessed by testing retrieval of the element associations specifying each event. In the EEG analysis, we overcame the problem of overlapping EEG responses to sequential saccades in free viewing using a deconvolution approach. We segmented EEG relative to the fixation onset and examined the power of EEG signals in the theta and alpha frequency bands.ResultsHigh subsequent memory performance was predicted by theta synchronization over the centro-parietal areas during fixation intervals after saccades relevant to event integration. This may reflect the binding of elements into coherent event representation. High memory performance was also predicted by alpha desynchronization during fixations after task-irrelevant saccades. This may reflect discrimination of elements from the same category, which is necessary for successful memory encoding. Finally, high frontal theta power during fixations after scrutinizing, within-element saccades predicted high memory. This may reflect increased visual sampling of elements leading to better memory.ConclusionThus, memory formation across eye movements is characterized by three neural mechanisms that rapidly turned on and off in a saccadic sequence during event encoding. These mechanisms provide essential building blocks for the construction of episodic memory during naturalistic viewing.
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| 23. |
- Nikolaev, Andrey, et al.
(författare)
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Watching the brain build memories across eye movements: an EEG - eye-tracking coregistration study
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Introduction Episodic memory allows us to revisit our past and recollect inter-related elements that characterize life events (Tulving, 1983). When forming such relational memories, we only apprehend a small part of our visual field in full acuity at a time. This limitation is overcome by shifting visual attention over a sequence of eye movements. We bind these visual “samples” of the world into a coherent episodic memory. However, little is known about how we build coherent episodic memories across eye movements. Previous studies have established crucial roles of theta and alpha oscillations in memory formation (Hanslmayr et al. 2012; Herweg et al., 2020), but lacked the necessary precision to elucidate how coherent representations are formed over time across eye movements. Here, we combine EEG and eye-tracking to investigate the buildup of episodic memory representations in natural viewing behavior. Methods Participants (N = 28) were asked to encode events with elements from three categories (faces, places, objects, Fig. 1). In each block (N = 6), nine events were presented for 10 s each. After a distractor task, memory was tested for all event-specific combinations of elements. EEG and eye movements were simultaneously recorded. Only data from the encoding phase was analyzed. A major problem in coregistration of EEG and eye movements in free viewing concerns overlapping effects of sequential saccades on EEG (Dimigen et al., 2011; Nikolaev et al., 2016). In order to overcome this, we used the deconvolution approach (Ehinger & Dimigen 2019). This regression-based method involves modelling not only experimental conditions of interest but also confounding eye movement characteristics and ordering factors, such as fixation rank, which can be “regressed out”. Before deconvolution, EEG was filtered in the theta and alpha frequency bands. The theta and alpha power were analyzed in epochs from -200 ms to +500 ms relative to the fixation onset. Results During the 10 s encoding, participants made, on average, 5.1 gaze transitions between categories. Subsequent memory performance increased with the cumulative number of gaze transitions during encoding (p < 0.001). Theta power in the interval -100+300 ms relative to the fixation onset over the frontal channels increased with time (p = 0.03) and performance (p = 0.02) (Fig. 2). Conversely, alpha power in the interval -100+300 ms over all electrodes prominently decreased with time (p = 0.002), irrespective of memory performance (Fig. 2). Next, we compared EEG for the first fixation on a category (i.e., after an inter-category saccade) with the last fixation on that category (i.e., after an intra-category saccade). The theta power in the interval -100+300 ms was significantly higher for the first than the last fixation (p < 0.001) and was more prominent for high than low memory performance (p < 0.001) (Fig. 1). The alpha power in the interval 0+500 ms was lower for the last than for the first fixation (p < 0.001), and lower for high than low memory performance at the last fixation (p = 0.02). Conclusions The frontal theta increase over the time of the event and for successful retrieval support the proposed pivotal role of theta synchronization in the formation of episodic memories (Clouter et al. 2017) and extends it to the binding of event elements across eye movements. The prominent theta effects in the interval of saccade execution and the larger theta power for fixations after inter- than intra-category saccades suggest that binding occurs via association of pre- and post-saccadic information at gaze transitions between categories. Alpha desynchronization over the time course of encoding may reflect an increasing amount of information (Hanslmayr et al. 2016) that is captured at each sequential fixation. The larger desynchronization associated with higher performance for fixations after intra- than inter-category saccades indicates active engagement of cortical areas in information acquisition during encoding.
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