Speakers and abstracts

Aya Ben-Yakov - MRC Cognition and Brain Science Unit

  • Hippocampal encoding of naturalistic episodes is time-locked to the event offset - Hippocampal involvement in the encoding of new associations has been firmly established. However, most research has focused on encoding of discrete associations, whereas real life experiences contain a stream of information that unfolds over time. Using short film clips as memoranda, we find that when encoding naturalistic events, the hippocampus exhibits memory-predictive activity time-locked to the offset of the event. Moreover, when distinct clips are presented in immediate succession, the hippocampus responds at the offset of each event. I will discuss a potential interpretation of these findings, that automated hippocampal processes triggered by event boundaries (transition between events) serve to bind and register episodic events as cohesive units in long-term memory. The second part of the talk will focus on re-exposure to familiar events. As episodes become increasingly familiar through multiple repetitions, we find that the offset response is attenuated, in line with a novelty/encoding signal. In parallel, the hippocampus demonstrates an onset response which emerges only for familiar events, potentially reflecting a familiarity/retrieval signal. This provides the ability to dissociate encoding and familiarity signals elicited by the same event.

Chris Bird - University of Sussex

  • Interactions between episodic and semantic memory during naturalistic situations - There is remarkable overlap between three different networks that have been characterised in the human brain: the “semantic” network, the episodic “core retrieval” network and the “default” network. This is intriguing, given the varied tasks and procedures that have been used to identify these networks. Arguably, no event or object is processed by the brain without reference to existing knowledge. Thus, it is possible that semantic processing is the common cause of co-activations within these networks; when we are conscious, ongoing semantic processing is the default, whether recollecting the past, thinking about the future, engaging in the present or mindwandering. However, semantic processing occurs across a hierarchy of levels; for example, processing the relationships between items within a scene, linking an ongoing event with what has gone before and modifying existing representations on the basis of new information. Using video clips as stimuli, and manipulating the availability of prior knowledge, we are attempting to understand the individual contributions of different regions within these three networks to semantic processing at different levels of the hierarchy.

Richard Henson - MRC Cognition and Brain Science Unit

  • How expectation modulates memory of events - Sometimes events are better remembered when unexpected; other times, they are better remembered when they conform to expectations. I will describe 6 behavioural experiments that explore this apparent paradox. The first three experiments show that new associations between a scene and an object are better remembered the more strongly they violate predictions established by prior presentations of those scenes and/or objects. This supports the Predictive Interactive Multiple Memory Signals (PIMMS) framework, in which memory encoding is driven by prediction error, which reflects the divergence between two probability distributions: one reflecting the prior probability (from previous experiences) and the other reflecting the sensory evidence (from the current experience). The second set of experiments show that memory for a particular configuration of objects (event details, ie specific trial) is not only improved when the response associated with that configuration violates expectations (established from prior learning of a rule, or schema), consistent with PIMMS, but also when they conform to a stronger schema, provided the event details are relevant to the schema. In other words, there is a U-shaped function of memory performance against the degree of expectation, with best memory when events are highly congruent or incongruent with expectations, and worst memory when there is little expectation.

Aidan Horner - University of York

  • Event engrams do not (always) represent real-world events - Our ability to remember complex real-world events is thought to be supported by ‘event engrams’ – coherent representations of the constituent elements of any event that allow for later recollection. The hippocampus is thought to support these representations, receiving input from multiple neocortical regions to bind together the multiple elements of any event. However, recent research has suggested the hippocampus may also support the integration of related, but separately learnt, material. I will present work that supports the idea that ‘event engrams’ can be formed when information is separated in both space and time, when there is either shared content or context. First I will show that separately encoded overlapping pairwise associations (e.g., A-B, A-C, B-C) can form coherent representations that show behavioural and neural signatures similar to those seen for typical coherent spatiotemporal events5,6. Second, I will show that, controlling for spatial and temporal distance, objects that share spatial context (a room in virtual reality) are more readily associated than those that do not7. Thus, event engrams need not represent a single spatiotemporal event in the real world. More likely, they are formed (or altered) when there is predictive value in binding together related information, irrespective of whether it is experienced in the same time and place.

Beth Jefferies - University of York

  • Exploring the role of angular gyrus and posterior middle temporal gyrus in thematic and identity knowledge: A lesion approach - Event knowledge involves understanding the significance of objects and actions within a context. Some theories of semantic representation propose that an amodal store in the anterior temporal lobes (ATL) captures knowledge of both objects and events, while an alternative perspective proposes a “thematic hub” in temporoparietal cortex. In addition, the extraction and application of contextual information to support event understanding can require controlled retrieval, since meaning changes in different circumstances – for example, a flint tool can be used for scraping, cutting, or as an axe, depending on the circumstances. We found that the functional organisation of temporoparietal cortex reflects retrieval demands, not semantic content (e.g., relatively automatic retrieval in angular gyrus – AG; controlled retrieval in posterior middle temporal gyrus – pMTG). (i) A neuropsychological study found that semantic aphasia patients, with poor controlled retrieval, had difficulties retrieving weak but not strong associations. They also showed impaired identity-matching, irrespective of whether they had prefrontal or temporoparietal lesions. (ii) To increase the spatial specificity of our conclusions, we used TMS in healthy participants, targeting AG and pMTG. TMS to AG disrupted strong thematic judgements, while TMS to pMTG only disrupted weak thematic associations, in line with the controlled semantic cognition account. In addition, TMS to AG impaired the identification of objects at a specific level (e.g., Dalmatian), while TMS to pMTG produced greater disruption of superordinate identity matching. Our findings suggest that there is a functional dissociation within temporoparietal cortex, between AG and pMTG, but that neither of these sites is consistent with a thematic hub.

Ken McRae - University of Western Ontario
  • The importance of event knowledge in the organization and structure of semantic memory - People constantly use concepts and word meaning to recognize entities and objects in their environment, to anticipate how entities will behave and interact with one another, to know how objects should be used, and to understand language. Over the years, a number of theories have been presented regarding how concepts are organized and structured in semantic memory. For example, various theories stress that concepts (or lexical items) are linked by undifferentiated associations. Other theories stress hierarchical categorical (taxonomic) structure, whereas others focus on similarity among concepts. In this talk, I will present evidence that people’s knowledge of real-world events and situations is an important factor underlying the organization, structure, and (contextually-determined) usage of concepts in semantic memory. I will present experiments spanning word, picture, and sentence processing. Evidence for the importance of event-based knowledge will cover a number of types of concepts, including verbs, nouns denoting living and nonliving things, and abstract concepts. I conclude that semantic memory is structured in the mind so that the computation and use of knowledge of real-world events and situations is both rapid and fundamental.

Morris Moscovitch - University of Toronto

  • Interactions between hippocampus and neocortex during encoding and retrieval of natural events - Episodic memory for natural events depends on an interaction between perceptual and semantic information, and schemas. Using behavioural and fMRI methods, we tested memory for autobiographical events and for film clips at short and long delays in healthy controls and in patients with lesions to the medial temporal lobe or neocortex. We found that the quality of the memory was related to the contribution of these structures and their interactions, in particular those between the hippocampus and ventromedial prefrontal cortex.

Gabriella Vigliocco - University College London
  • Events, entities, verbs and nouns in the brain - In language, words referring to events are usually verbs and words referring to entities are nouns. Whereas it may be relatively uncontroversial that words referring to events and entities may recruit somewhat segregable neural networks in their processing, more controversial is whether such segregation is also present for grammatical class (here, nouns or verbs). I present a critical discussion of the behavioural, imaging and neuropsychological literature on processing words from different grammatical classes (and semantic domain) showing that once we take into account the confounding in most studies between semantic distinctions (objects vs. actions) and grammatical distinction (nouns vs. verbs), we account for task demands and, importantly, cross-linguistic differences, the emerging picture is relatively clear-cut: neural separability is observed between the processing of object words (nouns) and action words (typically verbs), grammatical class effects emerge or become stronger for tasks and languages imposing greater processing demands. These findings indicate that grammatical class per se is not an organisational principle of knowledge in the brain. Rather, these findings are compatible with two general principles described by typological linguistics as underlying grammatical class membership across languages: semantic/pragmatic, and distributional cues in language that distinguish nouns from verbs. 

Jon Simons
- University of Cambridge

  • Multimodal Feature integration during episodic and semantic retrieval - Remembering personally experienced events involves reactivating cognitive and perceptual event features and integrating them into a conscious representation during retrieval. The reactivation of distributed component features is also a defining characteristic of semantic retrieval, but with a very different phenomenological outcome. In this talk, I will consider evidence from patient lesion and brain stimulation studies, and from univariate and multivariate analyses of functional neuroimaging data, addressing the contribution of the lateral parietal lobe to the integration of distributed features during episodic and semantic retrieval. Our findings suggest that the angular gyrus region of the parietal lobe plays a key role during retrieval in integrating memory features from different modalities into an egocentric multisensory representation detailing how a past event played out. These processes enable the subjective first-person perspective re-experiencing of the event that is such a cardinal feature of episodic memory. In contrast, semantic retrieval engages angular gyrus to a similar degree regardless of task requirements to integrate features across modalities, consistent with proposals of more abstract, amodal context-independent semantic knowledge representations.

Jeffrey Zacks - Washington University in Saint Louis

  • Predicting, comprehending, and remembering events - In the laboratory, the “episodes” in episodic memory can be constructed from controlled materials such as list of words or pictures. In the real world, episodes must be constructed during encoding and that structure leaves its fingerprints on subsequent memory. In this talk I will describe a theory that relates the subjective experience of events to computational mechanisms of prediction error monitoring and memory updating. Briefly, Event Segmentation Theory proposes that perceivers maintain a working memory representation of the current event and use it to guide predictions about what will happen in the near future. When prediction error spikes, they update their model. Data from individual differences, neuropsychology, and neuroimaging suggest that this mechanism is functionally significant for memory and that it can be impaired by neurological injury or disease. New results indicate that it is possible to improve the encoding of event structure and that this may improve subsequent memory. Such results have implications for technology design and for the remediation of memory disorders in conditions including healthy aging, Alzheimer’s disease, and post-traumatic stress disorder.