Mémoire sémantique | EPFL Graph Search

En psychologie cognitive, la mémoire sémantique est le système mnésique par lequel l'individu stocke ses connaissances générales : connaissances actuelles sur le monde, définitions de concepts abstraits La mémoire sémantique est un type de mémoire déclarative. En 1972, Endel Tulving propose de distinguer la mémoire épisodique et la mémoire sémantique comme deux composantes de la mémoire déclarative. La mémoire sémantique constitue une base de connaissances, un magasin d'informations que nous possédons tous et dont une grande partie nous est accessible rapidement et sans effort. Selon Tulving en 1972, c’est la mémoire nécessaire à l’utilisation du langage, c’est un thésaurus mental, le savoir organisé qu’un individu possède pour les mots, les symboles non verbaux et leurs significations. La mémoire sémantique n’enregistre pas les propriétés des stimuli mais plutôt les référents cognitifs des signaux d’entrée. La mémoire sémantique, préservée dans le syndrome amnésique, constitue

Hippocampal Contribution to Ordinal Psychological Time in the Human Brain

Baptiste Gauthier

The chronology of events in time-space is naturally available to the senses, and the spatial and temporal dimensions of events entangle in episodic memory when navigating the real world. The mapping of time-space during navigation in both animals and humans implicates the hippocampal formation. Yet, one arguably unique human trait is the capacity to imagine mental chronologies that have not been experienced but may involve real events-the foundation of causal reasoning. Herein, we asked whether the hippocampal formation is involved in mental navigation in time (and space), which requires internal manipulations of events in time and space from an egocentric perspective. To address this question, we reanalyzed a magnetoencephalography data set collected while participants self-projected in time or in space and ordered historical events as occurring before/after or west/east of the mental self [Gauthier, B., Pestke, K., & van Wassenhove, V. Building the arrow of time horizontal ellipsis Over time: A sequence of brain activity mapping imagined events in time and space.Cerebral Cortex,29, 4398-4414, 2019]. Because of the limitations of source reconstruction algorithms in the previous study, the implication of hippocampus proper could not be explored. Here, we used a source reconstruction method accounting explicitly for the hippocampal volume to characterize the involvement of deep structures belonging to the hippocampal formation (bilateral hippocampi [hippocampi proper], entorhinal cortices, and parahippocampal cortex). We found selective involvement of the medial temporal lobes (MTLs) with a notable lateralization of the main effects: Whereas temporal ordinality engaged mostly the left MTL, spatial ordinality engaged mostly the right MTL. We discuss the possibility of a top-down control of activity in the human hippocampal formation during mental time (and space) travels.

MIT PRESS2020

Building the Arrow of Time ... Over Time: A Sequence of Brain Activity Mapping Imagined Events in Time and Space

Baptiste Gauthier

When moving, the spatiotemporal unfolding of events is bound to our physical trajectory, and time and space become entangled in episodic memory. When imagining past or future events, or being in different geographical locations, the temporal and spatial dimensions of mental events can be independently accessed and manipulated. Using time-resolved neuroimaging, we characterized brain activity while participants ordered historical events from different mental perspectives in time (e.g., when imagining being 9 years in the future) or in space (e.g., when imagining being in Cayenne). We describe 2 neural signatures of temporal ordinality: an early brain response distinguishing whether participants were mentally in the past, the present or the future (self-projection in time), and a graded activity at event retrieval, indexing the mental distance between the representation of the self in time and the event. Neural signatures of ordinality and symbolic distances in time were distinct from those observed in the homologous spatial task: activity indicating spatial order and distances overlapped in latency in distinct brain regions. We interpret our findings as evidence that the conscious representation of time and space share algorithms (egocentric mapping, distance, and ordinality computations) but different implementations with a distinctive status for the psychological "time arrow."

OXFORD UNIV PRESS INC2019

VIODE: A Simulated Dataset to Address the Challenges of Visual-Inertial Odometry in Dynamic Environments

Dario Floreano, Koji Minoda, Fabian Maximilian Schilling, Valentin Wüest

Dynamic environments such as urban areas are still challenging for popular visual-inertial odometry (VIO) algorithms. Existing datasets typically fail to capture the dynamic nature of these environments, therefore making it difficult to quantitatively evaluate the robustness of existing VIO methods. To address this issue, we propose three contributions: firstly, we provide the VIODE benchmark, a novel dataset recorded from a simulated UAV that navigates in challenging dynamic environments. The unique feature of the VIODE dataset is the systematic introduction of moving objects into the scenes. It includes three environments, each of which is available in four dynamic levels that progressively add moving objects. The dataset contains synchronized stereo images and IMU data, as well as ground-truth trajectories and instance segmentation masks. Secondly, we compare state-of-the-art VIO algorithms on the VIODE dataset and show that they display substantial performance degradation in highly dynamic scenes. Thirdly, we propose a simple extension for visual localization algorithms that relies on semantic information. Our results show that scene semantics are an effective way to mitigate the adverse effects of dynamic objects on VIO algorithms. Finally, we make the VIODE dataset publicly available at https://github.com/kminoda/VIODE.

2021

Hippocampal Contribution to Ordinal Psychological Time in the Human Brain

Baptiste Gauthier

MIT PRESS2020