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Co-organization of speed and direction in V1| old_uid | 18564 |
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| title | Co-organization of speed and direction in V1 |
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| start_date | 2020/12/01 |
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| schedule | 14h30-16h30 |
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| online | no |
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| details | En ligne. Inscription obligatoire au lien https://listsem.ehess.fr/ |
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| summary | It is classically admitted that only basic and static elements of the visual scene are encoded in primary visual areas, while coding of higher-level information like movement or shape of objects are processed downstream. We will report here new data and models revealing that in fact, movement velocity has an impact in the responses of neurons in early visual cortex of higher mammals. To characterize a potential encoding of movement in cat V1, we collected an extensive dataset of responses of primary visual cortex to stimuli with various orientations, directions, spatial frequencies and temporal frequencies, providing unprecedented opportunity to decipher the inter-relationship between the representation of these visual attributes. We observed no selectivity to motion in V1 cells responses. However, contrasting with classical coding paradigms, we found that motion significantly alters direction preference. This allows showing that visual maps are sensitive to speed of the stimulus (rather than temporal frequency), and that the modification of the direction map arises continuously by a smooth movement of the direction fractures. Using a machine learning algorithm, we show that the speed of a stimulus can indeed be retrieved from the activity maps in V1 only with high accuracy, and that a trade-off in the coding of speed vs direction happens, whereby speed is best coded at preferred direction where decoding of direction is weakest. This demonstrates that motion is accurately encoded at the level of primary visual areas, therefore potentially available to any downstream area, and that this information is encoded through a new modality involving modifications of the representations of another attribute. These findings thus shed a new light on visual perception in the primary visual areas, and lift the veil from a novel encoding mechanism. |
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| responsibles | Sarti, Petitot, Nadal |
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