Soutenance de thèse de Kiana Mansour Pour

1er avril 2019

Salle Henri Gastaut, INT

Lundi 1er à 14h


Titre : effet de la variabilité de la vitesse sur le mouvement de poursuite oculaire lente et sur la perception de la vitesse

Jury :

  • Stéphane Violet, Président, ISM, CNRS, Marseille
  • Jean Lorenceau, Rapporteur, IDV, CNRS, Paris
  • Maria Concetta Morrone, Rapporteur, CNR, Université de Pise, Italie
  • Kenneth Knoblauch, Examinateur, ICSC, INSERM, Lyon
  • Guillaume Masson, Directeur, INT, CNRS, Marseille
  • Anna Montagnini, Directeur, INT, CNRS, Marseille
  • Laurent Perrinet, Directeur, INT, CNRS, Marseille

Abstract

It is still not fully understood how the visual system integrates motion information across different spatial and temporal frequencies, in order to build a coherent percept of the global motion under complex, noisy naturalistic conditions. We addressed this question by manipulating local speed distribution (i.e. speed bandwidth Bv) using a well-controlled class of broadband random-texture stimuli called Motion Clouds (MCs), with continuous naturalistic spatiotemporal frequency spectra (Sanz-Leon et al., 2012, ; Simoncini et al., 2012). In the first series of smooth pursuit experiments participants were asked to follow the global direction of motion. Our results show that pursuit gain and precision deteriorate as stimulus speed variability increases. In the second perceptual speed discrimination experiment, where participants had to compare the speed of two Motion Cloud (MC) of different speed bandwidth, we found that MCs with moderately larger speed bandwidth (between 0.05-0.5°/s) were perceived as moving faster. However, beyond a critical bandwidth (Bv > 0.5 °/s), the perception of a coherent speed was progressively lost. In a third direction discrimination experiment, participants had to estimate the motion direction of moving MCs with different speed bandwidths. We found that for large bandwidth MCs participants could no longer discriminate motion direction. These results suggest that when increasing speed bandwidth from a small to a large range, the observer experiences different perceptual regimes. We finally ran a Maximum Likelihood Difference Scaling (Knoblauch & Maloney, 2008) experiment with our MC stimuli to investigate these different possible perceptual regimes. We identified three regimes across the range of tested values of velocity difference, that would correspond to motion coherency (and speed integration), motion transparency and complete incoherency.

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