Séminaire du 10 novembre 2009

Claudio de'Sperati présentera "Low-threshold motor decisions"

• Intervenant : Claudio de'Sperati
• Laboratoire : Visuo-Motor Functions Lab, Universitá San Raffaele, Milan, Italy
• Date prévue : 10 novembre 2009 à 16h30
• Lieu : salle D28, 1er étage, bâtiment BSHM
• Titre : Low-threshold motor decisions
• Abstract :

  In the talk I will present two recent studies that illustrate the differential buildup of visuo-motor decisions and perceptual awareness after a stimulus has impinged on the retina.

  In the first study (de'Sperati & Baud-Bovy 2008) we examined an asynchrony between seeing and looking in a localization task, as revealed by blind saccades. We exploited a motion-induced visual illusion, in which the apparent position of a target is perceptually mislocalized in the direction of motion. We found that, whereas long-latency saccades reflected this illusion, short-latency saccades were accurately directed to the target. We reconstructed the time-course of the saccadic mislocalization, and identified a pre-preceptual (between ~50 and ~250 ms) and a perceptual (between ~250 and ~500 ms) component, indicating that saccades occurring during an early sensory-motor phase of cortical processing escape the tricks of perception (blind saccades). This transient dissociation between action and perception suggests that perceptual awareness is rather sluggish.

  In the second study (Gregori-Grgic, Balderi & de'Sperati) we addressed more directly in a trial-by-trial way the relation between visually-guided behaviour and perceptual awareness, and found an early dissociation that decays over time, and that underlies successful speeded decisions. By exploiting the long integration time of noisy motion stimuli, and by forcing observers to emit a speeded response, we showed that about half second after stimulus onset the capability of discriminating motion direction with a saccadic eye movement or a verbal response can be remarkably high despite poor or null perceptual awareness, which in fact required more time, and a stronger signal, to reach a steady-state, as assessed through a perceptual awareness scale.

  The findings from these two studies converge in indicating that consciousness is not a prerequisite for intuitive, rapid decisions, because a fleeting "low-threshold mode" ensures a good performance prior to the stabilization of perceptual awareness. As a consequence, several moment-to-moment decisions - e.g., where to look - can be taken pre-consciously based on early sensory signals, when the conscious representation starts unfolding in time.