Willpower and Conscious Percept: Volitional Switching in Binocular Rivalry

When dissimilar images are presented to the left and right eyes, awareness switches spontaneously between the two images, such that one of the images is suppressed from awareness while the other is perceptually dominant. For over 170 years, it has been accepted that even though the periods of dominance are subject to attentional processes, we have no inherent control over perceptual switching. Here, we revisit this issue in response to evidence that top-down attention can target perceptually suppressed ‘vision for action’ representations in the dorsal stream. We investigated volitional control over rivalry between apparent motion (AM), drifting (DM) and stationary (ST) grating pairs. Observers demonstrated a remarkable ability to generate intentional switches in the AM and D conditions, but not in the ST condition. Corresponding switches in the pursuit direction of optokinetic nystagmus verified this finding objectively. We showed it is unlikely that intentional perceptual switches were triggered by saccadic eye movements, because their frequency was reduced substantially in the volitional condition and did not change around the time of perceptual switches. Hence, we propose that synergy between dorsal and ventral stream representations provides the missing link in establishing volitional control over rivalrous conscious percepts

Principles of sensorimotor learning.

The exploits of Martina Navratilova and Roger Federer represent the pinnacle of motor learning. However, when considering the range and complexity of the processes that are involved in motor learning, even the mere mortals among us exhibit abilities that are impressive. We exercise these abilities when taking up new activities - whether it is snowboarding or ballroom dancing - but also engage in substantial motor learning on a daily basis as we adapt to changes in our environment, manipulate new objects and refine existing skills. Here we review recent research in human motor learning with an emphasis on the computational mechanisms that are involved

New constraints on the Pb and Nd isotopic evolution of NE Atlantic water masses

Time series of lead (Pb) and neodymium (Nd) isotope compositions were measured on three ferromanganese crusts recording the evolution of NE Atlantic water masses over the past 15 Ma. The crusts are distributed along a depth profile (∼700–4600 m) comprising the present-day depths of Mediterranean Outflow Water and North East Atlantic Deep Water. A pronounced increase of the 206Pb/204Pb in the two deeper crusts starting at ∼4 Ma and a decrease in 143Nd/144Nd in all three crusts took place between ∼6–4 Ma and the present. These patterns are similar to isotope time series in the western North Atlantic basin and are consistent with efficient mixing between the two basins. However, the changes occurred 1–3 Ma earlier in the eastern basin indicating that the northeastern Atlantic led the major change in Pb and Nd isotope composition, probably due to a direct supply of Labrador Seawater via a northern route. The Pb isotope evolution during the Pliocene-Pleistocene can generally be explained by mixing between two end-members corresponding to Mediterranean Outflow Water and North East Atlantic Deep Water, but external sources such as Saharan dust are likely to have played a role as well. The Pb isotope composition of the shallowest crust that grew within the present-day Mediterranean Outflow Water does not show significant Pb isotope changes indicating that it was controlled by the same Pb sources throughout the past 15 Ma

Finding the target as a reinforcer of saccadic amplitude variability in a visual search task.

International audienc

Attention spatiale et formation des trajectoires pour le système saccadique

International audienc

Influence of near threshold visual distractors on perceptual detection and reaching movements.

Providing evidence against a dissociation between conscious vision for perception and unconscious vision for action, recent studies have suggested that perceptual and motor decisions are based on a unique signal but distinct decisional thresholds. The aim of the present study was to provide a direct test of this assumption in a perceptual-motor dual task involving arm movements. In 300 trials, 10 participants performed speeded pointing movements toward a highly visible target located at 10° from the fixation point and ± 45° from the body midline. The target was preceded by one or two close to threshold distractor(s) (80 ms stimulus onset asynchrony) presented ± 30° according to the target location. After each pointing movement, participants judged whether the distractor was present or not on either side of the target. Results showed a robust reaction time facilitation effect and a deviation toward the distractor when the distractor was both present and consciously perceived (Hit). A small reaction time facilitation was also observed when two distractors were physically present but undetected (double-miss)--this facilitation being highly correlated with the physical contrast of the distractors. These results are compatible with the theory proposing that perceptual and motor decisions are based on a common signal but emerge from a contrast dependent fixed threshold for motor responses and a variable context dependent criterion for perceptual responses. This paper thus extends to arm movement control previous findings related to oculomotor control

Influence of near threshold visual distractors on perceptual detection and reaching movements.

Providing evidence against a dissociation between conscious vision for perception and unconscious vision for action, recent studies have suggested that perceptual and motor decisions are based on a unique signal but distinct decisional thresholds. The aim of the present study was to provide a direct test of this assumption in a perceptual-motor dual task involving arm movements. In 300 trials, 10 participants performed speeded pointing movements toward a highly visible target located at 10° from the fixation point and ± 45° from the body midline. The target was preceded by one or two close to threshold distractor(s) (80 ms stimulus onset asynchrony) presented ± 30° according to the target location. After each pointing movement, participants judged whether the distractor was present or not on either side of the target. Results showed a robust reaction time facilitation effect and a deviation toward the distractor when the distractor was both present and consciously perceived (Hit). A small reaction time facilitation was also observed when two distractors were physically present but undetected (double-miss)--this facilitation being highly correlated with the physical contrast of the distractors. These results are compatible with the theory proposing that perceptual and motor decisions are based on a common signal but emerge from a contrast dependent fixed threshold for motor responses and a variable context dependent criterion for perceptual responses. This paper thus extends to arm movement control previous findings related to oculomotor control