Overt Visual Attention as a Causal Factor of Perceptual Awareness

Our everyday conscious experience of the visual world is fundamentally shaped by the interaction of overt visual attention and object awareness. Although the principal impact of both components is undisputed, it is still unclear how they interact. Here we recorded eye-movements preceding and following conscious object recognition, collected during the free inspection of ambiguous and corresponding unambiguous stimuli. Using this paradigm, we demonstrate that fixations recorded prior to object awareness predict the later recognized object identity, and that subjects accumulate more evidence that is consistent with their later percept than for the alternative. The timing of reached awareness was verified by a reaction-time based correction method and also based on changes in pupil dilation. Control experiments, in which we manipulated the initial locus of visual attention, confirm a causal influence of overt attention on the subsequent result of object perception. The current study thus demonstrates that distinct patterns of overt attentional selection precede object awareness and thereby directly builds on recent electrophysiological findings suggesting two distinct neuronal mechanisms underlying the two phenomena. Our results emphasize the crucial importance of overt visual attention in the formation of our conscious experience of the visual world

Sensory tuning in neuronal movement commands

Successful interaction with our environment requires constant sampling of new sensory information by our brain. In vision, sampling is achieved by means of orienting eye movements, which entail both receiving visual input as well as generating movement commands. Indeed, oculomotor structures like the midbrain superior colliculus (SC) contribute to both processes. Conventionally, however, SC visuo-motor integration is believed to occur in a sequential manner: “vision” first takes place, and “action” follows. Thus, if the same saccade is made towards two different image features, the SC motor bursts should be completely the same; it should not matter, from a motor perspective, whether the saccade target is a car or a face. Here, by recording from SC neurons while monkeys generated saccades towards peripheral stimuli of varying visual features, we found intriguing evidence to the contrary. SC movement commands exhibit robust sensory tuning that is not explained by systematic changes in saccade properties; for a given saccade, the SC motor burst could be strong or weak simply as a function of the image features at the saccade target location. This sensory tuning of SC neural movement commands can afford higher brain areas with information about the upcoming foveated visual stimulus, which can aid in establishing perceptual stability in the face of saccade-induced retinal image shifts. To explore this possibility, we measured human peri-saccadic perceptual thresholds when saccades were made to different image features. As expected, participants exhibited elevated thresholds around saccades. Critically, however, the thresholds varied significantly with the saccade targets’ image features. These results provide a novel insight on the functional role of SC motor bursts, and they suggest that corollary discharge of SC neural movement commands can extend beyond simple spatial location updating to relaying information about the visual properties of saccade targets

Antibacterial and in vivo reactivity of bioactive glass and poly(vinyl alcohol) composites prepared by melting and sol-gel techniques

International audienceBioactive glass particle is used in the repair of bone defects. This material undergoes a series of surface in vivo reactions, which leads to osteointegration. We evaluated the effect of the bioactive glass synthesis, sol-gel (BG(S)) versus melting (BG(M)), associated with polyvinyl-alcohol (PVA) on in vivo bioactivity with biochemical parameters, liver-kidney histological structure and antibacterial in vitro activity. These composites were testified in many bacteria and implanted in ovariectomized rat. The serum and organs (liver and kidney) of all groups, control and treated rats, were collected to investigate the side effects of our composites, BG(S)-PVA and BG(M)-PVA, in comparison with control and ovariectomized rats. Also, the implants, before and after implantation, were prepared for analysis using physicochemical techniques such as Fourier transform infrared spectroscopy and X-ray diffraction. Our results have shown the stability of natremia, kaliemia, calcemia and phosphoremia. The histological structures of liver and kidney in implanted rats are intact compared to control and ovariectomized rats. BG(S)-PVA is characterized by a higher antibacterial effect on negative and positive gram bacteria than BG(M)-PVA. The physicochemical results have confirmed a progressive degradation of BG(S)-PVA and BG(M)-PVA, while replacing the implant by an apatite layer. But this bioactivity of BG(S)-PVA is faster than BG(M)-PVA. We can therefore confirm, on the one hand, the biocompatibility of our two implants and, on the other hand, the beneficial effect of sol-gel synthesis technique versus melting, both on the antibacterial effect and on the rapid formation of layer hydroxyapatite, and consequently on osteogenesi