Stable perception of external stimuli over time: oculo-motor and visual processing mechanisms

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When the animals populating the floor of the ocean started moving 600 million years ago, they faced an important evolutionary challenge: on one hand self-motion carry clear advantages: for example, finding new sources of food and escaping predators. On the other hand, it introduces ambiguity about the source of a sensory input. When you are crossing the street, you need to differentiate whether a motion is caused by a movement of a car (that need to be avoided), or a passive movement caused by you crossing the street (which can be ignored).Any animal that failed to correctly recognize the source of a sensory stimulation would have faced an evolutionary disadvantage, with devastating consequences.The species that successfully solved this problem did so by keeping track of their movement commands and informing the sensory system about forthcoming movements. Eye movements are a paradigmatic example of a specific sensory change, induced by the motor system. If we were to perceive the world exactly as it is displayed if front of our eyes, the visual scene would seem a sequence of frequent and large jumps, making any matching attempts between them impossible. It is crucial for the visual system to be able to distinguish 'jumps' that are due to saccades as opposed to changes in the external world. It is believed that the motor system provides the sensory system with a warning of an upcoming movement, to which the central nervous system responds with a compensatory mechanism.Evidence from monkey neurophysiology shows that several brain locations are particularly involved in the interaction between the oculo-motor system and vision, namely: the frontal and supplementary eye fields in monkey frontal cortex, several portions of the parietal cortex and motion sensitive areas.We have a general understanding of the fine organizational principles of these areas in monkey neocortex, but the same principles have not been tested in homologue areas of human cortex, so far.This reflects limitations intrinsic to standard human neuroimaging techniques. The spatial resolution in standard human neuroimaging studies is too coarse to characterize the detailed spatial organization typically observed in monkey neurophysiology. Ultra-high field imaging (7Tesla) helps overcoming these technical limitations, providing better and more detailed signal than standard neuroimaging acquisition. These advantages allow for a more detailed investigation that is not possible to image at lower fields (1.5 and 3Tesla), opening the possibility to test in humans, in vivo, the fine oculomotor-processing principles described in monkey neurophysiology.