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Vision and Action: Electrophysiological Recordings
Book - Dissertation
Functional modularity in human visual processing was already described 30 years ago, with a ventral 'vision for recognition' stream and a dorsal 'vision for action' stream. At the same time, however, the neural basis of human vision and its relation to the motor system remains largely unexplained.Using a novel multi-electrode microdrive, we were able to simultaneously record from a large number of frontal brain areas in the non-human primate during a saccade-reach-grasp task. We could demonstrate the neural dynamics in frontal cortex during visuomotor transformations, a sequence of activations that reflects visual to motor coding. We observed an unexpected sustained raise in activity of pre-arcuate neurons after the saccade. We hypothesize that this sustained visual activity is causally related to object grasping, and therefore most likely relevant for eye-hand coordination.In three subsequent studies in the ventral stream, we first describe a patient with a unilateral lesion to the lateral occipital complex (LOC) and underlying white matter tracts who experienced transient visual hemi-agnosia, confirming a causal link between occipitotemporal structures and object recognition in humans.Using microelectrode recordings in occipitotemporal cortex, we were able to study the human ventral visual stream at the highest spatiotemporal resolution. Contrary to predictions derived from functional imaging studies, the neuronal properties indicated that the posterior subsector of LOC occupies an unexpectedly high position in the hierarchy of visual areas. Responses of LOC neurons were relatively late, shape selectivity was spatially clustered, receptive fields were large and bilateral, and a number of LOC neurons exhibited 3D-structure selectivity, all properties of end-stage ventral visual stream areas.We found face-selective neurons in human occipitotemporal cortex. These neurons did not only react to intact faces, but also to objects with face-like features. Our findings confirmed that these neurons act as face-detectors, and represent an early stage in the face-processing network.These studies contribute to the understanding of the neural mechanisms of the visual system and its relation to the motor system.