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Seeing and perceiving: phenomenology physiological mechanisms


Logothetis,  NK
Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Logothetis, N. (2004). Seeing and perceiving: phenomenology physiological mechanisms. Talk presented at 4th Forum of European Neuroscience (FENS 2004). Lisboa, Portugal.

Over the past ten years we recorded the activity of cells in the visual cortex of monkeys trained to report what they perceive when viewing perceptually rivalrous stimuli, which are known to instigate a continuous reorganization of perception. In any studied area only a fraction of neurons was found to respond in a manner that reliably reflects shifts in perception. This small number of neurons is distributed over the entire visual pathway, rather than being part of a single area in the brain. Of the areas we have studied the inferior temporal (IT) cortex of the temporal lobe was found to have the highest number of perception-related cells. Notably, a tight relationship between IT acitivity and the animal’s perception was clearly evident also in experiments in which monkeys were trained to look for and identify familiar targets embedded in natural scenes. During exploration, neuronal activation began shortly before effective targets were fixated, but only if the target was the goal of the next fixation. In my talk I’ll summarize these results and continue with the description of rivalry experiments in which both local field potentials and multiple unit activity were measured with multiple electrodes, placed over more than one visual areas. Of interest is the covariation of activity within and between various occipito-parietal areas under different stimulus and perceptual conditions. Significant coupling was found between distant sites both in non-stimulated and stimulated conditions. Stimulus-specific differences were subtle. During rivalry, covariation patterns were significantly diminished, and in some cases completely disappeared. Coherence in the response of visual neurons during rivalry may therefore be related to system’s stability rather than to the perceptual state of the animal. Finally, psychophysical experiments will be described examine the relation of the process of stabilization of ambiguous percepts with perceptual memory.