Where does vision begin? Competing with the mainstream view of "local to global", the topological approach emphasizes a "global-first" approach to perceptual organization by claiming that global topological invariants are extracted at the very beginning of visual processing. According to the levels of structural stability, a functional hierarchy in which the relative salience or priority in the perception of different geometric properties is remarkably consistent with the hierarchy of geometries (Euclidean, affine, projective and topological property) stratified by Klein's Erlangen Program. In the functional hierarchies, the topological property is the most stable and basic property that is the first to be extracted by the visual system to form basic constraints on object coding. However, it is still an unsolved question that how the topological perception is processed by the visual system. Some fMRI studies find the robust activation of anterior temporal lobe (ATL) responding to the topological perception. It seems like a contradiction that the beginning of visual perception is processed by the terminator of the typical visual pathway. In this paper, we aim to find out whether the topological perception is processed by the typical visual pathway or the other fast pathway. There is a phylogenetically older subcortical visual system including superior colliculus (SC), pulvinar and amygdala is found to process the less detailed but faster processing about emotion, bypassing the primary visual cortex. If topological perception is processed by this subcortical pathway, we suppose that emotion will interfere with topological perception. Our studies systematically and consistently demonstrated that fear emotion with or without conscious awareness both interrupted the topological perception, but not the perception of the other geometrical properties. The fMRI results further illustrated that amygdala actually took part in the topological perception processing.Hole is one of the basic topological properties. In the binocular rivalry study, we found that compared with no-hole, the hole property took less time to overcome the suppression induced by the dominate flash visual pattern and to be perceived with conscious awareness. Furthermore, we proceeded to apply Transcranial magnetic stimulation (TMS) on V1 to directly suppress the neural activation of V1, we found that the suppresstion did impair the performance of the discrimination of no-hole, but not hole. The results of TMS study provided a powerful demonstration to confirm that the hole perception could be processed indepent of the primary visual cortex. All the experiments consistently supported that the topological perception could be processed bypassing the primary visual cortex and maybe processed by the subcortical pathway. However, more experiments are needed to investigate it.
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