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Shaul Hochstein, Anna Barlasov, Orit Hershler, Adi Nitzan, Shneor Shneor; Rapid vision is holistic. Journal of Vision 2004;4(8):95. doi: 10.1167/4.8.95.
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Background: According to Reverse Hierarchy Theory (Ahissar & Hochstein, Nature, 1997; Hochstein & Ahissar, Neuron, 2002), rapid conscious vision reflects a high-level cortical representation. This permits implicit integration of multiple spatially separated stimulus elements and direct perception of complex forms on the basis of what must be called holistic properties. Methods and Results: We present three lines of evidence to support this hypothesis: 1- Pictures of faces, (whether line drawings or photographs), are rapidly detected within arrays of other disparate pictures (Hershler & Hochstein, VSS, 2002). This detection is based on holistic face properties, including either interior features or the exterior face contour, but multiple, scrambled features do not suffice. Other categories, for which we are less expert, are not perceived in the same holistic manner, and do not pop-out. For example, the degree of animal face pop-out is extremely variable across subjects. 2- Multiple odd elements may be detected as fast — or faster — than single odd elements (Hochstein & Shneor, VSS, 2003), and these elements may be integrated so that the shape of the inscribed form is easily discriminated (Sagi & Julesz, 1985). We find that such discrimination may depend on implicit representation of the precise location of particular elements, though explicit perception of location is much less precise. Thus, perception of the holistic form is more precise than that of its parts. 3- Perception of shapes described by illusory contours often depends on integration of numerous stimulus elements. Nevertheless, explicit perception of the shape described by these contours is rapid. Furthermore, subjects are able to “guess” the illusory shape even when they did not consciously perceive its parts. Again, the holistic percept is superior to that of the local elements upon which it depends. Conclusions: These results support the global and holistic nature of early perception, as suggested by Reverse Hierarchy Theory.
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