It is established that there are different parallel loops, which consist of the extrastriate merely cortices (cortical regions surrounding the suprasylvian sulcus in the feline brain, the middle temporal area (MT), the medial superior temporal area (MST), the superior temporal polysensory area (STP) in the primate brain) and subcortical structures (pretectum, accessory optic system, basal ganglia, thalamus). According to the classical theory, these extrastriate structures play subservient and complementary roles in motion sensation. The two-stage motion processing theory is a generally accepted hypothesis [13�C16]. It assumes that at the first stage the analysis of the object features as one-dimensional components occurs in early visual areas, depending on orientation-selective Inhibitors,Modulators,Libraries mechanisms sensitive to the motion of individual component contours.
The second stage elements are regarded as pattern motion detectors, and these are possibly higher extrastriate cortical areas integrating the output of the first Inhibitors,Modulators,Libraries stage analyzers to construct the actual direction of the coherent pattern. However, more and more evidence is found to raise the suspicion that the two-stage theory might be incomplete for modeling the visual motion analysis [10,11,17]. Rather, the extrastriate structures have equal and coordinate functions in receiving direct input from the lower, primary stages of the visual stream, not only through indirect connections from the primary visual cortical areas.The aim of the present review is to give a detailed description of the extrastriate visual structures of the feline and the macaque brain and discuss their functional role in visual motion perception.
Special attention was paid in the second part of this review to the ascending tectofugal system in the feline brain that may serve the perception Inhibitors,Modulators,Libraries of self-motion.2.?Retino-Geniculo-Cortical Visual Pathways in PrimatesIn the visual pathways of vertebrates, motion perception spreads from retinal cells to higher cortical areas Inhibitors,Modulators,Libraries (Figure 1).Figure 1.Schematic representation of the primate visual pathways. The left half of the figure represents the ventral (��what��) stream, while the right side shows the hierarchical organization of the dorsal (��where��) stream. Abbreviations: …The first stage is the retina, comprising of three functional layers: rods and cones, bipolar cells, and ganglion cells.
The horizontal cells between rods and cones and the Batimastat amacrine cells between ganglion cells establish lateral connections. Morphologically, 10 layers may be distinguished, the description of which, however, we set aside as being outside the scope of the present study. The first integrative stage in the processing of an image is the layer of ganglion sellckchem cells. To our present knowledge, Three major types of ganglion cells might be distinguished, although at least 17 types are known altogether .