Two Visual System Hypothesis

The two visual systems hypothesis talks about the processing of the visual information in two different routes in the brain (van Polanen & Davare, 2015). This idea was first introduced in 1982 when Leslie Ungerleider and Mortimer Mishkin described experiments that distinguished two streams that served different functions(Melvyn A. Goodale, 1998). They used the method know as ablation or also called lesioning. Using both recordings from neurons and ablation, they found that properties of the ventral and dorsal streams are established by two different types of ganglion cells in the retina, which transmit signals to different layers of the LGN.(Goldstein, 2014). We know that information in the visual system progresses from the eye to the lateral
They said the position of the points in both normal and hallow were apparently the same. Then they were asked to flick the targets off using their fingers. Despite the presence of an illusion of a normal face, the flicking movements were rapid and directed at the real, not the illusory locations of the targets(M. A. Goodale, Kroliczak, Heard, & Gregory, 2010). These results show that the same visual stimulus can have completely opposite effects on conscious perception and visual control of fast action. This was contradicted by others, for example, Schroeder (1852), states that the illusion only works if the hollow shape resembles a familiar 3-D object. Gregory argues that it is the bias for seeing faces as convex that leads to the compelling impression of the familiar percept, a convex face with the nose pointing towards you (Hill & Johnston,
Aglioti demonstrated that the maximum opening of a grasping hand is insensitive to the perceptual illusion. The grip opening is sensitive to real changes in the size of the target disk. (Haffenden and Goodale, 1998). Although size-contrast illusions have a powerful effect on the perceptual judgments of an object's size, grasping movements directed at that same object remain metrically accurate. A similar experiment was conducted by Richard Dyde and David Milner (2002), known as rod and frame illusion, where the two small lines inside the tilted squares appear slightly tilted in opposite directions, while they actually are parallel vertical lines but this didn’t affect the grasping movement of the participants. These results support the idea that perception and action are served by different mechanisms(M. Goodale,