Visual Information Sensation and Perception



The retina of our eye is composed of two types of cells: cones and rods. Cones are nerve cells sensitive to light, detail, and color. Cones help us in reading letters and seeing objects, especially at center. Cones are packed into the macula and help in visual details. On the other hand, rods are helpful for night vision and detection of moving objects. Rods provide peripheral vision and are insensitive to color. Thus, when we go to a dark place from light, we are unable to see objects clearly. Their rods help us to distinguish objects, however, being insensitive to color, we are able to see only the colorless object. Figure 1: Log-polar mapping from the retina (left) to straight cortex (right). Points near the center of the visual field are represented more heavily in the cortex than are points in the periphery. Source: Schwartz (1994) Retina is the part of the eye which is composed of the layer of nerve tissue and it covers the back two-thirds of the eyeball. Retina receives the light and converts it into chemical energy which activates the nerves (cones and rods). These nerves conduct the messages out of the eye into the higher region of the brain. The retina thins out in the center of the macula forming a pit called fovea. The reason for its thinness is that the light passing through fovea is scattered or observed by this thinness before it reaches the photoreceptors. Several of these areas are retinotopic, that is, their neurons respond to stimulation of limited receptive fields whose centers are organized to form a continuous mapping between the cortical surface and the visual field. The boundaries between most of the low order visual areas can be determined from their retinotopic properties: the local representation of the visual field on the cortical surface changes its orientation-the local visual field sign (VFS)-between adjacent visual areas. &nbsp.Fovea Retina is located in the back of the eye and has a complex structure. It is composed of macula which lies in the center of the retina and the macula covers up to inch diameter. The macula further contains a very small area called fovea. The fovea is responsible for very sharp vision (20/20). The fovea has the highest concentration of cone photoreceptors, ganglion cells, and horizontal cells rather than the rods. The reason for the high concentration of cones is that cones function best in the bright light. That is why fovea works best in daylight illumination. On the other hand, rods function better in dim light and are not capable of sharp vision. Thus, naturally, there is a high concentration of cones in the fovea in order to make it capable of sharp vision (20/20). &nbsp.Comparison of Tactile with visual information&nbsp.&nbsp.Tactile Information: When we touch something, the nerves present in the skin are stimulated and carry this information to the brain where it is interpreted and processed. Thus, the tactile information comes from touching objects which are carried through the nerves ending in the skin that convey sensations to the brain via nerve fibers.&nbsp.