The Visual System From Eye to Cortex从眼睛到皮的视觉系统.pptVIP

The Visual System:From Eye to Cortex Ch. 6 Outline The Eye The Retina Visual Transduction by Rhodopsin From Retina to Primary Visual Cortex The Eyes Structure: review the major structures of the eye (diagram given in class) (note that the size of the pupils is a compromise between sensitivity and acuity) The Eyes ciliary muscles adjust the lenses to focus visual images sharply on each retina, regardless of the distance of the image from eyes; this focusing is called acommodation The Eyes When we look at something near, the ciliary muscles contract, tension on the lenses is reduced, and they become more cylindrical When we look at distant object, the muscles relax, tension on the lens is increased, and the lenses flatten The Eyes Binocular Disparity: unlike most vertebrates, most mammals have two eyes on the front of their heads, rather than one on each side; this cuts down the field of view, but it insures that most of what is seen is seen through both eyes The Eyes Because each eye sees things from a slightly different perspective, there is a difference in the two retinal images; this binocular disparity is greater for closer things; the degree of binocular disparity associated with a particular visual stimulus helps the brain create a 3-D perception from two 2-D retinal images thus depth perception is partially achieved from this (remember, we can still perceive depth with one eye closed) The Retina Structure: five layers receptor layer; horizontal cell layer; bipolar layer; amacrine cell layer; and retinal ganglion cell layer (diagram in class) The receptor is the farthest from light; therefore, incoming light is distorted by four layers of neurons before reaching the receptors The Retina The fovea is a pit about 330 micrometers in diameter; it is the only part of the retina capable of mediating high-acuity vision. This is due, in part, to the fact that axons of retinal ganglion cells are thinnest over the fovea and light is distorted less before reaching th