Perception from Sensation to Representation
Working of Our Visual System
Perception – The prerequisite for vision is the presence of light. Light is electro-magnetic radiation that can be defined in terms of wavelength. Humans can perceive only a slight range of the wavelengths that exist; the evident wavelengths are from 380 to 750 nanometers. Vision commences when light passes through the protective covering of the eye. This cover, the
- Cornea, is a clear dome that protects the eye. The light then passes over the Pupil, the opening in the center of the It carries on through the crystalline lens and the vitreous humor.
- The Vitreous humor is a gel-like element that comprises the majority of the eye. Ultimately, the light focuses on the retina where electromagnetic light energy is transduced that is, converted into neural electrochemical impulses. Vision is best acute in the fovea,
- Fovea that is a small, thin region of the retina, the size of the head of a pin. When you stare conventional at an object, your eyes rotate so that the image falls directly onto the fovea. Even though the retina is only about as thick as a single page in this book, it involves three main layers of neuronal tissue. The primary layer of neuronal tissue closest to the front, outward-facing surface of the eye is the layer of ganglion cells, whose axons constitute the optic nerve. The another layer consists of three kinds of interneuron cells. Amacrine cells and horizontal cells. The retina is made up of rods and cones, horizontal cells, amacrine cells, bipolar cells and ganglion cells. Make single lateral associates among adjacent areas of the retina in the middle layer of cells. Bipolar cells usually create dual links which are forward and outward to the ganglion cells, in addition with backward and inward to the third layer of retinal cells. The third layer of the retina holds the photoreceptors, which convert light energy into electrochemical energy that is transferred by neurons to the brain. There are two classifications of photoreceptors which are rods and cones. Individually eye contains roughly 120 million rods and 8 million cones. Rods and cones vary not only in shape but also in their arrangements, locations, and responses to light. Within the rods and cones are
- Photopigments, chemical materials that respond to light and transform physical electromagnetic energy into an electrochemical neural impulse that can be understood by the brain. The rods are long and thin photoreceptors. They are more highly concentrated in the edge of the retina than in the foveal region. The rods are responsible for night vision and are sensitive to light and dark stimuli. also in their configurations, locations, and responses to light. Within the rods and cones are photopigments, chemical substances that react to light and transform physical electromagnetic energy into an electrochemical neural impulse that can be understood by the brain. The rods are long and thin photoreceptors. They are more highly concentrated in the periphery of the retina than in the foveal region. The rods are responsible for night vision and are sensitive to light and dark stimuli.
The rods, cones, and photopigments might not do their work were they not someway hooked up to the brain. The neurochemical messages managed by the rods and cones of the retina travel by means of the bipolar cells to the ganglion cells. The axons of the ganglion cells in the eye collectively form the optic nerve for that eye. The optic nerves of the both eyes joint at the base of the brain to form the optic chiasma. At this point, the ganglion cells from the inward, or nasal, part of the retina the part closer to your nose cross over the optic chiasma and encompass to the opposite hemisphere of the brain. The ganglion cells from the outward, or temporal area of the retina closer to your temple go to the hemisphere on the same side of the body. The lens of each eye naturally inverts the image of the world as it projects the image onto the retina. In this way,
the message sent to your brain is literally upside-down and backward. After being routed via the optic chiasma, about 90% of the ganglion cells then go to the lateral geniculate nucleus of the thalamus.
- From the Thalamus, neurons carry information to the primary visual cortex in the occipital lobe of the brain.
- The Visual Cortex contains several processing areas. Each area handles different kinds of visual information relating to intensity and quality, plus color, location, depth, pattern, and form.