photoreception

=Photoreception=

toc Read here about a receptor and details about its receptive capabilities across scales.

=Overview=

Sight or vision is the ability of the eye(s) to focus and detect images of visible light on photoreceptors in the retina.

=Rods and Cones in Humans=

There are two types of photoreceptors: rods and cones. Rods are very sensitive to light, but do not distinguish colors. Cones distinguish colors, but are less sensitive to dim light. There is some disagreement as to whether this constitutes one, two or three senses. Neuroanatomists generally regard it as two senses, given that different receptors are responsible for the perception of color and brightness. Some argue that stereopsis, the perception of depth using both eyes, also constitutes a sense, but it is generally regarded as a cognitive (that is, post-sensory) function of the visual cortex of the brain where patterns and objects in images are recognized and interpreted based on previously learned information. =Lack Of Vision= The inability to see is called blindness. =Vision= Optic nerves transmit from eye to brain outlines and clues about points of interest in our visual field. These aggregations, or “cortical memories” (Kurzweil p.157) are then accessible to conscious report. Werblin showed that the optic nerve carries ten to twelve output channels, each of which carries only minimal information about a given scene. (Kurzweil p.157 note 104). One group of what are called ganglion cells sends information only about edges (changes in contrast). Another group detects only large areas of uniform color, whereas a third group is sensitive only to the backgrounds behind figures of interest. Rods and cones resonate with inbound EM radiation, guided by the fluid lens to impinge on the retinal fabric. Cones are concentrated in the fovea. A cone cell is rooted in synaptic vescicles, its cell body (similar to a rod) rising to host a ste of stacked membranous disks containing rhodospin. A rod is thicker than a cone cell. The disks enable an ion channel in plasma membrane. The retina itself processes the vibrations and aggregated signaling is communicated to the brain. =Space And Vibration In Vision= In physiology, retinotopy (from Greek tono- and topos = place) is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighboring regions in the brain. Tonotopic maps are a particular case of topographic organization, similar to retinotopy in the visual system.