Kafli 6 : Vision

Kafli 6 : Vision

1. Sensory receptor

   • A specialized neuron that detects a particular category of physical events.
   • Sensory Transduction
     • The process by which sensory stimuli are transduced into slow, graded receptr potentials.
   • Receptor Potential
     • A slow, graded electrical potential produced by a receptor to a physical stimulus.
   • Receptive Field
     • That portion of the visual field in which the presentation of visual stimuli will produce an alteration in the firing rate of a particular neuron.
     • Complex Cell
       • A neuron in the visual cortex that responds to the presence of a line segment with a particular orientation located within its receptive field, especially when the line moves perpendicularly to its orientation.
     • Hypercomplex Cell
       • A neuron in the visual cortex that responds to the presence of a line segment with a particular orientation that enda at a particular point within the cell's receptive field.

2. Dimensions

   • Hue
     • One of the perceptual dimensions of color; the dominant wavelength.
   • Brightness
     • One of the perceptual dimensions of color; intensity.
     • Sine-Wave Grating
       • A series of straight parallel bands varying continuously in brightness according to a sine-wave function, along a line perpendicular to their lengths.
       • Spatial Frequency
         • The relative width of the bands in a sine-wave grating, measured in cycles per degree of visual angle.
   • Saturation
     • One of the perceptual dimensions of color; purity.

3. Movement

   • Vergence Movement
     • The cooperative movement of the eyes, which ensures that the image of an object falls on identical portions of both retinas.
   • Saccadic Movement
     • The rapid, jerky movement of the eyes used in scanning a visual scene.
   • Pursuit movement
     • The movement that the eyes make to maintain an image of a moving object on the fovea.
   • Optic Flow
     • The complex motion of points in the visual field caused by relative movement between the observer and environment; provides information about the relative distances of objects from the observer and of the relative direction of movement.

4. Bygging

   • Retina
     • The neural tissue and photoreceptive cells located on the inner surface of the posterior portion of the eye.
     • Fovea
       • The region of the retina that mediates the most acute vision of  birds and higher mammals. Color-sensitive cones constitute the only type of photoreceptor found in the fovea.
     • Optic Disk
       • The location of the exit point from the retina of the fibers of the ganglion cells that form the optic nerve;  responsible  for the blind spot.
     • Bipolar Cell Layer
       • Bipolar Cell
         • A bipolar neuron located in the middle layer of the retina, conveying information from the photoreceptors to the ganglion cells.
         • Amacrine Cell
           • A neuron in the retina that interconnects adjacent ganglion cells and the inner processes of the bipolar cells.
       • Horizontal Cell
         • A neuron in the retina that interconnects adjacent photoreceptors and the outer processes of the bipolar cells.
     • Ganglion Cell Layer
       • Ganglion Cell
         • A neuron located in the retina that receives visual information from bipolar cells; its axons give rise to the optic nerve.
     • Photoreceptor Layer
       • Photoreceptor
         • One of the receptor cells of the retina; transduces photic energy into electrical potentials.
         • Rod
           • One of the receptor cells of the retina; sensitive to light of low intensity.
           • Lamella
             • A layer of membrane containing photopigments; found in rods and cones of the retina.
             • Retinal
               • A chemical synthesized from vitamin A; joins with an opsin to form a photopigment.
               • Photopigment
                 • A protein dye bonded to retinal, a substance derived from vitamin A; responsible for transduction of visual information.
             • Opsin
               • A class of protein that, together with retinal, constitutes the photopigments.
               • Rhodopsin
                 • A particular opsin found in rods.
         • Cone
           • One of the receptor cells of the retina; maximally sensitive to one of three different wavelengths of light and hence encodes color vision.
   • Thalamus
     • Dorsal Lateral Geniculate Nucleus
       • A group of cell bodies within the lateral geniculate body of the thalamus; receives inputs from the retina and projects to the primary visual cortex.
       • Magnocellular Layer
         • One of the inner rwo layers of neurons in the dorsal lateral geniculate nucleus; transmits information necessary for the perception of form, movement, depth, and small differences in brightness to the primary visual cortex.
       • Parvocellular Layer
         • One of the four outer layers of neurons in the dorsal lateral geniculate nucleus; transmits information necessary for perception of color and fine details to the primary visual cortex.
       • Koniocellular Sublayer
         • One of the sublayers of neurons in the dorsal lateral geniculare nucleus found ventral to each of the magnocellular and parvocellular layers; transmits information from short-wavelength ("blue") cones to the primary visual cortex.
   • Calcarine Fissure
     • A horizontal fissure on the inner surface of the posterior cerebral cortex; the location of the primary visual cortex.
     • Striate Cortex
       • The primary visual cortex.
       • Simple Cell
         • An orientation-sensitive neuron in the striate cortex whose receptive field is organized in an opponent fashion.
       • Extrastriate Cortex
         • A region of visual association cortex; receives fibers from the striate cortex and from the superior colliculi and projects to the inferior temporal cortex.
         • Lateral Occipital Cortex
           • A region of the extrastriate cortex, involved in perception of objects other that people's bodies and faces.
           • Extrastriate Body Area
             • A region of the visual association cortex located in the lateral occipitotemporal cortex; involved in perception of the human body and body parts other than faces.
       • Dorsal Stream
         • A system of interconnected regions of visual cortex involved in the perception of spatial location, beginning with the striate cortex and ending with the posterior parietal cortex.
         • Posterior Temporal Cortex
           • The highest level of the dorsal stream of the visual association cortex; involved in perception of movement and spatial location.
         • Intraparietal Sulcus
           • The end of the dorsal stream of the visual association cortex; involved in perception of location, visual attention and control of eye and hand movements.
       • Ventral Stream
         • A system of interconnected regions of visual cortex involved in the perception of form, beginning with the striate cortex and ending with the inferior temporal cortex
         • Inferior Temporal Cortex
           • The highest level of the ventral stream of the visual association cortex; involved in perception of objects, including people's bodies and faces.
           • Fusiform Face Area
             • A region of the visual association cortex located in the inferior temporal; ivolved in perception of faces and other complex objects that require expertise to recognize.
     • Optic Chiasm
       • A cross-shaped connection between the optic nerves, located below the base of the brain, just anterior to the pituitary gland.
   • Workings
     • Accommodation
       • Changes in the thickness of the lens of the eye, accomplished by the ciliary muscles, that focus images of near or distant objects on the retina.
     • Defects
       • Protanopia
         • An inherited form of defective color vision in which red and green hues are confused; "red" cones are filled with "green" cone opsin.
       • Deuteranopia
         • An inherited form of defective color vision in which red and green hues are confused; "green" cones are filled with "red" cone opsin.
       • Tritanopia
         • An inherited form of defective color vision in which hues with short wavelengths are confused; "blue" cones are either lacking or faulty.
       • Cerebral Achromatopsia
         • Inability to discriminate among different hues; caused my damage to area V8 of the visual cortex.
       • Visual Agnosia
         • Deficits in visual perception in the absence of blindness; caused by brain damage.
       • Prosopagnosia
         • Failure to recognize particular people by the sight of their faces.
       • Akinetopsia
         • Inability to perceive movement, caused by damage to area V5 of the visual association cortex.
   • Limbic Cortex
     • Parahippocampal Place Area
       • A region of limbic cortex on the medial temporal lobe; involved in perception of particular places.

5. Vision

   • Negative Afterimage
     • The image seen after a portion of the retina is exposed to an intense visual stimulus; consists of colors complementary to those of the physical stimulus.
   • Complementary Colors
     • Colors that make white or gray when mixed together.
   • Retinal Disparity
     • The fact that points on objects located at different distances from the observer will fall on slightly different locations on the two retinas; provides the basis for stereopsis.
   • Ocular Dominance
     • The extent to which a particular neuron recieves more input from ove eye than from the other.
   • Color Constancy
     • The relatively constant appearance of the colors of objects viewed under varying light conditions.

6. Cytochrome Oxidase

   • The central region of a module if the primary visual cortex, revealed by a stain for cytochrome oxidase; contains wavelength-sensitive neurons; part of the parvocellular system.