Vision Flashcards
In 1838, he held that whatever excited a particular nerve establishes a special kind of energy unique to that nerve. Any activity by a particular nerve always conveys the same kind of information to the brain.
Johannes Muller
The principle that any impulse in a given nerve sends the same kind of message to the brain.
Law of Specific Nerve Energies
The coding of visual information in the brain does not duplicate the shape of the object that one sees.
From Neuronal Activity to Perception
Route Within the Retina
Retina - Bipolar Cells - Ganglion Cells - Brain (in the form of optic nerve)
It is numerous and diverse and atleast 29 types have been identified so far. It gets information from bipolar cells and sends it to other bipolar cells, other amacrine cells, or ganglion cells.
Amacrine Cells
The point at which the axons of the ganglion cells exit.
Blind Spot
Measures about 3mm x 5 mm in the center of the retina.
Macula
The central portion of the macula, it is where the most precise vision comes in. It has the least impeded vision available.
Fovea
Has better acuity or sensitivity to detail.
Foveal Vision
Has better sensitivity to dim light. Can identify a shape much better than itself than it is surrounded by other objects.
Peripheral Vision
Receptors that are more abundant in the periphery of the human retina, responds to faint light but are bleached by bright light and thus not very useful in bright daylight.
Rods
Receptors that are more abundant in and around the fovea, are less active in dim light, and essential for color vision.
Cones
Chemicals that release energy when struck by light. They are stable in the dark and consist of 11-cis-retinal bound to proteins called opsins.
Photopigments
Requires comparing the responses of different kinds of cones.
Color Vision
Shortest visible wavelength about 350mm.
Violet
Longer wavelengths near 700mm.
Blue
Green
Yellow
Orange
Red
The first to recognize that color required a biological explanation. Proposed that we perceive color by comparing the responses of some small number of receptors.
Thomas Young
Believed that we perceive color through the relative rates of response by three kinds of cones.
Hermann von Helmhots
Three Cone Types
Short Wavelength
Medium Wavelength
Long Wavelength
Suggests that people discriminate among wavelengths by the ratio of activity across the three types of cones.
Trichromatic Theory
Suggests that we perceive color in terms of paired opposites: red vs. green, yellow vs. blue, and white vs. black.
Ewald Herring
The ability to recognize color of an object despite changes in lighting.
Color Constancy
Suggests that the cortex compares information from various parts of the retina to determine the brightness and color perception for each area.
Edwin Land
The inability to perceive color differences as most other people do.
Color Vision Deficiency (Color Blindness)
A nucleus of the thalamus specialized for visual perception.
Geniculate Nucleus
The point in space from which the light coming into the eye strikes the receptor.
Receptive Fields
A mechanism by which stimulation in any area of the Retina suppresses the responses in neighboring areas, thereby enhancing the contrast at light-dark borders.
Lateral Inhibition
Visual pathway begins its division if labor before it reaches the cerebral cortex. Different ganglion cells react differently to the same input.
Concurrent Pathways in the Retina and Lateral Geniculate
With smaller cell bodies and small receptive fields. Located mostly in or near the fovea. Well suited to detect visual details, very sensitive to color and each excited by some colors and inhibited by others.
Parvocellular Neurons
With larger cell bodies and receptive fields. Distributed fairly evenly throughout the retina, including the periphery. Respond strongly to moving stimuli and to large overall patterns but not to colors and visual details.
Magnocellular Neurons
Have smaller cell bodies and occur throughout the retina instead of being clustered near the fovea.
Koniocellular Neurons
It is the area of the cortex responsible for the first stage of visual processing. Responds to any kind of visual stimulus and is active even when we close our eyes.
Primary Visual Cortex (V1/Striate Cortex)
Processes the information further and transmits it to the additional areas.
Secondary Visual Cortex (V2)
The region of cortex located immediately in front of V2. Some controversy exists regarding the extent of this area, with some researchers proposing that this is in fact a complex of two or three functional subdivisions.
V3
An area particularly important for color contrast; it has cells that contribute to visual attention.
V4
Cells in this area respond selectively to a stimulus moving in a particular direction, almost independently of the size, shape, brightness, or color of the object.
Middle Temporal Cortex (MT/V5)
The inability to recognize objects despite otherwise satisfactory vision.
Visual Agnosia
They can read, recognize familiar people from their voices and sometimes even clothing, so their problem is specific to faces.
Prosopagnosia
Able to see objects but unable to determine whether they are moving or if so, in which direction or how fast.
Motion Blind
