a quantum of visible light or other form of electromagnetic radiation demostrating both particle and wave properties
Cornea
the transparent window into the eyeball
Aqueous humor
the watery fluid in the anterior chamber of the eye
Crystalline lens
the lens inside the eye that enables changing focus
Vitreous humor
the transparent fluid that fills the vitreous chamber in the posterior part of the eye
Retina
light sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve
Fundus
the back layer of the retina-what the eye doctor sees through an ophthalmoscope
Photoreceptors
light sensitive receptors in the retina
Rods
photoreceptors specialized for night vision
Coes
photoreceptors specialized for daylight vision
Synaptic terminal
the location where axons terminate at the synapse for transmission of information by release of a chemical transmitter
chromophore
the light catching part of the visual pigments of the retina
the visual pigment found in the rods
rhodopsin
Hyperpolerization
an increase in membrane potential where the inner membrane surface becomes more negative than the outer membrane surface
Graded potential
an electrical potential that can vary continuously in amplitude
Fovea
small depression at the center of the macula of the retina
Horizontal cells
specialized retinal cells that contact both photoreceptors and bipolar cells
Lateral inhibition
antagonist neural interaction b/w adjacent regions of the retina
Bipolar cells
retinal cells that synapse with either rods or cones(not both) and with horizontal cells, and then pass the signals on to ganglion cells
Visual Acuity
a measure of the finest detail that can be resolved by the eyes
Retinal cells that receive visualinfo. from photoreceptors via 2 intermediate neuron types (bipolar cells and amacrine cells) and transmit info to the brain and midbrain
ganglion cells
P ganglion cells
receive excitatory input from single midget bipolar cells
M ganglion cells
resembling little umbrellas that receive excitatory input from diffuse bipolr cells and feed the magnocellular layer of the lateral geniculate nucleus
Receptive field
the region on the retina in which visual stimuli influence a neuron's firing rate
A cell that depolarizes in response to an increase in light intensity in its receptive field center
ON-center cell
The difference in luminance between an object and the background, or between lighter and darker parts of the same object
contrast
Spatial Frequency
the number of cycles of a grating per unit of visual angle (usually specified in degrees)
Cycles per degree
the number of dark and bright bars per degree of visual angle
A function describing how the sensitivity to contrast depends on the spatial frequency (size) of the stimulus
Contrast sensitivity function (CSF)
Contrast threshold
the smallest amount of contrast required to detect a pattern
Magnocellular layers
the neurons in the bottom 2 layers of the lateral geniculate nucleus
physically larger than those in the top 4 layers
The neurons in the top 4 layers of the LGN, which are physically smaller than those in the bottom 2 layers
parvocellular layers
Primary Visual Cortex (V1)
the area of the cerebral cortext of the brain that receives direct inputs from the lateral geniculate nucleus
responsible for processing visual info.
also called striate cortex
Cortical magnification
the amount of cortical area devoted to a specific region the visual field
Orientation tuning
the tendancy of neurons in the striate cortex to respond optimally to certain orientations
Column
a vertical arrangement of neurons
Cytochrome oxidase (CO)
an enzyme used to reveal the regular array of CO blobs.