Chapter 3: Spatial Vision - From Spots to Stripes Flashcards
contrast
The difference in luminance between an object and the background, or between lighter and darker parts of the same object.
acuity
The smallest spatial detail taht can be resolved at 100% contrast.
cycle
For a grating, a pair consisting of one dark bar and one bright bar.
visual angle
The angle subtended by an object at the retina.
sine wave grating
A grating with a sinusoidal luminance profile as shown in Figure 3.4a
spatial frequency
The number of grating cycles (i.e., dark and bright bars) in a given unit of space.
cycles per degree
The number of grating cycles per degree of visual angle.
contrast sensitivity function (CSF)
A function describing how the sensitivity to contrast (defined as the reciprocal of the contrast threshold) depends on the spatial frequency (size) of the stimulus.
contrast threshold
The smallest amount of contrast required to detect a pattern.
lateral geniculate nucleus (LGN)
A structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.
magnocellular layer
Either of the bottom two neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers.
parvocellular layer
Any of the top four neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically smaller than those in the bottom two layers.
koniocellular cell
A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.
contralateral
Referring to the opposite side of the body (or brain).
ipsilateral
Referring to the same side of the body (or brain).
topographical mapping
The orderly mapping of the world in the lateral geniculate nucleus and the visual cortex.
primary visual cortex (V1), area 17, striate cortex
The area of the cerebral cortex of the brain that receives direct inputs from the lateral geniculate nucleus, as well as feedback from other brain areas.
cortical magnification
The amount of cortical area (usually specified i millimeters) devoted to a specific region (e.g., 1 degree) in the visual field.
visual crowding
The deleterious effect of clutter on peripheral object recognition.
orientation tuning
The tendency of neurons in striate cortex to respond optimally to certain orientations and less to others.
filter
An acoustic, electrical, electronic, or optic device, instrument, computer program, or neuron that allows the passage of some range of parameters (e.g., orientations, frequencies) and blocks the passage of others.
ocular dominance
The property of the receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other.
simple cell
A cortical neuron whose receptive field has clearly defined excitatory and inhibitory regions.
complex cell
A cortical neuron whose receptive field does not have clearly defined excitatory and inhibitory regions.
end stopping
The process by which a cell in the cortex first increases its firing rate as the bar length increases to fill up its receptive field, and then decreases its firing rate as the bar is lengthened further.
column
A vertical arrangement of neurons. Neurons within a single column tend to have similar receptive fields and similar orientation preferences.
hypercolumn
A 1-millimeter block of striate cortex containing two sets of columns, each covering every possible orientation (0-180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye.
cytochrome oxidase (CO)
An enzyme used to reveal the regular array of “CO blobs” which are spaced about 0.5 millimeter apart in the primary visual cortex.
adaptation
A reduction in response caused by prior or continuing stimulation.
tilt aftereffect
The perceptual illusion of tilt, produced by adaptation to a pattern of a given orientation.
spatial-frequency channel
A pattern analyzer, implemented by an ensemble of cortical neurons, in which each set of neurons is tuned to a limited range of spatial frequencies.
critical period
A phase in the life span during which abnormal early experience can alter normal neuronal development.
amblyopia
A developmental disorder characterized by reduced spatial vision in an otherwise healthy eye, even with proper correction for refractive error. Also known as lazy eye.
strabismus
A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye and on a nonfoveal area of the other (turned) eye.
anisometropia
A condition in which the two eyes have different refractive errors (e.g., one eye is farsighted and the other not).
