Eye and Optics
This transparent outer layer of the eye provides most of the eye’s refraction to focus light on the retina.
What is the cornea?
This thin layer of neurons at the back of the eye converts light into neural signals.
What is the retina?
The axons of retinal ganglion cells form this nerve that carries visual information from the eye toward the brain.
What is the optic nerve (cranial nerve II)?
This term describes the region of space and stimulus features that alter the firing of a given sensory neuron.
What is a receptive field?
The three main psychological dimensions of color are brightness, hue, and this dimension that describes how “pure” or grayish a color appears.
What is saturation?
This flexible structure changes shape during accommodation to fine-tune focus on near or far objects.
What is the lens?
These photoreceptors are concentrated in the fovea, support high acuity and color vision, and operate best in bright light.
What are cones?
This X-shaped structure is where some optic nerve fibers cross the midline on their way to the brain.
What is the optic chiasm?
Bipolar and ganglion cells in the retina often have this type of receptive field, with an excitatory center and inhibitory surround, or vice versa.
What is a concentric center-surround receptive field (on-center/off-surround or off-center/on-surround)?
The trichromatic hypothesis proposes that human color vision is based on three types of cones, commonly labeled by these letters according to their peak wavelength sensitivities.
What are S, M, and L cones?
This process, controlled by the ciliary muscles, changes the focal length of the lens so near objects come into focus on the retina.
What is accommodation?
The rod-based scotopic system is highly sensitive to dim light, but it is poor at this aspect of vision, which is sharpest in the fovea.
What is visual acuity?
Most optic tract axons synapse in this thalamic nucleus before projecting via the optic radiations to primary visual cortex.
What is the lateral geniculate nucleus (LGN)
This process, where active receptor or bipolar cells inhibit their neighbors, sharpens edges but also contributes to brightness illusions like those seen in Mach bands.
What is lateral inhibition?
Because the genes for M and L cone pigments lie on this chromosome, red-green color deficiencies are more common in males than in females.
What is the X chromosome?
In this common condition, the eyeball is too long, so distant objects are focused in front of the retina, making far vision blurry.
What is myopia (nearsightedness)?
In darkness, photoreceptors continuously release neurotransmitter; when light hits the photopigment, the cell does this to its membrane potential and releases less transmitter.
What is hyperpolarize?
Because nasal retinal fibers cross and temporal fibers do not, visual information from the left visual field is processed in this cerebral hemisphere.
What is the right hemisphere?
In V1, these cells respond best to bars or edges of a particular orientation at a specific location, but do not require motion to fire strongly.
What are simple cortical cells?
This color theory, associated with Ewald Hering, proposes three opponent pairs: red–green, blue–yellow, and black–white.
What is the opponent-process hypothesis of color vision?
This opening in the iris changes size under sympathetic and parasympathetic control but accounts for only about a 16-fold change in light entering the eye, far less than the full range of visual sensitivity.
What is the pupil?
This high-acuity region of the retina has a dense packing of cones and a “pit” where light reaches photoreceptors with minimal obstruction from other retinal layers.
What is the fovea?
The orderly point-to-point mapping from the retina to V1, in which neighboring points in visual space activate neighboring cortical neurons, is known by this term.
What is retinotopic mapping (or a topographic projection of the visual field)?
Also called area MT, this extrastriate region contains neurons highly selective for direction and speed of motion, and lesions here can cause an inability to perceive smooth motion.
What is area V5 (the medial temporal area)?
This cortical area is rich in hue-selective neurons, responds strongly to complex color patterns and radial/concentric designs, and is critical for normal color perception.
What is area V4?