Glossary
Accommodation
The process by which the eye's lens changes shape to focus near or far objects on the retina.
Example:
As you shift your gaze from a distant mountain to a nearby flower, your lens performs accommodation to keep both objects in focus.
Afterimage effect
A visual illusion where an image continues to appear briefly after exposure to the original image has ceased, often in complementary colors.
Example:
If you stare at a bright yellow circle for a minute and then look at a blank white wall, you'll likely see a blue afterimage effect.
Amplitude
The height of a wave, which determines the intensity or brightness of light.
Example:
A light with high amplitude would appear very bright, like a powerful spotlight, compared to a dim flashlight.
Astigmatism
A condition in which the eye does not focus light evenly onto the retina, resulting in distorted or blurry vision at all distances.
Example:
Someone with astigmatism might see lights at night with a starburst or streaky effect due to the irregular curvature of their cornea.
Bipolar cells
Neurons in the retina that receive signals from photoreceptors (rods and cones) and transmit them to ganglion cells.
Example:
After light stimulates the rods and cones, the bipolar cells act as an intermediary, passing the visual information along the neural pathway.
Blind Spot
The point at which the optic nerve leaves the eye, creating a 'blind' spot because no receptor cells are located there.
Example:
You don't typically notice your blind spot because your brain 'fills in' the missing visual information based on surrounding details.
Colorblindness
A deficiency in the ability to distinguish between certain colors, typically due to a lack of one or more types of cone photoreceptors.
Example:
A person with red-green colorblindness might struggle to differentiate between traffic lights or certain shades of clothing.
Cones
Photoreceptors in the retina that detect fine detail and color, functioning best in bright light and concentrated in the fovea.
Example:
To appreciate the vibrant colors of a painting, your cones are essential, as they are responsible for color vision.
Cornea
The transparent outer layer of the eye that protects the eye and helps to bend light, initiating the focusing process.
Example:
Dust in your eye often lands on the cornea, causing irritation until it's flushed out.
Dark Adaptation
The process by which the eyes become more sensitive to light in low illumination, primarily due to the regeneration of rhodopsin in rods.
Example:
After walking into a dark movie theater, it takes a few minutes for your eyes to undergo dark adaptation before you can see the seats.
Electromagnetic Spectrum
The entire range of electromagnetic radiation, including visible light, radio waves, X-rays, and microwaves.
Example:
While humans can only see a small portion of the electromagnetic spectrum, some animals can perceive ultraviolet or infrared light.
Farsightedness (Hyperopia)
A condition in which distant objects are seen more clearly than nearby objects because the eye focuses images behind the retina.
Example:
An individual with farsightedness might need reading glasses to see the words on a page clearly, but can see distant objects without issue.
Feature Detectors
Specialized neurons in the visual cortex that respond to specific features of a visual stimulus, such as shape, angle, or movement.
Example:
When you see a horizontal line, specific feature detectors in your brain become active, signaling the presence of that particular orientation.
Ganglion cells
Neurons in the retina whose axons form the optic nerve, carrying visual information from the eye to the brain.
Example:
The collective axons of millions of ganglion cells bundle together to form the optic nerve, exiting the back of the eye.
Hue
The dimension of color that is determined by the wavelength of light; what we know as the color names like blue, green, and red.
Example:
When you look at a rainbow, each distinct color, or hue, is caused by a different wavelength of light.
Intensity
The amount of energy in a light wave, perceived as brightness, determined by the wave's amplitude.
Example:
As the sun sets, the intensity of the light decreases, making everything appear dimmer.
Iris
A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.
Example:
The unique pattern and color of your iris are what give your eyes their distinct appearance, like blue, brown, or green.
Lens
The transparent structure behind the pupil that changes shape to help focus images on the retina.
Example:
When you read a book, your eye's lens adjusts its shape to bring the words into sharp focus on your retina.
Nearsightedness (Myopia)
A condition in which nearby objects are seen more clearly than distant objects because the eye focuses images in front of the retina.
Example:
Someone with nearsightedness might be able to read a book perfectly but struggle to see street signs clearly while driving.
Opponent-Process Theory
The theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision, where some neurons are excited by one color and inhibited by its opponent.
Example:
The opponent-process theory explains why staring at a green flag and then looking at a white wall makes you see a red afterimage.
Optic Chiasm
The point in the brain where the optic nerves from each eye cross over, sending visual information from the left visual field to the right hemisphere and vice versa.
Example:
Information from your left eye's right visual field crosses at the optic chiasm to be processed by the left side of your brain.
Optic Nerve
The nerve that carries neural impulses from the eye to the brain, specifically to the thalamus and then the visual cortex.
Example:
Damage to the optic nerve can result in partial or complete blindness, as it's the main conduit for visual information to the brain.
Parallel Processing
The brain's ability to process multiple aspects of a problem or visual scene simultaneously, such as color, motion, form, and depth.
Example:
When you see a moving car, your brain uses parallel processing to simultaneously analyze its color, shape, speed, and distance.
Photoreceptors
Specialized cells in the retina (rods and cones) that detect light and convert it into neural signals.
Example:
Without functioning photoreceptors, you would be unable to see anything, as they are the initial light-detecting cells.
Pupil
The adjustable opening in the center of the eye through which light enters.
Example:
In a dark room, your pupil will dilate to allow more light to enter your eye, helping you see better.
Retina
The light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
Example:
The image of a tree is projected upside down onto your retina, where it's converted into neural signals.
Rods
Photoreceptors in the retina that detect black, white, and gray, and are responsible for peripheral and dim-light vision.
Example:
When you walk into a dimly lit room, your rods become active, allowing you to navigate even without much color perception.
Supercell Clusters
Teams of cells in the visual cortex that respond to more complex patterns, such as faces or specific objects.
Example:
Recognizing your grandmother's face, even from a distance, involves the activation of supercell clusters that process complex visual information.
Thalamus
A brain's sensory control center, located on top of the brainstem, that relays sensory messages to the visual cortex (except for smell).
Example:
Before visual information reaches the visual cortex for interpretation, it first stops at the thalamus, which acts as a sensory switchboard.
Transduction
The process by which sensory receptors convert physical energy (like light or sound) into neural signals that the brain can understand.
Example:
When light hits your eye, the photoreceptors in your retina perform transduction, changing light energy into electrical impulses.
Visual Cortex
The area of the cerebral cortex located in the occipital lobe that receives and processes visual information.
Example:
When you recognize a familiar face, your visual cortex is actively processing the complex patterns of light received from your eyes.
Wavelength
The distance between successive peaks or troughs of a wave, which determines the hue (color) of visible light.
Example:
A short wavelength of light would be perceived as blue or violet, while a long wavelength would appear red.
Young-Helmholtz Trichromatic Theory
The theory that the retina contains three different color receptors (red, green, and blue) which, when stimulated in combination, can produce the perception of any color.
Example:
This theory explains why mixing red, green, and blue lights can create a wide range of colors on a TV screen, as our eyes have Young-Helmholtz Trichromatic Theory receptors.