Glossary
Absolute Threshold
The minimum stimulation needed to detect a particular stimulus 50% of the time.
Example:
If you can hear a faint whisper from across the room only half the time it's spoken, that whisper is at your absolute threshold for sound.
Afterimages
Visual images that persist after a stimulus has been removed, often appearing in complementary colors due to the fatigue of specific color-sensitive cells.
Example:
If you stare at a bright yellow circle for a minute and then look at a blank white wall, you might see a blue afterimage.
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 and information from your other eye.
Blindsight
A condition in which a person can respond to visual stimuli without consciously perceiving them, often due to damage in the visual cortex.
Example:
Someone with blindsight might be able to navigate around obstacles in a hallway without consciously seeing them, demonstrating an unconscious visual awareness.
Color Vision Deficiency
An inability or decreased ability to see color or perceive color differences, typically due to damage or irregularities in the cones or ganglion cells.
Example:
A person with color vision deficiency might struggle to distinguish between red and green traffic lights.
Dark Adaptation
The process by which the eyes adjust to a sudden decrease in illumination, causing the rods to become more sensitive and the cones to become less active.
Example:
When you enter a dark cave, it takes a few minutes for your eyes to experience dark adaptation, allowing you to eventually see outlines of objects.
Dichromatism
A form of color vision deficiency where an individual has only two types of functioning cones instead of the normal three, leading to difficulty distinguishing certain color pairs.
Example:
Someone with dichromatism might see the world primarily in shades of blue and yellow, unable to differentiate between reds and greens.
Farsightedness (Hyperopia)
A condition in which distant objects are seen more clearly than nearby objects because the eyeball is too short and the image focuses behind the retina.
Example:
An individual with farsightedness might have difficulty reading small print up close but can see objects far away with clarity.
Image Processing
The brain's ability to organize and interpret raw visual data from the retina into a coherent and meaningful picture.
Example:
Even though a movie is just a rapid sequence of still images, your brain's image processing makes you perceive continuous motion.
Just Noticeable Difference (JND)
The smallest detectable change in a stimulus that can be detected 50% of the time.
Example:
If you're listening to music, the just noticeable difference is the smallest increase in volume you can detect.
Lens Accommodation
The process by which the eye's lens changes shape to focus near or far objects on the retina.
Example:
When you shift your gaze from a distant mountain to a nearby flower, your eye performs lens accommodation to bring the flower into sharp focus.
Light Adaptation
The process by which the eyes adjust to a sudden increase in illumination, causing the cones to become more active and the rods to become less sensitive.
Example:
Stepping out of a dark movie theater into bright sunlight causes your eyes to undergo light adaptation, making the initial brightness overwhelming.
Monochromatism
A rare form of color vision deficiency where an individual has no functioning cones, resulting in complete absence of color vision and seeing only shades of gray.
Example:
A person experiencing monochromatism would perceive a vibrant rainbow as a spectrum of varying shades of gray.
Nearsightedness (Myopia)
A condition in which nearby objects are seen more clearly than distant objects because the eyeball is too long and the image focuses in front of the retina.
Example:
Someone with nearsightedness might struggle to read street signs from a distance but can easily read a book held close to their face.
Occipital Lobes
The rearmost lobe of the cerebral cortex, primarily responsible for processing visual information.
Example:
Damage to the occipital lobes can impair a person's ability to recognize objects or faces, even if their eyes are functioning normally.
Opponent-Process Theory
The theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision; for example, some cells are stimulated by green and inhibited by red.
Example:
Staring at a green square and then looking at a white wall often produces a red afterimage, which is explained by the Opponent-Process Theory.
Perception
The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.
Example:
After your eyes sense the light, your brain engages in perception to interpret those light patterns as a familiar face.
Prosopagnosia (Face Blindness)
A neurological disorder characterized by the inability to recognize familiar faces, including one's own face, despite otherwise intact visual processing.
Example:
A person with prosopagnosia might rely on a friend's voice or distinctive clothing to identify them, as their face appears unfamiliar.
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:
When you look at a bright light, the image is focused onto your retina at the back of your eye.
Rods
Photoreceptor cells in the retina that detect black, white, and gray, and are sensitive to movement; they are essential for peripheral vision and vision in dim light.
Example:
When you walk into a dimly lit room, your rods are primarily responsible for helping you navigate and see shapes in the low light.
Sensation
The process by which our sensory receptors and nervous system receive and encode raw physical energy from the environment.
Example:
When light waves hit your eyes, your retina is engaged in sensation by detecting the incoming visual information.
Sensory Adaptation
A decrease in sensitivity to a constant level of stimulation over time.
Example:
When you first jump into a cold swimming pool, it feels frigid, but after a few minutes, you experience sensory adaptation and the water no longer feels as cold.
Sensory Interaction
The principle that one sense may influence another, as when the smell of food influences its taste.
Example:
When you have a stuffy nose, food often tastes bland because your sense of smell is crucial for the full experience of flavor, demonstrating sensory interaction.
Synesthesia
A rare neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.
Example:
A person with synesthesia might see the color blue whenever they hear the note C sharp played on a piano.
Transduction
The conversion of one form of energy into another, specifically the process by which sensory stimuli are converted into neural signals the brain can understand.
Example:
When sound waves enter your ear, your cochlea performs transduction by converting these vibrations into electrical signals for the brain.
Trichromatic Theory
The theory that the retina contains three different color receptors (red, green, blue) which, when stimulated in combination, can produce the perception of any color.
Example:
Mixing red, green, and blue lights on a stage to create various hues is an application of the Trichromatic Theory of color vision.
Weber's Law
A principle stating that for an average person to perceive a difference, two stimuli must differ by a constant minimum percentage, not a constant amount.
Example:
You'd more easily notice an extra ounce added to a 1-ounce letter than to a 10-pound package, illustrating Weber's Law.