Perception and Sensation: Key Terminology

Absolute Threshold: The lowest level of stimulation that a person can consciously detect $50$ percent of the time the stimulation is present.
Just Noticeable Difference (JND, or the Difference Threshold): The smallest difference between two stimuli that is detectable $50$ percent of the time.
Habituation: Tendency of the brain to stop attending to constant, unchanging information.
Bottom-Up Processing: The analysis of the smaller features to build up to a complete perception.
Perception: The method by which the sensations experienced at any given moment are interpreted and organized in some meaningful fashion.
Perceptual Set (Perceptual Expectancy): The tendency to perceive things a certain way because previous experiences or expectations influence those perceptions.

Cones: Visual sensory receptors found at the back of the retina, responsible for color vision and sharpness of vision.
Blind Spot: Area in the retina where the axons of the retinal ganglion cells exit the eye to form the optic nerve; insensitive to light.
Afterimages: Images that occur when a visual sensation persists for a brief time even after the original stimulus is removed.
Brightness Constancy: The tendency to perceive the apparent brightness of an object as the same even when the light conditions change.
Dark Adaptation: The recovery of the eye's sensitivity to visual stimuli in darkness after exposure to bright lights.
Light Adaptation: The recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness.
Müller-Lyer Illusion: An illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different.
Opponent-Process Theory: A theory of color vision that proposes visual neurons (or groups of neurons) are stimulated by light of one color and inhibited by light of another color.

Monocular Cues (Pictorial Depth Cues): Cues for perceiving depth based on one eye only.
Accommodation: As a monocular cue of depth perception; the brain's use of information about the changing thickness of the lens of the eye in response to looking at objects that are close or far away.
Aerial Perspective (Atmospheric): A monocular depth perception cue; the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater.
Interposition: A monocular depth perception cue; the assumption that an object that appears to be blocking part of another object is in front of the second object and closer to the viewer.
Linear Perspective: A monocular depth perception cue; the tendency for parallel lines to appear to converge on each other.
Motion Parallax: A monocular depth perception cue; the perception of motion of objects in which close objects appear to move more quickly than objects that are farther away.

Binocular Cues: Cues for perceiving depth based on both eyes.
Binocular Disparity: A binocular depth perception cue; the difference in images between the two eyes, which is greater for objects that are close and smaller for distant objects.
Convergence: A binocular depth perception cue; the rotation of the two eyes in their sockets to focus on a single object, resulting in greater convergence for closer objects and lesser convergence if objects are distant.

Frequency Theory: A theory of pitch that states that pitch is related to the speed of vibrations in the basilar membrane.
Hertz (Hz): Cycles or waves per second, a measurement of frequency.
Pitch: The psychological experience of sound that corresponds to the frequency of the sound waves; higher frequencies are perceived as higher pitches.
Place Theory: A theory of pitch that states that different pitches are experienced by the stimulation of hair cells in different locations on the organ of Corti.
Auditory Canal: Short tunnel that runs from the pinna to the eardrum.
Cochlea: Snail-shaped structure of the inner ear that is filled with fluid.
Auditory Nerve: Bundle of axons from the hair cells in the inner ear.
Pinna: The visible part of the ear.

Gustation: The sensation of a taste.
Olfaction (Olfactory Sense): The sensation of smell.
Olfactory Bulbs: Two bulblike projections of the brain located just above the sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells.
Kinesthesia: The awareness of body movement.
Proprioception: Awareness of where the body and body parts are located in relation to each other in space and to the ground.

Figure-Ground: The tendency to perceive objects, or figures, as existing on a background.
Closure: A Gestalt principle of perception; the tendency to complete figures that are incomplete.
Contiguity: A Gestalt principle of perception; the tendency to perceive two things that happen close together in time as being related.
Continuity: A Gestalt principle of perception; the tendency to perceive things as simply as possible with a continuous pattern rather than with a complex, broken-up pattern.
Proximity: A Gestalt principle of perception; the tendency to perceive objects that are close to each other as part of the same grouping; based on physical or geographical nearness.

Refractory Period: Time period in males just after orgasm in which the male cannot become aroused to another orgasm.