Sensation and Perception

Top-down processing

Top-down processing

Information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.

Bottom-up processing

Analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information.

Sensation

The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

Perception

The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

Absolute threshold

The minimum stimulation needed to detect a particular stimulus 50 percent of the time.

Subliminal threshold

Below one’s absolute threshold for conscious awareness.

Diference threshold

The minimum difference between two stimuli required for detection 50 percent of the time. The difference threshold is experienced as a just noticeable difference.

Weber’s law

The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount).

Signal detection theory

A theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes that there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness.

Sensory adaptation

Diminished sensitivity as a consequence of constant stimulation.

Transduction

Conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as the senses, into neural impulses our brain can interpret.

Cornea

Protects the eye and bends light to provide focus.

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.

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.

Lens

The transparent structure behind the pupil that changes shape to help focus images on the retina.

Visual accommodation

The process by which the eye’s lens changes shape to focus near or far objects on the retina.

Nearsightedness

A condition in which close objects apear clearly, but far ones don’t.

Farsightedness

A vision condition in which nearby objects are blurry.

Optic nerve

The nerve that carries neural impulses from the eye to the brain.

Blind spot

The point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.

Fovea

The central focal point in the retina, around which the eye’s cones cluster.

Photoreceptors

Special cells in the eye’s retina that are responsible for converting light into sight that are sent to the brain.

Trichromatic theory of color

The theory that the retina contains three different color receptors—one most sensitive to red, one to green, one to blue—which, when stimulated in combination, can produce the perception of any color.

Ishihara test

Test for color blindness

Outer ear

Channels the waves through the auditory canal to the eardrum causing it to vibrate.

Middle ear

The chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

Inner ear

The innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

Cochlea

A coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.

Opponent process theory of color

The theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision.

Kinesthetic sense

The sense of body position and movement of body parts relative to each other.

Vestibular sense

The sense of body movement and position, including the sense of balance.

Taste buds

Taste receptor cells in mouth; responsible for sense of taste

Olfactory nerve

The nerve that carries smell impulses from the nose to the brain.

Rods

Retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don’t respond.

Cones

Retinal receptor cells that are concentrated near the center of the retina and function in daylight. The cones detect fine detail and give rise to color sensations.

Selective attention

The focusing of conscious awareness on a particular stimulus.

Perceptual illusions

The misinterpretation of a real external, sensory experience.

Visual capture

The tendency for vision to override the other senses.

Grouping

The perceptual tendency to organize stimuli into coherent groups.

Closure

We fill in gaps to create a complete, whole object.

Depth perception

The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.

Binocular cues

Depth cues, such as retinal disparity, that depend on the use of two eyes.

Retinal disparity

A binocular cue for perceiving depth: By comparing images from the retinas in the two eyes, the brain computes distance— the greater the difference between the two images, the closer the object.

Convergence

Enables the slightly different images of an object seen by each eye to come together and form a single image.

Relative size

If we assume 2 objects are similar in size, most people perceive the one that casts the smaller retinal image as farther away.

Perceptual set

A mental predisposition to perceive 1 thing and not another.

Monocular cues

Depth cues, such as interposition and linear perspective, available to either eye alone.

Interposition

A monocular depth cur occurring when 2 objects are in the same line of vision and the closer object, which is fully in view, partly conceals the farther object.

Relative clarity

Because light from distant objects passes through more light than closer objects, we perceive hazy objects to be farther away.

Texture gradient

The progressive decline in the resolution of textures as the viewer moves away from them.

Relative height

We perceive objects that are higher in our field of vision to be farther away than those that are lower.

Linear perspective

One of the monocular depth cues, arising from the principle that the size of an object’s visual image is a function of it’s distance from the eye. Thus, 2 objects appear closer together as the distance from them increases. (Railroad tracks)

Motion perception

The ability of the nervous system to discern the distance and speed of a moving object in relation to the eye that’s seeing the object.

Phi phenomenon

An illusion of movement created when two or more adjacent lights blink on and off in quick succession.

Perceptual constancy

Perceiving objects as unchanging (having consistent shapes, size, brightness, and color) even as illumination and retinal images change.

Color constancy

Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.

Relative motion

Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction.

Schemas

A concept or framework that organizes and interprets information.

Extrasensory perception

The controversial claim that perception can occur apart from sensory input; includes telepathy, clairvoyance, and precognition.

Telepathy

Mind-to-mind communication.

Clairvoyance

The power to see things that cannot be perceived by the senses

Precognition

Perceiving future events

Sensory interaction

The principle that one sense may influence another, as when the smell of food influences its taste.

Olfaction

The resulting experiences of smell.

Gustation

The perception of sensations that are usually described as having 1 or more taste qualities: sweet, salty, sour, bitter, or umami.