AP Psychology Chapter 4: Sensation and Perception_Vocabulary

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Vocabulary words and definitions


The process by which stimulation of a sensory receptor produces neural impulses that the brain interprets as a sound, a visual image, an odor, a taste, a pain, or other sensory image. Sensation represents the first series of steps in processing of incoming information.
Simply as the process by which a stimulated receptor such as eyes or ears creates a pattern of neural messages that represent the stimulus in the brain, giving rise to our initial experience of the stimulus.


A process that makes sensory patterns meaningful. It is perception that makes these words meaningful, rather than just a string of visual patterns. To make this happen, perception draws heavily on memory, motivation, emotion, and other psychological processes.
A mental process that elaborates and assigns meaning to the incoming sensory patterns.


Transformation of one form of energy into another- especially the transformation of stimulus information into nerve signals by the sense organs. Without transduction, ripe tomatoes would not appear red (or pinkish-gray, in the case of tomatoes purchased in many grocery stores.)
The sensory process that converts physical energy, such as light or sound waves, into the form of neural messages.

Sensory adaptation

Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while, as when a swimmer becomes adapted to the temperature of the water.
The deminishing responsiveness of sensory systems to prolonged stimulation, as when you adapted to the feel of swimming in cool water.

Absolute threshold

The amount of stimulation necessary for a stimulus to be detected. In practice, this means that the presence or absence of a stimulus is detected correctly half the time over many trials.

Difference threshold

The smallest amount by which a stimulus can be changed and the difference be detected half the time.
The smallest physical difference between two stimuli that can still be recognized as a difference.

Just noticeable difference (JND)

Same as difference threshold.

Weber's law

This concept says that the size of a JND is proportional to the intensity of the stimulus; the JND is large when the stimulus intensity is high and is small when the stimulus intensity is low.
The size of the JND is proportional to the intensity of the stimulus.

Fecher's law

The magnitude of a stimulus can be estimated by the formula S=k log R, where S= sensation, R= stimulus, and k=a constant that differs for each sensory modality (Sight, touch, temperature, etc.).
Expresses the relationship between the actual magnitude of the stimulus and its perceived magnitude.

Steven's power law

A law of magnitude estimation that is more accurate than Fechner's law and covers a wider variety of stimuli. It is represented by the formula S= kl^a, where S= sensation, k= a constant, l= stimulus intensity, an a= a power exponent that depends on the sense being measured.
The third principle of stimulus detection.

Signal detection theory

Explains how we detect "signals," consisting of stimulation affecting our eyes, ears, nose, skin, and other sense organs. Signal detection theory says that sensation is a judgement the sensory system makes about incoming stimulation. Often, it occurs outside of consciousness. In contrasting to older theories from psychophysics, signals detection theory takes observer characteristics into account.
According to this sensation depends on the characterisitcs of the stimulus, the background stimulation, and the detector.


The thin, light-sensitive layer at the back of the eyeball. The retina contains millios of photoreceptors and other nerve cells.
The light-sensative chip in a digital camera.


Light-sensitive cells (neurons) in the retina that convert light energy to neural impulses. The photoreceptors are as far as light gets into the visual system.
Operate much like the tiny pixel receptors in a digital camera.


Photoreceptors in the retina that are especially sensitive to dim light but not to colors. Strange as it may seem, they are rod-shaped.
Detect low intensities of light at night, though cannot make the fine distinctions that give rise to our sensations of color.


Photoreceptor in the retina that are especially sensitive to colors but not to dim light. Cones are cone-shaped.
These come into play in birght light.


The tiny area of sharpest vision in the retina.
The cones concentrate in the very center of the retina, in a small region called the fovea, which gives us our sharpest vision.

Optic nerve

The bundle of neurons that carries visual information from the retina to the brain.
Transports visual information from the eye to the brain.

Blind spot

The point where the optic nerve exists the eye and where there are no photoreceptors. Any stimulus that falls on this area cannot be seen.
Located at the point where the optic nerve exits each eye, and the result is a gap in the visual field.


A psychological sensation caused by the intensity of light waves.
Comes from the intensity or amplitude of light, determined by how much light reaches the retina.


Also called hue. Color is not a property of things in the external world. Rather, it is a psychological sensation created in the brain from information obtained by the eyes from the wavelengths of visible light.

Electromagnetic spectrum

The entire rang of electromagnetic energy,including radio waves, X-rays, microwaves, and visible light.
The light we can see occupies but a tiny segment of the vast electromagnetic spectrum.

Visible spectrum

The tiny part of the electromagnetic spectrum to which our eyes are sensitive. The visible spectrum of other creatures may be slightly different from our own.
Our only access to this electromagnetic spectrum lies through a small visual "window" called the visible spectrum.

Trichoromatic theory

The idea that colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. The trichromatic theory explains the earliest stage of color sensation.

Opponent-process theory

The idea that cells in the visual system process colors in complementary pairs, such as red or green or as yellow or blue. The opponent-process theory explains color sensation from the bipolar cells onward in the visual system.


Sensations that linger after the stimulus is removed. Most visual afterimages are negative afterimages, which appear in reversed colors.

Color blindness

Typically a genetic disorder (although sometimes the result of trauma) that prevents an individual from discriminating certain colors. The most common form is re-green color blindness.


The number of cycles completed by a wave in a given amount of time, usually a second.
The number of vibrations or cycles the wave completes in a given amount of time; it is usually expressed in cycles per second.


The physical strength of a wave. This is usually measured from peak (top) to valley (bottom) on a graph of the wave.
The measure of the physical strength of the sound wave; it is defined in units of sound pressure or energy.

Tympanic membrane

The eardrum.
Vibrating waves of air enter the outer ear and strike the eardrum.


The primary organ of hearing; a coiled tube in the inner year, where sound waves are transduced into nerve messages.

Basilar membrane

A thin strip of tissue sensitive to vibrations in the cochlea. The basilar membrane contains hair cells connected to neurons. When a sound wave causes the hair cells to vibrate, the associated neurons become excited. As a result, the sound waves are converted (transduced) into nerve activity.
A thin strip if tissue running through the cochlea.


A sensory characteristic of sound produced by the frequency of the sound wave.
A sound waves's frequency determines the highness or lowness of a sound.


A sensory characteristic of sound produced by the amplitude (intensity) of the sound wave.
A sound is determined by its physical strength or amplitude (much as brightness is determined by the intensity of light).


The quality of a sound wave that derives from the wave's complexity (Combination of pure tones). Timbre comes from the Greek word "drum," as does the term tympanic membrane, or eardrum.
THe property that enables you to recognize a friend's voice on the phone or distinguish between the same song sung by different artists.

Conduction deafness

An inability to hear resulting from damage to structure of the middle or inner ear.
The ways in which sound waves are converted to nerve energy have been interfered with or interrupted.

Nerve deafness (Sensorineural Deafness)

An inability to hear, linked to a deficit in the body's ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers.
In this there is a problem with how the impulses from the oval window are sent to the brain; in other words, damage has occured to the auditory nerve or one higher auditory processing centers.

Vestibular sense

The sense of body orientation with respect to gravity. The vestibular sense is closely associated with the inner ear and, in fact, is carried to the brain on a branch of the auditory nerve.
The body position sense that orients us with respect to gravity.

Kinesthetic sense

The sense of body position and movement of body parts relative to each other (also called kinesthesis).
The other sense of body position and movement, keeps track of body parts relative to each other.


The sense of smell.
Involves a chain of biochemical events.


Chemical signals released by organisms to communicate with other members of their species. Pheromones are often used by animals as sexual attractants. It is unclear whether or not humans employ pheromones.


The sense of taste- from the same word root as "gusto"- also called the gustatory sense.
The four main qualities: sweet, sour, bitter, and salty.

Skin senses

Sensory systems for processing touch, warmth, cold, texture, and pain.
Connected to the somasensory cortex located in the brain's parital lobes.

Gate-control theory

An explanation for pain control that proposes we have a neural "gate" that can, under some circumstances, block incoming pain signals.
Melzack and Wall's (1965,1983)

Placebo effect

A response to a placebo (a fake drug), caused by subjects' belief that they are taking real drugs.
is common any drug deemed effective must prove itself stronger than a palcebo.


The meaningful product of perception- often an image that has been associated with concepts, memories of events, emotions, and motives.
What we perceive.

Feature detectors

Cell in the cortex that specialize in extracting certain features of a stimulus.

Binding problem

Refers to the process used by the brain to combine (or "bind") the results of many sensory operations into a single percept. This occurs, for example, when sensations of color, shape, boundary, and texture are combined to produce the percept of a person's face. No one knows exactly how the brain does this. Thus the binding problem is one of the major unsolved mysteries in psychology.

Bottom-up processing

Perceptual analysis that emphasizes characteristic of the stimulus, rather than our concepts and expectations. "Bottom" refers to the stimulus, which occurs at step one of perceptual processing.
Also known as stimulus-driven processing beacuse the resulting percept is determined or driven by stimulus features.

Top-down processing

Perceptual analysis that emphasizes the perceiver's expectations, concept memories, and other cognitive factors, rather than being driven by the characteristics of the stimulus. "Top" refers to a mental set in the brain- which stands at the "top" of the perceptual processing system.
Invokes a perceiver's goals, past experience, knowledge, expectation, memory, motivations, or cultural background in the interpretation of an object or event.

Perceptual constancy

The ability to recognize the same object as remaining "constant" under different conditions, such as changes in illumination, distance, or location.


You have experienced an illusion when you have a demonstrably incorrect perception of a stimulus pattern, especially one that also fools others who are observing the same stimulus. (If no one else sees it the way you do, you could be having a delusion or a hallucination.)

Ambiguous figures

Images that are capable of more than one interpretation. There is no "right" way to see an ambiguous figure.

Gestalt psychology

From a German word that means "whole" or "form" or "configuration." (A Gestalt is also a percept.) The Gestalt psychologist believed that much of perception is shaped by innate factors built into the brain.


The part of a pattern that commands attention. The figure stands out against the ground.


The part of a pattern that does not command attention; the background.


The Gestalt principle that identifies the tendency to fill in gaps figures and to see incomplete figures as complete.

Laws of perceptual grouping

The Gestalt principles of similarity, proximity, continuity, and common fate. These "laws" suggest how our brains prefer to group stimulus elements together to form a percept (Gestalt).

Law of similarity

The Gestalt principle that we tend to group similar objects together in our perceptions.

Law of proximity

The Gestalt principle that we tend to group objects together when they are near each other. Proximity means "nearness."

Law of continuity

The Gestalt principle that we prefer perceptions of connecte and continuous figures to disconnected and disjointed ones.

Law of common fate

The Gestalt principle that we tend to group similar objects together that share a common motion or destination.

Law of Pragnanz

The most general Gestalt principle, which states that the simplest organization, requiring the least cognitive effort, will emerge as the figure. Pragnanz shares a common root with pregnant, and so it carries the idea of a "fully developed figure." That is, our perceptual system prefers to see a fully developed Gestalt, such as a complete circle- as opposed to a broken circle.

Binocular cues

Information taken in by both eyes that aids in depth perception, including binocular convergence and retinal disparity.

Monocular cues

Information about depth that relies on the input of just one eye- includes relative size, light and shadow, interposition, relative motion, and atmospheric perspective.

Learning-based inference

The view that perception is primarily shaped by learning (or experience), rather than by innate factors.

Perceptual set

Readiness to detect a particular stimulus in a given context- as when a person who is afraid interprets an unfamiliar sound in the night as a threat.

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