Psychology Core Concepts Chapter 3: Sensation and Perception

sensation

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.

perception

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.

transduction

Transformation of one form of information into another - especially the transformation of stimulus information into nerve signals by the sense organs. As a result of transduction, the brain interprets the incoming light waves from a ripe tomato as red.

absolute threshold

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

difference threshold

The smallest amount by which stimulus can be changed and the difference be detected half the time.

Weber's law

The concept 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 small when the stimulus intensity is low.

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 contrast to older theories from psychophysics, signal detection theory takes observer characteristics into account.

sensory adaptation

Loss of responsiveness in receptor calls after stimulation has remained unchanged for a while, as when a swimmer becomes adapted to the temperature of the water.

retina

The thin light-sensitive layer at the back of the eyeball. The retina contains millions of photoreceptors and other nerve cells.

photoreceptors

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.

rods

Photoreceptors in the retina that are especially sensitive to dim light but not tor colours. Strange as it may see, they are rod-shaped.

cones

Photoreceptors in the retina that are especially sensitive to colours but not to dim light. You may have guessed that the cones are cone-shaped.

fovea

The tiny area of sharpest vision in the retina.

optic nerve

The bundle of neurons that carries visual information form the retina to the brain.

blind spot

The point where the optic nerve exits the eye and where there are no photoreceptors. Any stimulus that falls on this area cannot be seen.

brightness

A psychological sensation cause by the intensity (amplitude) of light waves.

colour

Also called hue. Colour 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 lights.

electromagnetic spectrum

The entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light.

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.

trichromatic theory

The idea that colours are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. The trichcromatic (three-colour) theory explains the earliest stage of colour sensation. In honor of its originators, this is sometimes called the Young-Helmholtz theory.

opponent-process theory

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

afterimages

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

colour blindness

Typically a genetic disorder (although sometimes the result of trauma, as in the case of Jonathan) that prevents an individual from discriminating certain colours. The most common form is red-green colour blindness.

frequency

The number of cycles completed by a wave in a second.

amplitude

The physical strength of a wave. This is shown on graphs as the height of the wave.

tympanic membrane

The eardrum.

cochlea

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

basilar membrane

A thin strip of tissue sensitive to vibratins 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.

pitch

A sensory characteristic of sound produced by the frequency of the sound wave.

loudness

A sensory characteristic of sound produced by the amplitude (intensity) of the sound wave.

timbre

The quality of a sound wave that derives form the wave's complexity (combination of pure tones). Timbre comes from the Greek word for "drum," as does the term tympanic membrane, or eardrum.

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.

kinesthetic sense

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

pheromones

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.

olfaction

The sense of smell.

gustation

The sense of taste, from the same word root as "gusto"; also called the gustatory sense.

skin senses

Sensory systems for processing touch, warmth, cold, texture, and pain.

synesthesia

The mixing of sensations across senosort modalities, as in tasting shapes or seeing colours associated with numbers.

gate-control theory

An explanation for pain control that proposes we have a neural "gate" that can, under some circumstances, block incoming pain signals.

placebo

Substance that appears to be a drug but is not. Placebos are often referred to as "sugar pills" because they might contain only sugar rather than a real drug.

placebo effect

A response to a placebo (a fake drug) caused by the belief that it is a real drug.

percept

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

what pathway

A neural pathway, projecting from the primary visual cortex to the temporal lobe, which involves identifying objects.

where pathway

A neural pathway that projects visual information to the parietal lobe; responsible form locating objects in space.

blindsight

The ability to locate objects despite damage to the visual system making it impossible for a person consciously to see and identify objects. Blindsight is thought to involve unconscious visual processing in the where pathway.

feature detectors

Cells 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 "blind") the results of many sensory operations into a single percept. This occurs, for example, when sensations of colour, 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.

top-down processing

Perceptual analysis that emphasizes the perceiver's expectations, concept memories, and the 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.

bottom-up processing

Perceptual analysis that emphasizes characteristics of the stimulus, rather than our concepts and expectations. "Bottom" refers to the stimulus, which occurs at step one of perceptual processing.

perceptual constancy

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

inattentional blindness

A failure to notice changes occurring in one's visual field, apparently caused by narrowing the focus of one's attention.

change blindness

A perceptual failure to notice that a visual scene has changed from the way it had appeared previously. Unlike inattentional blindness, change blindness requires comparing a current sense to one from the past, stored in memory.

illusion

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 hallucination.)

ambiguous figures

Images that can be interpreted in more than one way. There is no "right" way to see an ambiguous figure.

Gestalt psychology

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

figure

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

ground

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

closure

The Gestalt principle that identifies the tendency to fill in pages in 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 connected 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 organisation, 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.

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 is a given context - as when a person who is afraid interprets an unfamiliar sound as a treat.

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.