Sensation And Perception

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Sensation

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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 steps in processing of incoming information.

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Perception

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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.

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Transduction

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Transformation of one form of information 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.

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Absolute Threshold

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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.

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Difference Threshold

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

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Weber's Law

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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.

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Signal Detection Theory

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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.

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Sensory Adaptation

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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.

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Retina

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

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Photoreceptors

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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.

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Rods

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

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Cones

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

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Fovea

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The tiny area of sharpest vision in the retina.

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Optic Nerve

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

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Blind Spot

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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.

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Brightness

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

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Color

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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.

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Electromagnetic spectrum

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

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Visible Spectrum

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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.

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Trichromatic Theory

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

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Opponent-process Theory

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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.

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Afterimages

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

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Color Blindness

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

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Frequency

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

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Amplitude

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

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Tympanic Membrane

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The eardrum

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Cochlea

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

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Basilar Membrane

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A thin strip of tissue sensitive to vibrations in the cochlea. The basilar membrane contains 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.

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Pitch

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

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Loudness

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

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Timbre

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The quality of a sound wave that drives from the wave's complexity (combination of pure tones).

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Vestibular Sense

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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.

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Kinesthetic Sense

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

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Olfaction

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The sense of smell.

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Pheromones

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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.

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Gustation

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

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Skin Senses

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

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Synesthesia

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

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Gate-Control Theory

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

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Placebo Effect

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A response to a placebo (a fake drug), caused by the belief that they are real drugs.

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Percept

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

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Feature Detectors

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

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Binding Problem

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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.

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Top-down processing

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Perceptual analysis that emphasizes the perceiver's expectations, concept memories, and other cognitive factors, rather than being driven by the characteristic of the stimulus. "Top" refers to a mental set in the brain- which stands at the "top" of the perceptual processing system.

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Bottom-up Processing

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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.

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Perceptual Constancy

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

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Change Blindness

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A perceptual failure to notice changes occurring in one's visual field.

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Illusion

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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.)

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Ambiguous Figures

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

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Gestalt Psychology

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From the 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

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Figure

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

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Ground

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

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Closure

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

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Laws of perceptual grouping

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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.

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Law of Similarity

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

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Law of Proximity

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

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Law of Continuity

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

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Law of Common Fate

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

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Law Pragnanz

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The most general Gestalt Principle, which states that the simplest organization, requiring the least cognitive effort, will emerge as the figure.

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Learning-Based Inference

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

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Perceptual Set

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

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Binocular Sets

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

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Molecular Cues

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