chapter in review
The senses act as data reduction systems in order to prevent the brain from being overwhelmed by sensory input.
• Private sensations do not correspond perfectly to external stimuli. Studies in psychophysics relate physical energies to the sensations we experience.
• The sensory organs transduce a limited range of physical ener-gies into nerve impulses.
• The minimum amount of physical energy necessary to pro-duce a sensation defines the absolute threshold. The amount of change necessary to produce a just noticeable difference in a stimulus defines a difference threshold.
• There is evidence that subliminal perception occurs, but sub-liminal advertising is largely ineffective.
• Sensory analysis and coding influence what we experience.
• Sensory processing is localized in specific parts of the brain.
The visible spectrum is transduced by rods and cones in the retina leading to the construction of visual experience by the brain.
• The visible spectrum consists of electromagnetic radiation in a narrow range.
• The eyes and the brain form a complex system for sensing light. Vision is based on an active, computer-like analysis of light patterns.
• Four common visual defects are myopia (nearsightedness), hyperopia (farsightedness), presbyopia (loss of accommoda-tion), and astigmatism.
• The rods and cones are the eye’s photoreceptors in the retina.
• The rods specialize in peripheral vision, night vision, seeing black and white, and detecting movement.
• The cones, found exclusively in the fovea and otherwise toward the middle of the eye, specialize in color vision, acuity, and daylight vision.
Our ability to see colors is explained by the trichromatic theory (in the retina) and by the opponent-process theory (in the visual system beyond the eyes).
• The rods and cones differ in color sensitivity. Yellowish green is brightest for cones, blue-green for the rods (although they will see it as colorless).
• Total color blindness is rare, but 8 percent of males and 1 per-cent of females are red-green color-weak. Color weakness is a sex-linked trait carried on the X chromosome. The Ishihara test is used to detect color blindness and color weakness.
Attention Voluntarily focusing on a specific sensory input.
Interpretation Where pain is concerned, the meaning given to a stimulus.
Counterirritation Using mild pain to block more intense or long-lasting pain.
• Dark adaptation, an increase in sensitivity to light, is caused mainly by increased concentration of visual pigments in both the rods and the cones but mainly by rhodopsin recombining in the rods. Vitamin A deficiencies may cause night blindness.
Sound waves are transduced by the eardrum, auditory ossicles, oval window, cochlea, and ultimately, hair cells.
• Frequency theory explains how we hear tones up to 4,000 hertz; place theory explains tones above 4,000 hertz.
• Two basic types of hearing loss are conductive hearing loss and sensorineural hearing loss.
• Noise-induced hearing loss is a common form of sensorineural hearing loss caused by exposure to loud noise.
Olfaction (smell) and gustation (taste) are chemical senses responsive to airborne or liquefied molecules.
• It is also suspected that humans are sensitive to pheromones, although the evidence for this sense remains preliminary.
• The lock and key theory of olfaction partially explains smell.
In addition, the location of the olfactory receptors in the nose helps identify various scents.
• Sweet and bitter tastes are based on a lock-and-key coding of molecule shapes. Salty and sour tastes are triggered by a direct flow of ions into taste receptors.
The somesthetic senses include the skin senses, kinesthesis, and the vestibular senses.
• The skin senses are touch, pressure, pain, cold, and warmth.
Sensitivity to each is related to the number of receptors found in an area of skin.
• Distinctions can be made among various types of pain, includ-ing visceral pain, somatic pain, referred pain, warninclud-ing system pain, and reminding system pain.
• Various forms of motion sickness are related to messages received from the vestibular system, which detects gravity and movement.
• According to sensory conflict theory, motion sickness is caused by a mismatch of visual, kinesthetic, and vestibular sen-sations. Motion sickness can be avoided by minimizing sensory conflict.
Incoming sensations are affected by sensory adaptation (a reduction in the number of nerve impulses sent), by selective attention (selection and diversion of messages in the brain), and by sensory gating (block-ing or alteration of messages flow(block-ing toward the brain).
• Selective gating of pain messages apparently takes place in the spinal cord. Gate control theory proposes an explanation for many pain phenomena, except phantom limb pain.
Interactive Learning
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Pain can be reduced or controlled by altering factors that affect pain intensity.
• Pain is greatly affected by anxiety, control over the stimulus, attention, and the interpretation placed on an experience
• Pain can be reduced by controlling these factors through dis-traction, reinterpretation, counterirritation.
Web Resources
For an up-to-date list of direct links to interesting sites, including those listed here, visit the student companion site for this book at www.cengage.com/psychology/coon
Psychophysics Explore absolute and discrimination thresholds as well as other psychophysics phenomena.
The Joy of Visual Perception An online book about visual percep-tion, including information on the eye.
Virtual Tour of the Ear This site provides educational information about the ear and hearing and provides quick access to ear and hear-ing Web resources.
Taste and Smell Disorders Read about various disorders of taste and smell and what can be done about them.
American Pain Foundation Find out more about pain and its treatment.
© 2006 “Pintos” by Bev Doolittle®, courtesy of The Greenwich Workshop, Inc. www.greenwichworkshop.com
Gateway Questions
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In general, how do we construct our perceptions?•
Is perception altered by attention, motives, and emotions?•
What basic principles do we use to group sensations into meaningful patterns?•
What are perceptual constancies, and what is their role in perception?•
How is it possible to see depth and judge distance?•
What effect does learning have on perception?•
To what extent do we see what we expect to see?•
Is extrasensory perception possible?•
How can I learn to perceive events more accurately?Perceiving the World
Gateway Theme
We actively construct our perceptions out of the information provided by our senses and our past experience; the resulting perceptions are not always accurate representations of events.
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