5 th edition copyright © prentice hall 20073-1 psychology stephen f. davis emporia state university...

Copyright © Prentice Hall 2007 3-1

5th Edition

PsychologyStephen F. Davis

Emporia State University Joseph J. Palladino

University of Southern IndianaPowerPoint Presentation by

Cynthia K. Shinabarger ReedTarrant County College

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5th Edition

Sensation and Perception

Chapter 3


Sensation, Perception, and Psychophysics

• Sensation is the activation of receptors by stimuli in the environment.

• Sensations are the basic building blocks of perception.

• Perception is the process of organizing and attempting to understand the sensory stimulation we receive.



• To activate a particular receptor, a specific type of energy must be present—light waves for vision, movement of air molecules for hearing, molecules in a liquid solution for taste, and so forth.



• Transduction is the process by which the receptors change the energy they receive into a form that can be used by the nervous system.

• Adaptation occurs when continued presentation of the same stimulus results in a loss of sensitivity to that stimulus.



• Psychophysicists, such as Ernst Weber and Gustav Fechner, studied the relationship between the mind and the body.

• Weber’s law is the observation that the amount of stimulus increase or decrease required to notice a change, divided by the original stimulation, is a constant.



• The just noticeable difference (jnd) is the smallest difference between two stimuli that is noticeable 50% of the time by participants.



• Gustav Fechner studied both the absolute threshold and the differential threshold.

• The absolute threshold is the minimum amount of energy required for conscious detection of a stimulus 50% of the time by participants.



• To determine the differential threshold or jnd, we investigate the amount of stimulus energy that must be added to or subtracted from an existing stimulus for a participant to notice a difference (that is, to produce a just noticeable difference) 50% of the time.



• Signal detection theory, or the contention that the threshold varies with the nature of the signal and noise, was developed to explain the difficulties one might encounter in distinguishing a certain stimulus from the background or noise.



• Subliminal stimuli are stimuli that are below the threshold of consciousness.

• Although a limited number of presentations of a subliminal stimulus may not alter our behaviors dramatically and immediately, there is some evidence that repeated subliminal presentations may change our attitudes and opinions.


Sensory Systems

• Vision is a process that involves the reception of electromagnetic waves by visual receptor cells.

• This kind of energy travels in waves that vary greatly in length.

• We measure wavelengths, or the length of waves, in nanometers (nm), which are billionths of a meter.

• The only light waves that humans can detect have wavelengths between approximately 380 and 760 nm.


Sensory Systems

• This limited range of stimuli (the human eye can see only a small portion of the spectrum) is called the visible spectrum.

• Different light wavelengths are associated with different colors.

• Amplitude refers to the strength or intensity (brightness) of the light.


Sensory Systems

• Saturation refers to the “trueness” or purity of the colors we perceive.

• With radiant light, visible energy is emitted (released) directly by an object.

• With reflected light, by contrast, energy is reflected by objects.


Sensory Systems

• If a surface reflects only one wavelength, the color you perceive is pure.

• The degree of purity decreases as the number of different, reflected wavelengths increases.


Sensory Systems

• Vision involves a complex chain of events.

• Initially, light waves pass through the protective cornea.

• In addition to its protective function, the cornea helps focus the light waves.


Sensory Systems

• After striking the cornea, light waves enter an open area called the anterior chamber.

• Here they pass through the aqueous humor, a clear watery fluid.

• Then the light waves are funneled through the small opening known as the pupil.


Sensory Systems

• The pupil is surrounded by a colored membrane, the iris, which changes shape (like the diaphragm of a camera) to regulate the size of the pupil and therefore the amount of light taken in.

• Next, the light passes through the lens.


Sensory Systems

• The lens, which is supported by two powerful ciliary muscles, is elastic; it can change shape to focus the visual image.

• Changing the shape of the lens to focus is known as accommodation.


Sensory Systems

• After passing through the lens, the light waves enter a second, larger open space called the posterior chamber.

• Finally, the light waves strike the retina, the light-sensitive tissue at the back of the eye that contains the visual receptors (rods and cones).


Sensory Systems

• The retina is made up of several layers: the three major layers are the ganglion cell layer, the bipolar cell layer, and the photoreceptor layer.

• After light strikes the surface of the retina, it must travel through several layers of cells before it activates the visual receptors, which make up the back layer of the retina.


Structures of the Eye


Sensory Systems

• Light waves cause the receptors to change their electrical charge.

• If that change is great enough, the bipolar cells fire.

• If enough bipolar cells fire, the next layer of cells, the ganglion cells, fires.


Layers of Cells in the Retina


Sensory Systems

• The axons of the ganglion cells come together to form the optic nerve, which carries visual information to higher brain centers.

• At the point where the axons of the ganglion cells come together and leave the eyeball, there are no receptors.

• This area is known as the blind spot.


Sensory Systems

• The optic nerves from each eye join at the optic chiasm, which is located on the underside of the brain, just in front of the pituitary gland.

• The fibers from the nasal half (closest to the nose) of the retina cross to the opposite hemisphere; those from the peripheral (outlying) half of each retina continue to the hemisphere on the same side of the body.


Sensory Systems

• The next stop is an area in the thalamus, the relay station in the forebrain.

• Ultimately, the visual information is received by the occipital lobe of the cortex, where higher-level visual processing begins.


The Visual Pathway


Sensory Systems

• The rods (120 to 125 million per eye) are the most prevalent visual receptors.

• They have a lower threshold and lower acuity (sharpness of perception) than cones and do not detect color.

• By contrast, the cones (6 to 7 million) are less prevalent, have a higher threshold and higher acuity, and are able to detect color.


Sensory Systems

• The rods are slender and cylindrical, whereas the cones are much broader.

• Most of the cones are found in one area, the fovea, an indented spot in the center of the retina. Both the rods and cones contain light-sensitive chemicals called photopigments.

• When light strikes the rods and cones, it causes a chemical reaction in these photopigments.


Sensory Systems

• Two theories of color vision have been formulated.

• The trichromatic theory proposes that there are three different types of color receptors.


Sensory Systems

• The opponent-process theory stresses the pairing of color experiences; activation of one process can inhibit its partner.

• Both theories are supported by research findings.

• Opponent-process cells may also be responsible for the production of color afterimages.

• A color afterimage is the perception of a color that is not really present; it occurs after viewing the opposite or complementary color.


Sensory Systems

• People who suffer deficits in color vision are said to be color deficient.

• Monochromats are unable to see color.

• Dichromats lack the ability to see one of the three primary colors (red, blue, or green).


Sensory Systems

• Audition is the sense of hearing.

• Just as we see light waves, we hear sound waves.

• A sound wave is essentially moving air.

• Like light waves, sound waves have three distinct characteristics: wavelength (frequency), amplitude (intensity), and purity (also known as timbre).


Sound Waves


Sensory Systems

• Frequency is measured in cycles per second and expressed in hertz (Hz).

• As with light waves, the amplitude, or height, of the sound wave affects its intensity.

• Greater amplitude results in a more intense sound.

• The amplitude of sound waves is measured in decibels (db).


Sensory Systems

• Decibel levels represent the amount of energy producing the pressure of the vibrations we perceive as sound; the greater the pressure, the stronger or more intense the vibration.

• The purity or timbre of a sound wave can be measured, but we do not experience many pure tones in our lifetimes.


Sensory Systems

• Like the visual receptors, the auditory receptors are sensitive to a limited range of sound waves.

• Basically, we hear sounds with wavelengths between 20 and 20,000 Hz.

• Our hearing is more acute at 1,000 Hz; greater intensity (amplitude) is required if we are to hear tones at lower and higher frequencies.


Sensory Systems

• The auditory system is divided into three components: the outer ear, the middle ear, and the inner ear.

• The outer ear, especially the pinna, gathers sound waves and starts them on their way to the auditory receptors.

• The sound waves are then funneled down the auditory canal.

• Ultimately they strike the eardrum and cause it to move.


Sensory Systems

• Movement of the eardrum in turn causes the three bones (hammer, anvil, and stirrup) of the middle ear, collectively called the ossicles, to vibrate.

• The hammer (malleus), which is attached to the eardrum, strikes the anvil (incus).

• The anvil in turn strikes the stirrup (stapes).


Sensory Systems

• The stirrup is connected to the oval window, which connects the middle ear to the snail-shaped cochlea of the inner ear.

• When the stirrup causes the oval window to vibrate, fluid located in the cochlea is set in motion.

• The motion of the fluid produces vibration in the basilar membrane.

• This vibration in turn causes the organ of Corti, which rests on it, to rise and fall.


Sensory Systems

• When the organ of Corti moves upward, the hair cells that project from it brush against the tectorial membrane located above it.

• The hair cells are the auditory receptors where transduction occurs.

• Contact with the tectorial membrane causes them to bend; when they bend, they depolarize.


Sensory Systems

• Sufficient depolarization of the auditory receptors causes the neurons that synapse with them to fire.

• The axons of these neurons come together before they leave the cochlea to form the auditory nerve, which transmits auditory information to higher brain centers.


Sensory Systems

• From the cochlea, the auditory nerve travels to the medulla, where some fibers cross to the opposite hemisphere.

• The next stop is the thalamus.

• Ultimately the information reaches the temporal lobe of the cortex for processing.


The Auditory System


Sensory Systems

• At present, there are two theories to explain how we hear different tones or pitches.

• The older place theory, proposed by Hermann von Helmholtz in 1863, says that hair cells located at different places on the organ of Corti transmit information about different pitches.


Sensory Systems

• The place theory says that what you hear depends on which hair cells are activated.

• For this theory to be correct, the basilar membrane has to vibrate in an uneven manner, which is exactly what happens with frequencies above 1,000 Hz.


Sensory Systems

• The frequency theory of Ernest Rutherford applies to frequencies below 1,000 Hz.

• In 1886, Rutherford suggested that we perceive pitch according to how rapidly the basilar membrane vibrates.

• The faster the vibration, the higher the pitch, and vice versa.

• The frequency theory works fine with frequencies up to 100 Hz; typically, however, neurons do not fire more than 100 times per second.


Sensory Systems

• According to the volley principle, at frequencies above 100 Hz auditory neurons do not all fire at once; instead, they fire in rotation or in volleys.

• Two mechanisms help us locate the source of a sound.

• The first is blockage of certain sounds by the head.

• The second mechanism is time delay in neural processing.


Sensory Systems

• Several hearing problems have been studied extensively: conduction deafness, sensorineural deafness, and central deafness.

• The first two may be caused by exposure to very loud noises.

• Conduction deafness refers to problems associated with conducting or transmitting sounds through the outer and middle ears.


Sensory Systems

• In addition to excessive exposure to loud noises that can cause the eardrum to burst, common causes of conduction deafness are excessive ear wax or damage to the hammer, anvil, or stirrup.

• Sensorineural deafness is caused by damage to the inner ear, especially the hair cells.

• Central deafness is caused by disease and tumors in the auditory pathways and auditory cortex of the brain.


Sensory Systems

• Gustation refers to the sense of taste.• The stimuli for taste are molecules dissolved in a

liquid. • Once molecules are in solution, they can come

into contact with the taste receptor cells, which are located in structures known as taste buds.

• Each taste bud contains between 50 and 100 taste receptors.

• The taste buds line the walls of small bumps on the tongue and throat called papillae.


Sensory Systems

• Individual taste receptor cells do not last forever; with a life expectancy of only 10 days to 2 weeks, the cells within a taste bud are continually being replaced.

• The number of taste buds increases during childhood to a maximum of about 10,000.

• At approximately age 40 the trend reverses and our sense of taste declines.


Sensory Systems

• Although researchers are not absolutely sure how taste receptors work, the most credible theories advanced to date suggest that molecules in the solution attach to or fit into receptor sites.

• The actual taste receptor sites are located on microscopic hairs, known as microvilli, that project from the tips of the taste receptor cells.


Sensory Systems

• The receptor sites have different geometric shapes or different types of ion channels, so the shape of the molecule determines whether it fits into a specific receptor site.

• For nearly a century, researchers have agreed with the proposal that we are sensitive to at least four primary tastes: sweet, sour, bitter, and salty.


Sensory Systems

• In the late 1990s, receptor sites for a fifth taste, umam (savory or meaty), were identified; however, researchers are not in complete agreement that umami really is a separate taste.

• Hence it is reasonable to suppose that there are at least four different types (shapes) of receptor sites.

• Once the sites are occupied, depolarization occurs and information is transmitted through the gustatory nerve to the brain.


Sensory Systems

• The gustatory nerve goes from the taste buds to the medulla in the hindbrain, where they synapse.

• From there the information travels to the thalamus and is then relayed to the somatosensory cortex in the forebrain.

• At this point, you are able to determine the nature of the taste you have experienced.


Sensory Systems

• Olfaction refers to the sense of smell.• Odors are produced by molecules in the air. • More than 2 million Americans have a significant

loss in the ability to smell. • This condition, called anosmia, can result from

genetic defects, aging, viruses, allergies, or certain prescription drugs.

• The most common cause, however, is head trauma, which can shear off axons that run from the olfactory nerves to the brain.


Sensory Systems

• The nose does not contain the olfactory receptors; its function is to collect and filter the air we breathe.

• The olfactory receptors are located in an area of tissue of about 2.5 cm (1 in.) square in each nasal cavity.

• We have about 10 million olfactory receptors, each of which has 6 to 12 hair-like projections called cilia.


Sensory Systems

• Like taste receptors, olfactory receptors are continually dying and being replaced.

• The life span of an olfactory receptor is about 5 to 8 weeks.

• There may be as many as 1,000 different types of olfactory receptor sites.

• Although researchers do not know a great deal about how they work, the olfactory receptors appear to operate under the same type of lock-and-key/pattern recognition principle as the taste receptors.


Sensory Systems

• The olfactory nerve takes a somewhat different route to the brain from the other senses.

• The first step is a synapse in the olfactory bulb, which is located near the optic chiasm on the underside of the brain.

• From there, some of the olfactory nerve fibers go to the amygdala.

• From the amygdala, the olfactory nerve travels to the thalamus and hypothalamus and then on to the cerebral cortex for higher-level processing.


Olfaction


Sensory Systems

• One set of researchers reported the results of an experiment that proved the interdependence of smell and taste in experiencing a flavor.

• In this study they placed a drop of a certain flavor on a participant’s tongue and asked the person to identify the taste.

• When participants could smell normally, they were correct on most tries; when the experimenter prevented them from smelling, however, they were often unable to identify it.


Sensory Systems

• The vestibular sense, which originates in the inner ear, provides information about the body’s orientation and movement.

• The vestibular system consists of the three semicircular canals in the inner ear and the utricle.

• The semicircular canals are located at right angles to each other to provide information about movement in all directions.


Sensory Systems

• Each semicircular canal is filled with a jellylike fluid that moves as the head moves.

• Movement of the fluid in the canal causes hair cells located in the canal to bend.

• Bending the hair cells sends information about movement to the brain.

• The utricle, a fluid-filled chamber also located in the inner ear, operates on the same principle as the semicircular canals and serves as a gravity detector.


Sensory Systems

• The kinesthetic sense is a system of receptors located in the muscles and joints that provides information about the location of the extremities.

• Sense receptors located in the joints and muscles send information to the brain concerning muscle tension and joint position.

• The brain combines this information with other sensory input, such as vision and audition, to help you determine the location of your limbs.


Sensory Systems

• Cutaneous senses refers to a system of receptors located in the skin that provides information about touch, pressure, pain, and temperature.


Sensory Systems

• The wide variety of skin receptors for touch or pressure are called mechanoreceptors; the receptors for temperature are called thermoreceptors.

• The general term for receptors that respond to painful stimuli is nocioreceptors.


Sensory Systems

• One theory of pain, the gate control theory, has greatly influenced our understanding of pain. According to this theory, pain impulses are transmitted from the receptors (free nerve endings) to the spinal cord.

• The axons of the pain neurons release substance P in the spinal cord.

• In turn, substance P causes neurons in the spinal cord to send information about pain to the brain for processing and perception.


Sensory Systems

• Thus the painful stimulus, in conjunction with substance P, opens the pain gate.

• Neurons that descend from the brain to the spinal cord release opioid peptides called endorphins.

• In turn, the endorphins block the release of substance P and the pain gate is closed.


Perception

• We do not perceive everything in our environment; our motives greatly influence our perceptions.

• Similarly, certain stimuli are more likely than others to attract our attention.

• In dichotic listening experiments, a different message is presented to each of a participant’s ears, and the participant is asked to recall both messages.


Perception

• Dichotic listening tasks are designed to study divided attention, the ability to attend to more than one message or type of information at the same time.

• Research in this area has uncovered some intriguing information about human perception.

• For example, we hear (and understand) much more than the information of which we are consciously aware as illustrated by the “cocktail-party phenomenon.”


Perception

• In addition to needs, motives, and prejudices, certain aspects of stimuli determine which ones get our attention.

• For example, people generally pay more attention to stimuli that are larger, louder, or more colorful than others.

• When something happens unexpectedly, our attention is attracted very quickly.

• When contrast and surprise combine, our attention is commanded even more quickly.


Perception

• The ability to discriminate among shapes and figures is known as pattern perception.

• The feature analysis theory states that we perceive the elements of an object and then combine them to produce our perception of the object (bottom-up processing).

• Research suggests that, at least in some instances, we use a top-down approach in which the whole object is recognized before its component parts are identified.


Perception

• Perceptual constancy is the tendency to perceive the size and shape of an object as constant even though its retinal image changes.

• Shape constancy means that your perception of the shape of an object as viewed from different angles does not change even though the image projected on your retina does so.


Perception

• Size constancy is the tendency to perceive the size of an object as constant despite changes in its retinal image.

• Depth perception is the ability to perceive our world three-dimensionally.

• Two main types of cues, binocular and monocular, are used to create our perception of depth.


Perception

• Binocular cues require the integrated use of both eyes, whereas monocular cues are effectively processed using information from only one eye.

• Two binocular cues are adjustments of the eye muscles (a weak/nonprecise cue) and binocular disparity.


Perception

• If you open and close one eye and then the other, it is obvious that you do not see exactly the same thing with each eye.

• The closer the object, the greater the difference between what the two eyes see.

• This difference occurs because each eye sees from a different angle, a phenomenon known as binocular disparity.

• When the images from both eyes merge in the brain, a sense of depth is created.


Perception

• Monocular cues of depth include– interposition (near objects partially obscure

more distant objects), – texture gradient (the texture of a surface

becomes smoother with increasing distance), – linear perspective (parallel lines appear to

converge as they recede into the distance), and

– relative brightness (brighter objects appear closer than duller-appearing ones).


Perception

• The Gestalt psychologists demonstrated that we actively organize our perceptual world into meaningful groups or wholes.

• Figure–ground relation is the organization of perceptual elements into a figure (the focus of attention) and a background.


Perception

• Several conditions promote the grouping of perceptual elements.

• With proximity, items that are close to each other are perceived as a group.

• According to the Gestalt principle of similarity, items that are alike are grouped together: XXXOOO, is perceived as three Xs and three Os.


Perception

• The Gestalt principle of good continuation says that we perceive continuous, flowing lines more easily than choppy or broken lines.

• The Gestalt principle of closure says that organizing our perceptions into complete objects is easier than perceiving each part separately.


Perception

• Apparent motion is the illusion of movement in a stationary object.

• Perceptual hypotheses are inferences about the nature of stimuli received from the environment.

• Perceptual illusions are misperceptions or interpretations of stimuli that do not correspond to the sensations received.


Perception

• Recent advances in the study of brain functioning promise to change our conception of sensory processes and perception.

• For example, studies of the human visual cortex indicate that sensory processing does not occur in a strictly sequential manner where one part of the brain performs an activity and then passes the modified sensation on to another brain area for additional processing.


Perception

• The picture that emerges is of a parallel processing system in which information simultaneously flows both from lower to higher levels and from higher to lower levels in the brain.

• For example, exciting breakthroughs also are occurring in the study of higher-level, more cognitive processes, such as visual search.


Perception

• Visual search is the process of identifying the presence or absence of a target stimulus among a group of distractor items.

• Research on this topic shows that when stimuli have high salience (that is, when they are relevant, meaningful, or distinctive), visual search is done efficiently, rapidly, and in a parallel manner.

• Indeed, such high-salience stimuli seem to “pop out” from the distractors.


Perception

• Perception may be influenced by the social context.

• For example, the Ebbinghaus illusion is influenced by the type of social stimuli used.


Paranormal Phenomena

• Extrasensory perception (ESP) refers to behaviors or experiences that cannot be explained by information received from the senses.

• The term ESP is reserved for paranormal phenomena that do not involve the senses.

• The most frequently mentioned examples of ESP are clairvoyance, telepathy, and precognition.



• Clairvoyance is the claimed ability to “see” information from objects or events without direct contact with the senses.

• Telepathy is the claimed ability to perceive the thoughts or emotions of others without the use of recognized senses.

• Precognition is knowledge of a future event or circumstance obtained by paranormal means.



• Psychokinesis (once known as telekinesis) is the claimed power of the mind to influence matter directly.

• Because psychokinesis does not involve perception, some researchers do not consider it an example of ESP.

• The term parapsychology is often used to refer to “the study of paranormal phenomena, which are considered to be well outside the bounds of established science.”



• The claims offered by supporters of ESP are sometimes presented in ways that make designing a definitive test difficult, if not impossible.

• Most scientists agree that allegedly paranormal phenomena can be explained without resort to non-normal evidence.



• Many people have psychic experiences, or at least experiences they interpret as such.

• Psychologists suggest that paranormal experiences are an inevitable consequence of the way we perceive and remember information.

• We can be fooled by our experiences in much the same way we are fooled by the visual illusions described earlier.



• Although the methods of studying paranormal phenomena have improved, “the goal of a conclusively convincing demonstration or a repeatable experiment has not been achieved.”

• Should we therefore dismiss even the possibility of paranormal phenomena?



• Before we do, let’s consider an important history lesson: some phenomena that in the past were considered to be paranormal, impossible, or even fraudulent have since been verified to be real.

5 th edition copyright © prentice hall 20073-1 psychology stephen f. davis emporia state university...

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