Download - Human Development
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CHAPTER 4Sensation and Perception
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Learning Outcomes
• Define and differentiate between sensation and perception.
• Identify the parts of the eye, describe the properties of light and the theories of color vision.
Learning Outcomes
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Learning Outcomes
• Describe how visual perception is organized.
• Identify the parts of the ear; explain the sense of hearing.
Learning Outcomes
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Learning Outcomes
• Describe the chemical senses.
• Identify the skin senses and theoretical explanations for pain.
Learning Outcomes
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Learning Outcomes
• Describe the kinesthetic and vestibular senses.
• Explain why psychologists are skeptical about extrasensory perception.
Learning Outcomes
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SensationSensation and Perceptionand Perception
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What are Sensation and Perception?
• Sensation is the stimulation of sensory receptors and transmission of sensory information to the central nervous system.
• Perception is process by which sensations are organized and interpreted to form an inner representation of the world.
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Absolute Threshold
• Weakest amount of a stimulus that can be distinguished from no stimulus at all– Detected 50% of the time
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Subliminal Stimulation
• Sensory stimulation below a person’s absolute threshold for conscious perception (subliminal perception)– Lipton Ice (Experiment)
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Difference Threshold
• Minimum difference in magnitude of two stimuli required to tell them apart– Detected 50% of the time
• Weber’s constant– Fraction of the intensity by which a
source of physical energy must be increased or decreased so that a difference in intensity will be perceived.
• Just noticeable difference (jnd)– Minimum difference a person can detect
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Weber’s Constant
• Weber’s constant– Light – 2% of intensity– Weight – 2% of weight– Sound – one-third of 1% change in pitch
(frequency)– Taste – 20% difference in saltiness
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Signal-Detection Theory
• Stimulus characteristics and psychological factors interact to influence whether a stimulus is detected.– Psychological factors such as learning,
motivation, and psychological states
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Feature Detectors
• Neurons in the sensory cortex that first in response to specific features of sensory information such as lines or edges of objects– visual – respond to lines, color, textures,
movement– auditory – respond to pitch, loudness,
etc.
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Sensory Adaptation
The processes by which organisms become more sensitive to stimuli that are low in magnitude and less sensitive to stimuli that are constant or ongoing in magnitude
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Sensory Adaptation
• Sensitization– Positive adaptation – the type of sensory
adaptation in which we become more sensitive to stimuli that are low in magnitude
• Desensitization– Negative adaptation – the type of
sensory adaptation in which we become less sensitive to constant stimuli
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VisionVision
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Light
• Spectrum of electromagnetic energy– Vary in wavelength
•Within visible light, color is determined by wavelength
•Prism separates wavelengths
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The Visible Spectrum
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The Eye
• Light enters through a narrow opening– Cornea – transparent eye cover– Iris – muscle; colored part of the eye– Pupil – opening in the iris
•Sensitive to light and emotion
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The Eye
• Lens– Changes in thickness for focusing– Image is projected onto retina
• Light Sensitive Surface– Retina
•Photoreceptors –Rods, Cones, Bipolar and ganglion
cells
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The Eye
• Optic Nerve– Axons of ganglion neurons form optic
nerve– Conducts sensory input to brain (occipital
lobe)
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The Human Eye
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Rods and Cones
• Cones– Most densely packed in center of retina
(fovea)– Provide color vision
• Rods– Provide vision in black and white– More sensitive to dim light than cones
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Visual Acuity
• Sharpness of vision; greatest in the fovea• Blind spot
– Point in retina where ganglion cells converge• Nearsightedness
– See close objects most clearly – Elongated eyeball – Distant objects focus in front of retina
• Farsightedness– See distant objects most clearly – Eyeball is too short –
Images of nearby objects are focused behind the retina• Presbyopia
– A condition characterized by brittleness of the lens
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Light Adaptation
• Dark adaptation– Process of adjusting to lower lighting
•Cones reach maximum adaptation in about 10 minutes
•Rods continue to adapt up to 45 minutes
• Adaptation to bright light occurs within a minute or so
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Perceptual Dimensions of Color
• Hue (color)– Wavelength of light
• Value– Degree of brightness or darkness
• Saturation– Intensity of color
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Color Wheel
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Perceptual Dimensions of Color
• Color Wheel – Bend the colors of the spectrum into a
circle• Warm and Cool Colors
– Green-blue side of color wheel – cool– Yellow-orange-red side of color wheel –
warm
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Perceptual Dimensions of Color
• Complementary Colors– Colors across from one another on color
wheel– Mix complementary colors = gray
•Refers to light not pigments• Light is the source of all colors
– Pigments reflect and absorb light selectively
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Perceptual Dimensions of Color
• Afterimage– Persistent sensations of color are
followed by perception of the complementary color when the first color is removed
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Theories of Color
• Trichromatic Theory– the theory that color vision is made possible
by three types of cones, some of which respond to red light, some to green, and some to blue
• Opponent-Process Theory– the theory that color vision is made possible
by three types of cones, some of which respond to red or green light, some to blue or yellow, and some to the intensity of light•Cannot respond to both at simultaneously
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Color Blindness
• Trichromat– Normal color vision
• Monochromat– Totally color blind
• Dichromat– Partial color blindness– Discriminate between two colors – More common in males (sex linked trait)
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Plates from a Test for Color Blindness
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Visual Visual PerceptionPerception
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Visual Perception
• Process used to organize sensory impressions caused by the light that strikes our eyes
• Sensation is a mechanical process• Perception is an active process
– Involves experience, expectations and motivations
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Perceptual Organization
• Figure – Ground Perception– Ambiguous, unstable figures
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The Rubin Vase
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Gestalt Rules for Perceptual Organization
• Proximity– the perceptual tendency to group together
objects that are near one another• Similarity
– the perceptual tendency to group together objects that are similar in appearance
• Continuity– the tendency to perceive a series of points
or lines as having unity
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Gestalt Rules for Perceptual Organization
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Gestalt Rules for Perceptual Organization
• Common Fate– Elements moving together are grouped
together• Closure
– Perception of a complete figure, even when there are gaps in sensory information
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Top-Down Versus Bottom-Up Processing
• Top-Down Processing– Perception of the whole followed by
perception of the parts• Bottom-Up Processing
– Perception of the parts leads to perception of the whole
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Perceptual Constancies
• Acquired through experience; creates stability– Size Constancy
• the tendency to perceive an object as being the same size even as the size of its retinal image changes according to the object’s distance
– Color Constancy• the tendency to perceive an object as being
the same color even though lighting conditions change its appearance
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Perceptual Constancies
• Acquired through experience; creates stability– Brightness Constancy
• the tendency to perceive an object as being just as bright even though lighting conditions change its appearance
– Shape Constancy• the tendency to perceive an object as being
the same shape although the retinal image varies in shape as it rotates
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Visual Illusions
• Hering-Helmholtz Illusion– Perceive drawing as three-dimensional
• Müller-Lyer Illusion– Interpret length of lines based on
experience
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HearingHearing
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Sound
• Sound waves require a medium; air or water
• Sound waves compress and expand molecules of the medium, creating vibrations– A single cycle of compression and
expansion is one wave of sound• Human ear is sensitive to sound waves with
frequencies of 20 to 20,000 cycles per second
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Pitch and Loudness
• Pitch– Frequency (# of cycles per second)– Expressed in hertz (Hz)– Pitch of women’s voice is higher than
men’s• Loudness
– Height (amplitude) of sound waves– Expressed in decibels (dB)
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Sound Waves of Various Frequencies and Amplitudes
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Decibel Ratings of Familiar Sounds
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The Ear
• Shaped and structured to:– capture sound waves– vibrate in sympathy with them– transmit auditory information to the brain
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WHY DO WE HAVE TWO
EARS?
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Directional Stereophonic Hearing
• 3D Type of Hearing that we cannot experience if we only had one ear.
• In locating sound, Loudness and sequence in which sounds reach the ear provide cues; may turn head to clarify information
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The Human Ear
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Parts of the Ear
• Outer Ear– Funnels sound waves to the eardrum
• Middle Ear– Eardrum, hammer, anvil and stirrup– Acts as an amplifier– Oval window – Round window
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Parts of the Ear
• Inner Ear– Cochlea
•Basilar membrane•Organ of Corti
• Auditory nerve - the axon bundle that transmits neural impulses from the organ of Corti to the brain
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Locating Sounds
• Loudness and sequence in which sounds reach the ear provide cues– May turn head to clarify information
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Perception of Loudness and Pitch
• Related to number of receptor neurons on the organ of Corti– Sounds are perceived as louder when
more sensory neurons fire
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Perception of Loudness and Pitch
• Place theory– The theory that the pitch of a sound is
determined by the section of the basilar membrane that vibrates in response to the sound (Applies only to pitches at least 5,000 Hz)
• Frequency theory– the theory that the pitch of a sound is reflected in
the frequency of the neural impulses that are generated in response to the sound (20 to 1,000 Hz)
• Both theories work together
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Deafness
• Conductive deafness– Damage to middle ear– Hearing aids can help
• Sensorineural deafness– Damage to inner ear or auditory nerve– Cochlear implants may help with damage
to inner ear, but not auditory nerve
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The Chemical Senses:The Chemical Senses:Smell and TasteSmell and Taste
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Smell
• Odors trigger receptor neurons in olfactory membrane (the nerve that transmits information concerning odors from olfactory receptors to the brain)– Odors are sample molecules of
substances in the air• Sensory information about odors is sent to
the brain through the olfactory nerve• Odor contributes to flavor of foods
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Taste
• Taste is sensed through taste cells– Receptor neurons on taste buds
• Four primary taste qualities– Sweet, sour, salty and bitter– Umami (fifth basic taste) – savory
• Flavor of food depends on odor, texture, temperature and taste
• Individuals have taste sensitivities
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The Skin The Skin SensesSenses
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Touch and Pressure
• Skin sensory receptors fire when skin surface is touched– Active touching
• Some areas of the body are more sensitive– Nerve endings are more densely packed– More sensory cortex is devoted to
perception of sensations in those areas
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Temperature
• Receptors are located just beneath the skin– Skin temperature increases – receptors
for warmth fire– Skin temperature decreases – receptors
for cold fire• Sensations for temperature are relative
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Pain
• Nociceptors in skin are stimulated– Pain is usually sharpest where nerve
endings are densely packed– Pain can be felt deep within body– No nerve endings for pain in the brain
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Pain
• Prostaglandins– Facilitate transmission of pain message– Heighten circulation to injured area
(inflammation)– Pain-relieving drugs inhibit production of
prostaglandins– Emotional response and response to
stress affect degree of pain
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Phantom Limb Pain
• 2 out of 3 combat veterans with amputated limbs report phantom limb pain– May involve activation of nerves in the
stump of missing limb– May also involve reorganization of motor
and somatosensory cortex
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Gate Theory of Pain
• Nervous system can only process a limited amount of stimulation– Rubbing the pained area competes for
neural attention– Closes the “gate” on pain messages to
the brain
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Acupuncture
• Ancient Chinese method of pain control– Research shows it stimulates nerves to
the hypothalamus releasing endorphins– Endorphins are similar in structure and
effect to morphine
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Kinesthesis and the Kinesthesis and the Vestibular SenseVestibular Sense
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Kinesthesis
• Sense that informs you about the position and motion of your body– Sensory information is sent to the brain
from sensory organs in joints, tendons and muscles
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Vestibular System
• Housed mainly in semicircular canals in your ears
• Monitor your body’s motion and position in relation to gravity
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ESP: Is There Perception ESP: Is There Perception Without Sensation?Without Sensation?
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Extrasensory Perception - ESP
• Perception through means other than sensory organs– Precognition – Able to perceive future
events in advance– Psychokinesis – Mentally manipulating or
moving objects– Telepathy – Direct transmission of thought
or ideas from one person to another– Clairvoyance – Perception of objects that
do not stimulate sensory organs
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Existence of ESP
• Ganzfeld Procedure– Method for studying the existence of ESP
• No reliable evidence for existence of ESP