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Chapter 4Chapter 4
Sensation & Perception
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Sensation and PerceptionSensation and Perception
Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it – either inside or outside the body
Perception –A process that makes sensory patterns meaningful and more elaborate
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The brain senses the world indirectly because the sense organs convert stimulation
into the language of the nervous system: neural
impulses
How Does StimulationHow Does StimulationBecome Sensation?Become Sensation?
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TransductionTransduction
Transduction – Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses
Receptors –Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse
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TransductionTransduction
Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain
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Sensory AdaptationSensory Adaptation
Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while
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ThresholdsThresholds
Absolute threshold – Amount of stimulation necessary for a stimulus to be detected
Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)
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ThresholdsThresholds
Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low
Fechner’s law – S = k log RS = sensation
R = stimulus
k = constant that differs for each sensory modality
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ThresholdsThresholds
Steven’s power law – S = kla
S = sensation
k = constant
l = stimulus intensity
a = a power exponent that depends on the sense being measured
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Signal Detection TheorySignal Detection Theory
Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes
Stimulus eventStimulus event
Neural activityNeural activity
Comparison with Comparison with personal standardpersonal standard
Action (or no action)Action (or no action)
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Subliminal PersuasionSubliminal Persuasion
Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses
No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits
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The senses all operate in much the same way, but each extracts different information
and sends it to its own specialized processing region
in the brain
How Are the Senses Alike? How Are the Senses Alike? How Are They Different?How Are They Different?
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The Anatomy of Visual SensationThe Anatomy of Visual Sensation
Fovea – Area of sharpest vision in the retina
Retina – Light-sensitive layer at the back of the eyeball
Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses
Rods – Sensitive to dimlight but not colors
Cones – Sensitive tocolors but not dim light
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The Anatomy of Visual SensationThe Anatomy of Visual SensationOptic nerve –
Bundle of neurons that carries visual information from the retina to the brain
Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors
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Color –Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world
The Anatomy of Visual SensationThe Anatomy of Visual Sensation
Visual cortex –Part of the brain – the occipital cortex – where visual sensations are processed
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Transduction of Light in the RetinaTransduction of Light in the Retina
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AfterimagesAfterimages
Afterimages – Sensations that linger after the stimulus is removed
In the following slide, fix your eyes on the dot in the center of the flag
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Neural Pathways in the Human Visual Neural Pathways in the Human Visual SystemSystem
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How the Visual System Creates ColorHow the Visual System Creates Color
Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light
Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive
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Brightness – Sensation caused by the intensity of light waves
How the Visual System Creates ColorHow the Visual System Creates Color
Color blindness – Vision disorder that prevents an individual from discriminating certain colors
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Color BlindnessColor Blindness
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How the Visual System Creates How the Visual System Creates BrightnessBrightness
WavelengthWavelength
ColorColor
Intensity Intensity (amplitude)(amplitude)
BrightnessBrightness
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Hearing: If a Tree Falls in the Hearing: If a Tree Falls in the Forest...Forest...
The Physics of SoundFrequency –
Number of cycles completed by a wave in a given amount of time
Low Frequency High Frequency
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Hearing: If a Tree Falls in the Hearing: If a Tree Falls in the Forest...Forest...
The Physics of Sound
High Amplitude Low Amplitude
Amplitude – Physical strength of a wave
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How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations
Tympanic membrane –The eardrum
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How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations
Cochlea –Where sound waves are transduced
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How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations
Basilar membrane –Thin strip of tissue sensitive to vibrations
Cochlea
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How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations
Auditory nerve –Neural pathway connecting the ear and the brain
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How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations
Auditory cortex – Portion of the temporal lobe that processes sounds
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The Psychology of Pitch,The Psychology of Pitch,Loudness, and TimbreLoudness, and Timbre
Pitch – Sensory characteristic of sound produced by the frequency of the sound wave
Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave
Timbre – Quality of a sound wave that derives from the wave’s complexity
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DeafnessDeafness
Conduction deafness –An inability to hear resulting from damage to structures of the middle or inner ear
Nerve deafness –An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers
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Position and MovementPosition and Movement
Vestibular sense –Sense of body orientation with respect to gravity
Kinesthetic sense –Sense of body position and movement of body parts relative to each other
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SmellSmell
Olfaction –Sense of smell
Olfactory bulbs –Brain sites of olfactory processing
Pheromones –Chemical signals released by organisms to communicate with other members of the species
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SmellSmell
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Taste buds –Receptors for taste (primarily on the upper side of the tongue)
TasteTaste
Gustation – The sense of taste
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The Skin SensesThe Skin Senses
Touch
Warmth
Cold
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PainPain
Placebos –Substances that appear to be drugs but are not
Placebo effect –A response to a placebo caused by subjects’ belief that they are taking real drugs
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Perception brings meaning to sensation, so perception
produces an interpretation of the external world, not a
perfect representation of it
What is the RelationshipWhat is the RelationshipBetween PerceptionBetween Perception
and Sensation?and Sensation?
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What is the RelationshipWhat is the RelationshipBetween PerceptionBetween Perception
and Sensation?and Sensation?
Percept – Meaningful product of a perception
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The Machinery ofThe Machinery ofPerceptual ProcessingPerceptual Processing
Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus
Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept
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Bottom-Up andBottom-Up andTop-Down ProcessingTop-Down Processing
Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts
Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors
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Perceptual ConstanciesPerceptual Constancies
Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location
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Perceptual Ambiguity and DistortionPerceptual Ambiguity and Distortion
Illusions – Demonstrably incorrect experience of a stimulus pattern, shared by others in the same perceptual environment
Ambiguous figures – Images that are capable of more than one interpretation
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Perceptual IllusionsPerceptual Illusions
Do you see or ?
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Perceptual IllusionsPerceptual Illusions
The Herman Grid
Do you see small gray squares between the black squares?
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Theoretical Explanations for Theoretical Explanations for PerceptionPerception
Learning-based inference –View that perception is primarily shaped by learning, rather than innate factors
Perceptual set –Readiness to detect a particular stimulus in a given context
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Cultural Influences on PerceptionCultural Influences on Perception
B
A
Which box is bigger, A or B?
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The Gestalt ApproachThe Gestalt Approach
Gestalt psychology – View that much of perception is shaped by innate factors built into the brain
Figure – Part of a pattern that commands attention
Ground – Part of a pattern that does not command attention; the background
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Closure – Tendency to fill in gaps in figures and see incomplete figures as complete
The Gestalt ApproachThe Gestalt Approach
Subjective contours – Boundaries that are perceived but do not appear in the stimulus pattern
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The Gestalt Laws of Perceptual The Gestalt Laws of Perceptual GroupingGrouping
SimilaritySimilarity
ProximityProximity
ContinuityContinuity
Common fateCommon fate
PrägnanzPrägnanz
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Law of PrägnanzLaw of Prägnanz
ABIRD
IN THETHE HAND
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End of Chapter 4End of Chapter 4