Copyright © Allyn and Bacon 2007 Chapter 4 Sensation & Perception This multimedia product and its contents are protected under copyright law. The following.

Copyright © Allyn and Bacon 2007

Chapter 4Chapter 4

Sensation & Perception

This multimedia product and its contents are protected under copyright law. The following are prohibited by law:

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• ISBN: 0-131-73180-7


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


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?


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


TransductionTransduction

Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain


Sensory AdaptationSensory Adaptation

Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while


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)



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



Steven’s power law – S = kla

S = sensation

k = constant

l = stimulus intensity

a = a power exponent that depends on the sense being measured


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)


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


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?


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


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


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


Transduction of Light in the RetinaTransduction of Light in the Retina


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




Neural Pathways in the Human Visual Neural Pathways in the Human Visual SystemSystem


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


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


Color BlindnessColor Blindness


How the Visual System Creates How the Visual System Creates BrightnessBrightness

WavelengthWavelength

ColorColor

Intensity Intensity (amplitude)(amplitude)

BrightnessBrightness


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


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


How Sound Waves Become Auditory How Sound Waves Become Auditory SensationsSensations

Tympanic membrane –The eardrum



Cochlea –Where sound waves are transduced



Basilar membrane –Thin strip of tissue sensitive to vibrations

Cochlea



Auditory nerve –Neural pathway connecting the ear and the brain



Auditory cortex – Portion of the temporal lobe that processes sounds


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


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


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


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


SmellSmell


Taste buds –Receptors for taste (primarily on the upper side of the tongue)

TasteTaste

Gustation – The sense of taste


The Skin SensesThe Skin Senses

Touch

Warmth

Cold


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


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?


What is the RelationshipWhat is the RelationshipBetween PerceptionBetween Perception

and Sensation?and Sensation?

Percept – Meaningful product of a perception


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


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


Perceptual ConstanciesPerceptual Constancies

Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location


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


Perceptual IllusionsPerceptual Illusions

Do you see or ?


Perceptual IllusionsPerceptual Illusions

The Herman Grid

Do you see small gray squares between the black squares?


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


Cultural Influences on PerceptionCultural Influences on Perception

B

A

Which box is bigger, A or B?


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


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


The Gestalt Laws of Perceptual The Gestalt Laws of Perceptual GroupingGrouping

SimilaritySimilarity

ProximityProximity

ContinuityContinuity

Common fateCommon fate

PrägnanzPrägnanz


Law of PrägnanzLaw of Prägnanz

ABIRD

IN THETHE HAND


End of Chapter 4End of Chapter 4

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