psy i: winter '16: chpt. 3 lecture

mastering the world ofpsychology

CHAPTER

fifth edition

Copyright © 2014, © 2011, © 2008 by Pearson Education, Inc.All Rights Reserved

Sensation and Perception

3

Mastering the World of Psychology, Fifth EditionSamuel Wood | Ellen Green Wood | Denise Boyd

Learning Objectives

3.1 What are the absolute and difference thresholds?

3.2 How does transduction change sensory information?

3.3 How does each part of the eye function in vision?

3.4 How does visual information get from the retina to the primary visual cortex?

3.5 How does color vision work?3.6 What are the physical characteristics of

sound?


Learning Objectives

3.7 How does each part of the ear function in hearing?

3.8 How do the kinesthetic and vestibular senses help us move and stay balanced?

3.9 How do smell sensations get from the nose to the brain?

3.10 How do we detect the primary taste sensations?

3.11 How does the skin provide pleasant and unpleasant sensations?


Learning Objectives

3.12 What do we gain and lose when we attend to a stimulus?

3.13 How does prior knowledge influence perception?

3.14 How do we perceive social stimuli?3.15 What are the Gestalt principles of perceptual

organization?3.16 What do monocular and binocular cues

contribute to perception?


Learning Objectives

3.17 How does the brain perceive motion? 3.18 What are three puzzling perceptions?3.19 What do studies of subliminal perception, ESP

and synesthesis show?


Overview

• The Process of Sensation• Vision• Hearing and Balance• Smell, Taste, and Touch• Influences on Perception• Principles of Perception• Unusual Perceptual Experiences


The Process of Sensation

• Sensation– process whereby senses pick up visual,

auditory, and other sensory stimuli – transmits this stimuli to the brain– is the "raw" material


The Process of Sensation

• Perception – process whereby the brain actively

organizes and interprets sensory information

– provides the "finished" product


The Process of Sensation:Absolute and Difference Thresholds• What is the softest sound you can hear

—the dimmest light you can see—the most diluted substance you can taste?– Experiments answer these questions.– Measures of the minimal perceptible

amount for the senses are known as absolute thresholds.

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FIGURE 3.1 Absolute ThresholdsJust as the threshold of a doorway is the dividing point between being outside a room and being inside it, the absolute threshold of a sense marks the difference between not being able to perceive a stimulus and being just barely able to perceive it.


The Process of Sensation:Absolute Threshold

• Marks the difference between not being able to perceive a stimulus and being just barely able to perceive the stimulus

• Minimum amount of sensory stimulation detected 50 percent of the time

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The Process of Sensation:Difference Threshold

• Difference Threshold– a measure of the smallest increase or

decrease in a physical stimulus required to produce the just noticeable difference

• Just Noticeable Difference (JND) – the smallest change in sensation a

person is able to detect 50 percent of the time

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The Process of Sensation:Weber's Law

• JND depends on a percentage of change in a stimulus rather than on a fixed amount of change.

• Weber's Law – percent of change necessary for

detection

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• Examples– Weight must increase or decrease by 2

percent to allow a subject to notice the difference.

– In music, difference is noted in a tone change higher or lower in pitch by 0.33 percent.

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• Weber's law best applies to:– People with average sensitivities – Sensory stimuli that are neither very

strong nor very weak

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The Process of Sensation:Sensory Receptors and Transduction• Sensory Receptors

– highly specialized cells in the sense organs

– detect and respond to one type of sensory stimuli

– transduce (convert) stimuli into neural impulses

– provide the link between the physical sensory world and the brain

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The Process of Sensation:Sensory Receptors and Transduction• Transduction

– process by which sensory receptors convert sensory stimulation into neural impulses

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The Process of Sensation:Sensory Adaptation

• Process whereby sensory receptors grow accustomed to constant, unchanging levels of stimuli over time

• Not likely to occur in the presence of a very strong stimulus

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FIGURE 3.2 The ElectromagneticSpectrum Human eyes can perceive only a very thin band of electromagnetic waves, known as the visible spectrum.


Vision

• Eyes respond only to visible light waves.– Waves form a small subgroup of

electromagnetic waves called the visible spectrum.

• Electromagnetic waves are measured in wavelengths.– the distance from the peak of a light

wave to the peak of the next wave

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FIGURE 3.3 The Major Parts of the Human Eye


VisionThe Eye: Process of Sight

• The cornea performs the first step.– bends light rays inward– directs the light rays through the pupil

• The iris contracts and dilates the pupil to regulate the amount of light entering the eye.

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VisionThe Eye: Process of Sight

• The lens focuses on viewed objects, directs images to the retina.– Accommodation: flattening and bulging

action of lens– presbyopia: age-related loss of lens'

ability to change shape• The image projected onto the retina is

upside down and reversed from left to right.

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FIGURE 3.4 From Retinal Image to Meaningful InformationBecause of the way the lens alters light rays in order to produce a clear image, images are upside down on the retina. The brain’s visual processing system takes the upside-down retinal image and flips it so it is properly orientated.


VisionThe Eye: Rods and Cones

• Light-sensitive receptor cells located at the back of the retina

• There are 120 million rods and 6 million cones in each retina.

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• Rhodopsin in the rods enables adaptation to light.– two components

opsin and retinal– light adaptation

opsin and retinal break apart

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• Rhodopsin in the rods enables adaptation to light.– dark adaptation

opsin and retinal bond, forming rhodopsin

– fovea contains only cones; involved in clear,

sharp vision

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Vision:Vision and the Brain

• Light passes through 4 layers of tissue after reaching the rods and cones.

• Each layer contains specialized neurons.– include ganglion, amacrine, bipolar, and

horizontal cells

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• Axon-like extensions of ganglion cells are bundled together in a pencil-sized cable exiting the retina.– blind spot

no rods or cones present located where the ganglion cable exits

the retina

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FIGURE 3.3 The Major Parts of the Human Eye



• Bundled ganglion cells form the optic nerve.

• Optic Chiasm– point where some optic nerve fibers

cross to opposite side of brain– crossing over allows the image to be

projected to both hemispheres of brain

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• Nerve fibers extend from the optic chiasm to the thalamus, transmit impulses to the primary visual cortex.

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• Feature Detectors– are neurons of the primary visual cortex – respond only to specific visual patterns

(for example, to lines or angles)– coded at birth to make their unique

responses

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Major Structures of the Visual System


FIGURE 3.2 The ElectromagneticSpectrum Human eyes can perceive only a very thin band of electromagnetic waves, known as the visible spectrum.


Vision:Sensing Color

• Perception of Color – results from reflection of particular

wavelengths of the visual spectrum– three dimensions of light produce color

distinctions

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FIGURE 3.5 Hue, Brightness, and SaturationManipulations of hue, brightness, and saturation alter the appearance of a photo. (1) natural color; (2) altered hues; (3) altered brightness; (4) altered saturation.


VisionSensing Color: Dimensions of Light• Hue

– the specific color perceived• Saturation

– the purity of a color• Brightness

– the intensity of the light energy perceived as a color

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Vision - Sensing Color:Theories of Color Vision

• Trichromatic Theory– There are 3 types of cones in the retina.– Each is sensitive to 1 of 3 colors.

blue, green, or red

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• Opponent-Process Theory– Cells respond by increasing or

decreasing their rate of firing when different colors are present. red/green cells: increase rate with red,

decrease with green yellow/blue cells: increase with yellow,

decrease with blue white/black cells: increase rate with

white, decrease with black

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• Opponent-Process Theory– Afterimage

visual sensation that remains after the stimulus is withdrawn

The brain will give the sensation of the opposite color.

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• Which theory is correct?– Each theory explains a different phase

of color processing. Trichromatic theory best explains cone

processing of color. opponent-process theory: cones pass on

information about wavelengths to ganglion cells

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Vision:Colorblindness

• Inability to distinguish certain colors from one another

• Eight percent of males and one percent of females experience difficulty distinguishing colors.

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Vision:Colorblindness

• Distinguishing red from green is the most common form of color blindness.

• Color blindness can have degrees due to:– differences related to the number of

color vision genes individual has– genetic differences in the way that

types of cones are distributed in the retina

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Hearing and Balance:Sound

• Sound requires a medium, such as air or water, through which to move.

• Frequency– number of cycles completed by sound

wave in one second– determines the pitch of a sound– measured in hertz (Hz)

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Hearing and Balance:Sound

• Amplitude– loudness of sound– measured in decibels (dB)

• Timbre– quality of a sound that distinguishes it

from other sounds of the same pitch and loudness

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FIGURE 3.7 Decibel Levels of Various SoundsThe loudness of a sound (its amplitude) is measured in decibels. Each increase of 10 decibels makes a sound 10 times louder. A normal conversation at 3 feet measures about 60 decibels, which is 10,000 times louder than a soft whisper of 20 decibels. Any exposure to sounds of 130 decibels or higher puts a person at immediate risk for hearing damage, but levels as low as 90 decibels can cause hearing loss if one is exposed to them over long periods of time.


Hearing and BalanceSound: Decibels

• Amplitude is measured in decibels.• Each increase of 10 decibels makes a

sound 10 times louder.• Exposure to 130 decibels or higher

creates a risk for hearing damage.

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Sound:The Ear and Hearing

• Audition – sensation and process of hearing

• Outer Ear– pinnea and auditory canal

• Middle Ear– ossicles

hammer, anvil, and stirrup• Inner Ear

cochlea and semicircular canals

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FIGURE 3.8 The Anatomy of the HumanEar Sound waves pass through the auditory canal to the eardrum, causing it to vibrate and set in motion the ossicles in the middle ear. When the stirrup pushes against the oval window, it sets up vibrations in the inner ear. This moves the fluid in the cochlea back and forth and sets in motion the hair cells, causing a message to be sent to the brain via the auditory nerve.


Sound:How Sound Waves Are Converted• Sound waves enter the pinna, the

visible part of the outer ear.• Waves travel the auditory canal, which

causes the eardrum to vibrate. • Ossicles in the middle ear amplify

sound waves.• Amplified waves cause vibration of the

oval window.

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Sound:How Sound Waves Are Converted• The oval window initiates activity in

inner ear, sets cochlea fluid in motion.• Fluid pushes and pulls the hair cells

attached to the basilar membrane.• Basilar membrane transduces

vibrations into neural impulses.• The auditory nerve carries neural

impulses to the brain.

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Hearing and Balance:Sound-Hearing Theories

• Place Theory– Each pitch is determined by the location

along the basilar membrane of the cochlea that vibrates the most.

– This theory explains how we hear sounds with frequencies higher than 1000 Hz.

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Hearing and Balance:Sound-Hearing Theories

• Frequency Theory– Hair cell receptors vibrate the same

number of times per second as do the sounds that reach them.

– This theory explains how low-frequency sounds are heard.

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Balance and Movement:Kinesthetic Sense

• Provides information about:– The position of body parts in relation to

each other – Movement of the entire body or its parts

• Information detected by receptors in joints, ligaments, and muscles

• Other senses provide additional information about body position and movement.

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FIGURE 3.10 Sensing Balance andMovement You sense the rotation of your head in any direction because the movement sends fluid coursing through the tubelike semicircular canals in the inner ear. The moving fluid bends the hair cell receptors, which, in turn, send neural impulses to the brain.


Balance and Movement:Vestibular Sense

• Detects movement, information about body's orientation in space

• Located in semicircular canals and vestibular sacs of the inner ear

• Semicircular canals sense rotation of head.– canals filled with fluid– moving fluid moves hair cells– hair cells send input to brain

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FIGURE 3.11 The Olfactory SystemOdor molecules travel up the nostrils to the olfactory epithelium, which contains the receptor cells for smell. Olfactory receptors are special neurons whose axons form the olfactory nerve. The olfactory nerve relays smell messages to the olfactory bulbs, which pass them on to the amygdala and olfactory cortex. From there, they go to the limbic system, the thalamus, and orbitofrontal cortex.


Smell Taste and Touch:Smell

• Olfaction: sense of smell– aids in survival– influences emotional states– serves as a memory cue

Smell, Taste, and Touch:Smell

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FIGURE 3.11 The Olfactory SystemOdor molecules travel up the nostrils to the olfactory epithelium, which contains the receptor cells for smell. Olfactory receptors are special neurons whose axons form the olfactory nerve. The olfactory nerve relays smell messages to the olfactory bulbs, which pass them on to the amygdala and olfactory cortex. From there, they go to the limbic system, the thalamus, and orbitofrontal cortex.


Smell: How Smell Travels from the Nose to the Brain

• Olfactory Epithelium– one-inch square patches of tissue– one at the top of each nasal cavity– contain olfactory neurons

• Olfactory Bulbs– structures above the nasal cavity – where smell sensations first register in

the brain

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Smell: How Smell Travels from the Nose to the Brain

• Orbitofrontal Cortex– receives messages from olfactory bulbs

via the thalamus

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Smell Taste and Touch:Taste

• Gustation: sense of taste• Five primary taste sensations have

been identified.– Sweet– Sour– Salty– Bitter

Smell, Taste, and Touch:Smell

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Smell, Taste, and Touch:Taste

• Five primary taste sensations have been identified.– Umami

recent identification by researchers sensation is triggered by glutamate

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FIGURE 3.12 The Tongue’s Papillae and Taste Buds(a) A photomicrograph of the surface of the tongue shows several papillae. (b) This vertical cross-section through a papilla reveals the location of the taste buds and taste receptors.


Taste:How Sensations Are Detected

• Papillae– small bumps on the tongue

• Taste buds lie alongside some of the papillae.– Each taste bud is composed of 60 to

100 receptor cells.– All 5 taste sensations can be detected

on all locations of tongue.

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Taste:Nontasters and Supertasters

• Individuals vary widely in their capacity for experiencing taste sensations.

• Nontasters – unable to taste certain sweet and bitter

compounds• Supertasters

– taste sweet and bitter compounds with far stronger intensity than other people

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Taste:Nontasters and Supertasters

• Researchers are investigating links between taste sensitivity, eating behaviors, and health.

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Touch:Transmission of Touch Sensation

• Tactile (touch) information is conveyed to the brain when an object touches and depresses the skin.– One or more of several types of

receptors are stimulated.– Touch messages are sent through nerve

connections to the spinal cord.– The message is relayed next to the

somatosensory cortex of cerebrum.

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Touch:Transmission of Touch Sensation

• Two-Point Threshold– measure of how far apart 2 touch points

on the skin must be before they are felt as 2 separate touches

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Pain:The Gate Control Theory

• An area in the spinal cord acts as a gate and blocks or transmits pain messages to the brain.

• Pain messages are carried by small, slow-conducting nerve fibers.

• Large, fast-conducting nerve fibers carry other sensory messages.

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Pain:The Gate Control Theory

• Messages from fast-conducting fibers– "tie up" gate – prevent pain message from

transmission to the brain• Rub or apply gentle pressure to injury.

– Large, fast-conducting nerve fibers are stimulated.

– Pain message is blocked.

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Pain: Functions of Pain, Cross-cultural Variations, Role of Endorphins

• Pain can be a valuable warning and a protective mechanism.– Pain motivates people to tend to an

injury, to restrict activity, and to seek medical help.

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• Distraction can be effective with short-term pain, but not long-term pain.

• Cross-cultural variations in chronic pain may be linked to differences in people's emotional states.

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• Endorphins are natural painkillers produced by the body.– block pain and produce a feeling of well-

being– Some individuals release endorphins

when they think they are receiving pain medication.

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Influences on Perception

• Perception – process through which the brain assigns

meaning to sensations– influenced by 3 factors

Attention Prior knowledge Cross-modal perception

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Influences on Perception:Attention

• Process of sorting through sensations and selecting some for further processing

• When attention is focused on some sensations, others are missed altogether or misperceived.– inattentional blindness

Attention is shifted from one object to another.

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Influences on Perception:Attention

• When attention is focused on some sensations, others are missed altogether or misperceived.– inattentional blindness

fail to notice changes in objects not receiving direct attention

– cocktail party phenomenon Auditory attention focuses on information

that is personally meaningful.

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Principles of Perception:Information from Multiple Sources • Cross-Modal Perception

– the process by which the brain integrates information from more than one sense

– Cross-modal perception is used to process complex stimuli such as speech.

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Influences on Perception:Prior Knowledge

• Bottom-Up Processing– also called data-driven processing– This strategy involves looking for

patterns in individual bits of information that can be interpreted using prior knowledge.

• Top-Down Processing– also known as concept-driven

processing

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Influences on Perception:Prior Knowledge

• Top-Down Processing– Prior knowledge limits the range of

one's guesses by providing a "whole" that can serve as a context for individual bits of information.

• Perceptual Set– The expectation of what will be

perceived can affect that which is perceived.

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Influences on Perception:Social Perception

• Mirror Neuron System (MNS)– A network of cells that the brain uses to

interpret and produce motor actions and emotion-related behavior.

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FIGURE 3.14 Gestalt Principles of Perceptual OrganizationGestalt psychologists proposed several principles of perceptual organization, including figure–ground, similarity, proximity, continuity, and closure.


Principles of Perception: Gestalt Principles of Perceptual Organization• Sensory elements experience brought

together as a whole• Gestalt: a German word that refers to

the whole form, pattern, or configuration that a person perceives

• Sensory experience is organized according to basic principles of perceptual organization.

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Principles of Perception:Perceptual Constancy

• Perceptual Constancy – The phenomenon that allows us to

perceive objects as maintaining stable properties, such as size, shape, and brightness, despite differences in distance, viewing angle, and lighting.

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FIGURE 3.15 Shape ConstancyThe door projects very different images on the retina when viewed from different angles. But because of shape constancy, you continue to perceive the door as rectangular.


Principles of Perception:Depth Perception

• The ability to perceive the visual world in 3 dimensions and to judge distances accurately

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• How do eyes create dimensionality from a one-dimensional image on the retina?– depth cues

monocular – types include: interposition, linear

perspective, relative size, texture gradient, atmospheric perspective, shadow or shading, and motion parallax

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• How do eyes create dimensionality from a one-dimensional image on the retina?– depth cues

binocular– types include: convergence and binocular

(retinal) disparity

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• Both types of cues depend on both eyes working together– convergence

Eyes turn inward to focus on nearby objects—the closer the object, the more the objects appear to come together

– binocular (or retinal) disparity difference between retinal images

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FIGURE 3.16 Retinal Disparity and Viewing a StereogramRetinal disparity enables most of us to perceive 3-D images in stereograms. Place this picture against the tip of your nose and then very, very slowly move the book straight back from your face. Look at the image without blinking. A 3-D image will suddenly appear.


FIGURE 3.17 Monocular Depth Cues


Depth Perception:Monocular Depth Cues

• Perceived by one eye alone• Seven cues• Many have been used by artists to give

the illusion of depth to their paintings.

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Depth Perception:Monocular Depth Cues

• Interposition• Linear perspective• Relative size• Texture gradient• Atmospheric perspective• Shadow or shading• Motion parallax

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Principles of Perception:Perception of Motion

• Brain perceives real motion by comparing the movement of images across the retina to visual reference points.

assumes points to be stable

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• Autokinetic Illusion– An unmoving light in a dark room

appears to move. In reality, the eyes are moving: not the

light. In the dark, the brain has no stable

reference point to determine what is moving.

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• Phi Phenomenon (Stroboscopic Motion)– The sequential flashing of stationary

lights gives the perception of the light as moving.

– Movies are an example of phi phenomena.

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Unusual Perceptual Experiences

• Sensation and perception enable us to make sense of the world.

• What happens when these vital processes lead us to believe that we sense something that really isn't there?

• Is it possible to perceive without sensing?

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FIGURE 3.18 Some Puzzling Perceptions(a) Do you see random dots or something else? (b) Why couldn’t you build a replica of this three-pronged device? (c) Which horizontal line appears to be longer? (d) Which monster is larger?


Unusual Perceptual Experiences:Puzzling Perceptions

• Ambiguous Figures– The perceptual system tries to resolve

the uncertainty by seeing the figure first one way and then another (figures [a] and [b]).

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FIGURE 3.18 Some Puzzling Perceptions(a) Do you see random dots or something else? (b) Why couldn’t you build a replica of this three-pronged device? (c) Which horizontal line appears to be longer? (d) Which monster is larger?


Unusual Perceptual Experiences:Puzzling Perceptions

• Illusions– false perceptions or misperceptions of

an actual stimulus in the environment Figure (c) shows the Müller-Lyer illusion. Figure (d) shows the Ponzo illusion.

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Unusual Perceptual Experiences: Subliminal Perception ESP and Synesthesia

• Subliminal Perception – capacity to perceive and respond to

stimuli below the level of awareness– appears ineffective at persuading

people to buy products

Unusual Perceptual Experiences: Subliminal Perception, ESP, and Synesthesia

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• ESP– gaining information through channels

other than known sensory ones– Researchers have been unable to

replicate experiments that support its existence.

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• Synesthesia – Humans may be born with the capacity.– lose it as brain becomes more

specialized during childhood

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