Sensation & PerceptionSensation & Perception

To represent the world, we must detect To represent the world, we must detect physical energy (a stimulus) from the physical energy (a stimulus) from the

environment and convert it into neural environment and convert it into neural signals. This is a process called signals. This is a process called sensation..

When we select, organize, and interpret our When we select, organize, and interpret our sensations, the process is called sensations, the process is called

perception..

Sensation provides the raw information that Sensation provides the raw information that perception constructs into our experiences.perception constructs into our experiences.

“The Forest Has Eyes,” Bev Doolittle

Absolute ThresholdAbsolute ThresholdWeakest amount of a stimulus that can be Weakest amount of a stimulus that can be sensedsensed

We only sense things we can perceiveWe only sense things we can perceive

Vision: A candle flame viewed from 30 miles Vision: A candle flame viewed from 30 miles on a dark nighton a dark night

Hearing: Ticking watch from 20 feet in Hearing: Ticking watch from 20 feet in quiet roomquiet room

Sensory AdaptationSensory Adaptation

Diminished sensitivity as a consequence of Diminished sensitivity as a consequence of constant stimulation.constant stimulation.

Put a band aid on your arm and after awhileyou don’t sense it.

VisionVision

LightLight

““Visual Capture” Vision dominates our other sensesVisual Capture” Vision dominates our other senses

Light is electromagnetic energyLight is electromagnetic energy

Described in wavelengthsDescribed in wavelengths

VisibleSpectrum

The Stimulus Input: Light The Stimulus Input: Light EnergyEnergy

• Humans detect visible light.

• Bee’s detect radiation from UV into violet/blue end of the visible spectrum.

• The energy of red light does NOT stimulate bees receptors – so transduction does NOT occur.

Physical Characteristics of Physical Characteristics of LightLight

Light travels as an electromagnetic Light travels as an electromagnetic wavewave..

Sounds travels as a Sounds travels as a wavewave of air pressure. of air pressure.

Physical Physical CharacteristicCharacteristic

ssLightLight SoundSound

WavelengthWavelength ColorColor PitchPitch

AmplitudeAmplitude

(Intensity)(Intensity)WavelengtWavelengt

hhVolumeVolume

The EyeThe Eye

Parts of the eyeParts of the eye

1.1. Iris:Iris: Muscle that expands and contracts Muscle that expands and contracts to change the size of the opening (pupil) to change the size of the opening (pupil) for light.for light.

2.2. Lens:Lens: changing thickness projects an changing thickness projects an image onto the retinaimage onto the retina

3.3. Retina:Retina: Contains sensory receptors that Contains sensory receptors that process visual information and sends it process visual information and sends it to the brain (includes photoreceptors)to the brain (includes photoreceptors)

PhotoreceptorsPhotoreceptors

E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Visual Information ProcessingVisual Information Processing

Optic nerves connect to the thalamus in the Optic nerves connect to the thalamus in the middle of the brain, and the thalamus middle of the brain, and the thalamus

connects to the visual cortex.connects to the visual cortex.

Visual AcuityVisual AcuityThe ability to see visual detailsThe ability to see visual details

Nearsighted: need to be close to an object to see itNearsighted: need to be close to an object to see itFarsighted: need to be further from an object to Farsighted: need to be further from an object to

see itsee it

Blue Green Red

Medium LowMax

Opponent-Process TheoryOpponent-Process TheoryOpposing retinal processes enable color vision.Opposing retinal processes enable color vision.

Red-GreenRed-Green

Yellow-BlueYellow-Blue

White-BlackWhite-Black

Cells stimulated by green are inhibited by red.Cells stimulated by green are inhibited by red.

AfterimagesAfterimages::

We tire our green response by staring at green.We tire our green response by staring at green.

We then stare at white (all colors)We then stare at white (all colors)

Only red will fire normally.Only red will fire normally.

Color BlindnessColor Blindness

Ishihara Test

Genetic disorder in which people are blind Genetic disorder in which people are blind to green or red colors. Partially or totally to green or red colors. Partially or totally

unable to see colorsunable to see colors

Partial Color blindness common (esp Partial Color blindness common (esp red-green 99%)red-green 99%)

Inherited + more male than female (8% vs Inherited + more male than female (8% vs 1%)1%)

No cures, mostly an annoyance (unless No cures, mostly an annoyance (unless driving!)driving!)

HearingHearing

SoundSound

Sound waves are vibrations Sound waves are vibrations

Pitch: high or low a sound is. Depends Pitch: high or low a sound is. Depends on the frequency of sound waveson the frequency of sound waves

Loudness: determined by the height of Loudness: determined by the height of sound waves. Measured in decibals sound waves. Measured in decibals

Sound CharacteristicsSound Characteristics

1.1. Frequency or Wavelength Frequency or Wavelength (pitch)(pitch)

2.2. Amplitude or Intensity Amplitude or Intensity (loudness)(loudness)

Intensity (Loudness)Intensity (Loudness)

Intensity Intensity (Loudness):(Loudness):

Amount of energy Amount of energy in a wave, in a wave,

determined by the determined by the amplitude, relates amplitude, relates to the perceived to the perceived

loudness.loudness.

Frequency (Pitch)Frequency (Pitch)

Frequency Frequency (pitch):(pitch): TheThe dimension of dimension of

frequency frequency determined by determined by

the wavelength of the wavelength of sound.sound.

Wavelength:Wavelength: The The distance from the distance from the peak of one wave peak of one wave to the peak of the to the peak of the

next.next.

Loudness of SoundLoudness of Sound

70dB

120dB

Richard K

aylin/ Stone/ Getty Im

ages

Deaf CultureDeaf Culture

Cochlear implants are electronic devices Cochlear implants are electronic devices that enable the brain to hear soundsthat enable the brain to hear sounds

Deaf Musician

Sometimes, deafness is a difference NOT disability

More acceptance in society, ASL, closed captioning, interpreters

DeafnessDeafnessCauses: Inherited, disease, injury, old ageCauses: Inherited, disease, injury, old age

Conductive Deafness: damage to the middle ear. Struggles with amplifying soundConductive Deafness: damage to the middle ear. Struggles with amplifying sound

Sensorineural Deafness: damage to inner ear. Cannot perceive certain frequenciesSensorineural Deafness: damage to inner ear. Cannot perceive certain frequencies

Other SensesOther Senses

TouchTouch

The sense of touch is a mix of four distinct skin The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain.senses—pressure, warmth, cold, and pain.

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PainPain

Pain tells the body that something has gone Pain tells the body that something has gone wrong. Usually pain results from damage to the wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in skin and other tissues. A rare disease exists in

which the afflicted person feels no pain.which the afflicted person feels no pain.

Ashley Blocker (right) feels neither painnor extreme hot or cold.

AP Photo/ Stephen M

orton

Biopsychosocial InfluencesBiopsychosocial Influences

Pain ControlPain Control

Pain can be controlled by a number of Pain can be controlled by a number of therapies including, drugs, surgery, therapies including, drugs, surgery,

acupuncture, exercise, hypnosis, and even acupuncture, exercise, hypnosis, and even thought distraction.thought distraction.

Todd R

ichards and Aric V

ills, U.W

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Hunter H

offman, w

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.vrpain.com

TasteTaste

Traditionally, taste sensations consisted of Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. sweet, salty, sour, and bitter tastes.

Recently, receptors for a fifth taste have Recently, receptors for a fifth taste have been discovered called been discovered called “Umami”.“Umami”.

Sweet Sour Salty Bitter Umami(Fresh

Chicken)

Sensory InteractionSensory Interaction

When one sense affects another sense, When one sense affects another sense, sensory interactionsensory interaction takes place. So, the takes place. So, the taste of strawberry interacts with its smell taste of strawberry interacts with its smell and its texture on the tongue to produce and its texture on the tongue to produce

flavor.flavor.

SmellSmellLike taste, smell is a chemical sense. Like taste, smell is a chemical sense.

Odorants enter the nasal cavity to stimulate Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. Unlike 5 million receptors to sense smell. Unlike taste, there are many different forms of taste, there are many different forms of

smell.smell.

Smell and MemoriesSmell and Memories

The brain region for The brain region for smell (in red) is smell (in red) is

closely connected closely connected with the brain with the brain

regions involved regions involved with memory (limbic with memory (limbic system). That is why system). That is why strong memories are strong memories are

made through the made through the sense of smell.sense of smell.

Body Position and MovementBody Position and Movement

The sense of our body parts’ position and The sense of our body parts’ position and movement is called movement is called kinesthesiskinesthesis. The . The

vestibular sensevestibular sense monitors the head (and monitors the head (and body’s) position. body’s) position.

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Perceptual OrganizationPerceptual Organization

When vision competes with our others senses, our When vision competes with our others senses, our vision usually wins – a phenomenon called vision usually wins – a phenomenon called visual visual

capturecapture..

How do we form meaningful perceptions from How do we form meaningful perceptions from sensory information?sensory information?

We organize it. We organize it. GestaltGestalt psychologists showed that psychologists showed that the brain creates a coherent perceptual experience the brain creates a coherent perceptual experience

that is more than simply a sum of the available that is more than simply a sum of the available sensory information, and it does this in predictable sensory information, and it does this in predictable

ways. ways. Gestalt psychologyGestalt psychology examines a person’s examines a person’s total experience because the way we experience the total experience because the way we experience the world is more than just an accumulation of various world is more than just an accumulation of various

perceptual experiences. perceptual experiences.

Organization of the visual field into objects Organization of the visual field into objects (figures) that stand out from their (figures) that stand out from their

surroundings (ground).surroundings (ground).

Form PerceptionForm Perception

Tim

e Savings S

uggestion, © 2003 R

oger Sheperd.

GroupingGroupingAfter distinguishing the figure from the After distinguishing the figure from the

ground, our perception needs to organize ground, our perception needs to organize the figure into a meaningful form using the figure into a meaningful form using

grouping rules.grouping rules.

Closure - Objects that make up a recognizable image, despite possibly containing gaps that the mind needs to fill in.

Grouping & RealityGrouping & Reality

Although grouping principles usually help us Although grouping principles usually help us construct reality, they may occasionally lead us construct reality, they may occasionally lead us

astray.astray.

Both photos by W

alter Wick. R

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Depth PerceptionDepth Perception

Visual Cliff

Depth perception enables us to judge distances. Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. infants (crawling age) have depth perception. Even newborn animals show depth perception.Even newborn animals show depth perception.

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Binocular CuesBinocular CuesRetinal disparity (or binocular disparity):Retinal disparity (or binocular disparity): Images Images from the two eyes differ. Try looking at your two index from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in the eyes. You will see a “finger sausage” as shown in the

inset. inset.

Monocular CuesMonocular Cues

Relative Size:Relative Size: If two objects are similar in If two objects are similar in size, we perceive the one that casts a size, we perceive the one that casts a

smaller retinal image to be farther away.smaller retinal image to be farther away.

Monocular CuesMonocular Cues

Interposition:Interposition: Objects that occlude (block) Objects that occlude (block) other objects tend to be perceived as other objects tend to be perceived as

closer.closer.R

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Monocular CuesMonocular Cues

Relative Height:Relative Height: We perceive objects that are higher in We perceive objects that are higher in our field of vision to be farther away than those that are our field of vision to be farther away than those that are

lower.lower.

Image courtesy of S

haun P. V

ecera, Ph. D

., adapted from

stimuli that appered in V

ecrera et al., 2002

Monocular CuesMonocular CuesRelative motion:Relative motion: Objects closer to a fixation Objects closer to a fixation point move faster and in opposing direction to point move faster and in opposing direction to

those objects that are farther away from a fixation those objects that are farther away from a fixation point, moving slower and in the same direction. point, moving slower and in the same direction.

Monocular CuesMonocular CuesLinear Perspective:Linear Perspective: Parallel lines, such as Parallel lines, such as railroad tracks, appear to converge in the railroad tracks, appear to converge in the distance. The more the lines converge, the distance. The more the lines converge, the

greater their perceived distance.greater their perceived distance.

Monocular CuesMonocular CuesLight and Shadow:Light and Shadow: Nearby objects reflect more Nearby objects reflect more

light into our eyes than more distant objects. light into our eyes than more distant objects. Shading can imply where a light source is and thus Shading can imply where a light source is and thus imply depth and position. The ones that are shaded imply depth and position. The ones that are shaded

on the left seem to be sticking out towards us. on the left seem to be sticking out towards us.

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cientific Am

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ll rights reserved.

Perceptual ConstancyPerceptual Constancy

Perceiving objects as unchanging Perceiving objects as unchanging even as illumination and retinal even as illumination and retinal

images change. images change.

Perceiving familiar objects as having consistent Perceiving familiar objects as having consistent color even when changing illumination filters color even when changing illumination filters

the light reflected by the object.the light reflected by the object.

Color ConstancyColor Constancy

Color Constancy

Size-Distance RelationshipSize-Distance Relationship

The distant monster (below, left) and the The distant monster (below, left) and the top red bar (below, right) appear bigger top red bar (below, right) appear bigger

because of distance cues.because of distance cues.

From Shepard, 1990

Size-Distance RelationshipSize-Distance Relationship

Both girls in the room are of similar Both girls in the room are of similar height. However, we perceive them to be height. However, we perceive them to be of different heights as they stand in the of different heights as they stand in the

two corners of the room.two corners of the room.

Both photos from S. Schwartzenberg/ The Exploratorium

Ames RoomAmes Room

The Ames room is designed to demonstrate the size-distance illusion.

Lightness ConstancyLightness Constancy

The color and brightness of square A and B are the same.

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Perceptual InterpretationPerceptual Interpretation

Immanuel Kant (1724-1804) maintained that Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of knowledge comes from our inborn ways of

organizing sensory experiences.organizing sensory experiences.

John Locke (1632-1704) argued that we learn John Locke (1632-1704) argued that we learn to perceive the world through our to perceive the world through our

experiences.experiences.

How important is experience in shaping ourperceptual interpretation?

Sensory Deprivation & Restored Vision

After cataract surgery, blind adults were able to regain sight. These

individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle

and a triangle (Von Senden, 1932).

Facial RecognitionFacial Recognition

After blind adults After blind adults regained sight, they regained sight, they

were able to recognize were able to recognize distinct features, but distinct features, but

were unable to were unable to recognize faces. recognize faces.

Normal observers also Normal observers also show difficulty in facial show difficulty in facial recognition when the recognition when the

lower half of the lower half of the pictures are changed.pictures are changed.

Courtesy of R

ichard LeG

rand

Kittens raised Kittens raised without exposure without exposure to horizontal lines to horizontal lines later had difficulty later had difficulty

perceiving perceiving horizontal bars.horizontal bars.

Blakemore & Cooper (1970)

Sensory DeprivationSensory Deprivation

Perceptual AdaptationPerceptual Adaptation

Visual ability to Visual ability to adjust to an adjust to an

artificially displaced artificially displaced visual field, e.g., visual field, e.g., prism glasses.prism glasses.

Courtesy of H

ubert Dolezal

Perceptual SetPerceptual Set

A mental predisposition to perceive one thing A mental predisposition to perceive one thing and not another. What you see in the center and not another. What you see in the center picture is influenced by flanking pictures.picture is influenced by flanking pictures.

From

Shepard, 1990.

(a) Loch ness monster or a tree trunk; (b) Flying

saucers or clouds?

Perceptual SetPerceptual Set

Other examples of perceptual set.Other examples of perceptual set.

Frank Searle, photo Adam

s/ Corbis-Sygm

a

Dick R

uhl

To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting

under a tree.

Cultural ContextCultural ContextContext instilled by culture also alters Context instilled by culture also alters

perception. perception.

Perception RevisitedPerception Revisited

Is perception innate or acquired? Is perception innate or acquired?

Is There Extrasensory Is There Extrasensory Perception?Perception?

Perception without sensory input is called Perception without sensory input is called extrasensory perception (ESP). A large extrasensory perception (ESP). A large

percentage of scientists do not believe in percentage of scientists do not believe in ESP.ESP.

Claims of ESPClaims of ESP

1.1. Telepathy:Telepathy: Mind-to-mind communication. Mind-to-mind communication. One person sending thoughts and the One person sending thoughts and the other receiving them. other receiving them.

2.2. Clairvoyance:Clairvoyance: Perception of remote Perception of remote events, such as sensing a friend’s house events, such as sensing a friend’s house on fire.on fire.

3.3. Precognition:Precognition: Perceiving future events, Perceiving future events, such as a political leader’s death.such as a political leader’s death.