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Sensation

Chapter 5

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Sensation & Perception

Sensation: detecting physical energy (a stimulus) from the environment & converting it into neural signals.

Perception: selection, organization, and interpretation of sensations

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Top-Down ProcessingInformation processing(perception):

brain/mind => experience and expectations => interpretation

THE CHT

Analysis of the stimulus: sense receptors => brain/mind =>

interpretation

Bottom-up Processing

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Working Together: Bottom-Up & Top-Down

“The Forest Has Eyes,” Bev Doolittle

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Psychophysics

A study of the relationship between physical characteristics of stimuli and

our psychological experience with them.

Physical WorldPsychological

World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet

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No

Detection

Intensity

AbsoluteThreshold

Detected

YesYesNo No

Observer’s Response

Tell when you (the observer) detect the light.

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Thresholds

Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.

Pro

port

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of

“Yes”

Resp

on

ses

0.0

0

0

.50

1.0

0

0 5 10 15 20 25 Stimulus Intensity (lumens)

Some Threshold Tests:

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-Vision: candle flame on clear, dark night from 30 miles

-Hearing: ticking watch in a perfectly quiet room from 20 ft. -Taste: teaspoon of sugar diluted in 2 gallons of water

-Smell: drop of perfume diffused through a three room apartment

-Touch: the wing of a bee falling on your cheek from a ht. of 1 cm.

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Subliminal Threshold

Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness.

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“ALL GOOD TEENAGERS, TAKE OFF YOUR

CLOTHES”

Subliminal Sensation vs. Subliminal Persuasion

• Priming can influence feelings

• Self-help tapes, subliminal ads = no long-term influence on behavior

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Difference Threshold

Difference Threshold: Minimum difference between two stimuli required for

detection 50% of the time, also called just noticeable difference (JND).

DifferenceThreshold

Tell when you (observer) detect a difference in the light.

No

Observer’s Response

No Yes

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Weber’s Law

Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as

different.

StimulusConstant

(k)

Light 8%

Weight 2%

Tone 3%

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Signal Detection Theory (SDT)

Predicts how and when we detect the presence of a faint stimulus (signal) amid

background noise (other stimulation). SDT assumes that there is no single

absolute threshold and detection depends on:

Person’s experienceExpectationsMotivationLevel of fatigue

Carol L

ee/ Tony Stone Im

ages

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SDT Matrix

Decision

Yes No

Signal

Present Hit Miss

AbsentFalseAlarm

Correct Rejection

The observer decides whether she hears the tone or not, based on the signal being

present or not. This translates into four outcomes.

NOTE: Signal detection is different for everyone

Ex: Soldiers constantly on guard = notice more subtle signals (& false alarms)

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Sensory Adaptation

Constant stimulation = diminished sensitivity

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

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Now you see, now you don’tEven vision can suffer from desensitization.

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Vision

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Transduction

Sensory Transduction: transformation of stimulus energy into neural impulses.

Phototransduction: Conversion of light energy into neural impulses that the brain

can understand.

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Hue (color): determined by the

wavelength (peak to peak) of the light.

The Stimulus Input: Light Energy

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Wavelength (Hue)

Different wavelengths of light resultin different colors.

400 nm 700 nmLong wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

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Intensity (Brightness)

Intensity (brightness) Amount of energy in a

wave determined

by the amplitude.

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The Eye

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Parts of the eye

1. Cornea: Transparent tissue where light enters the eye.

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

3. Lens: Focuses the light rays on the retina.

4. Retina: Contains sensory receptors that process visual information and sends it to the brain.

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The LensLens changes shape to focus images on

the retina.

Accommodation: lens changing shape to

help focus near or far objects on the retina.Misshapen eyeball:

nearsitedness or farsightedness

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Retina

Retina: The light-sensitive inner surface of the eyeContains:-Receptor cells: Rods: b&w; night vision Cones: color; detail

-other neurons: (bipolar, ganglion cells) that process visual information.

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Test your Blind Spot

Close your left eye, and fixate your right eye on the black dot. Move the page

towards your eye and away from your eye. At some point the car on the right will

disappear due to a blind spot: point where the optic nerve leaves the eye where no

receptor cells are located

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Feature & Shape DetectionFeature: Nerve cells in the visual cortex respond to specific features, such as edges, angles, and

movement.

Shape: temporal lobe activity occurs as people

look at shoes, faces, chairs and houses.What do you see?

What does your brain see?

Brain uses feature & shape detection together to perceive patterns

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Visual Information ProcessingParallel Processing: brain processes several aspects

of the stimulus simultaneously.

Ex: brain divides a visual scene; processing allows us to perceive it as a integrated image

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Theories of Color VisionTrichromatic theory: (Helmholtz) normal retina contains three receptors that are sensitive to red, blue and green colors.- Colorblindness (red-green) supports this theory

Ishihara Test

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Staring at the green “deadens” the green neurons; thus the red fire

Theories of Color VisionOpponent-Process theory: (Hering) we process four primary colors combined in pairs of red-green, blue-yellow, and black-white.

• Color processing occurs in two stages:

1) Response to stimuli (Trichromatic)

2) Signals are processed/transmitted to visual cortex (Opponent-Process)

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Theories of Color Vision

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Color Constancy

Color of an object remains the same under different illuminations. However, when context

changes the color of an object may look different.

R. B

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niversity College, L

ondon

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Audition

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The Stimulus Input: Sound Waves

Acoustical transduction: Conversion of sound waves into neural impulses- sound influenced by amplitude, frequency, wavelength

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Loudness of Sound

70dB

120dB

Richard K

aylin/ Stone/ Getty Im

ages

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The Ear

Dr. Fred H

ossler/ Visuals U

nlimited

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The Hearing ProcessCochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

1) Outer ear funnels sound waves to the eardrum

2) Bones of mid. ear relay vibrations through oval window into fluid-filled cochlea

3) Pressure changes in cochlear fluid bends hair cells

4) Hair cell movements trigger nerve cells => auditory nerve

5) Auditory nerve => thalamus => auditory cortex

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Theories of AuditionPlace Theory: sound frequencies stimulate the basilar membrane at specific places resulting in perceived pitch. (best explains sensing high pitches)

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Theories of AuditionFrequency Theory: rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. (best explains sensing low pitches)

SoundFrequency

Auditory NerveAction Potentials

100 Hz200 Hz

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Localization of Sounds

Sounds that reach one ear faster than the other ear cause us to localize the sound.

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Hearing LossConduction Hearing Loss: damage to the mechanical system that conducts sound waves to the cochlea.Sensorineural Hearing Loss: caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness. (more common)Cochlear implants are electronic devices that enable the brain to hear sounds.

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Hearing DeficitsCan you hear that cell phone?

Older people tend to hear low frequencies well but suffer hearing loss when listening for high

frequencies.

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Other Important Senses

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

pain.

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Pain• Biopsychosocial Influences

• Gate-Control Theory (Melzak and Wall (1965, 1983))

– spinal cord contains neurological “gates” that either block pain or allow it to be sensed.

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Pain Control

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

acupuncture, exercise, hypnosis, and even thought distraction.

Todd R

ichards and Aric V

ills, U.W

. ©

Hunter H

offman, w

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.vrpain.com

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TasteTraditionally, taste sensations consisted of

sweet, salty, sour, and bitter tastes. Recently, receptors for a fifth taste have

been discovered called “Umami”.

Sweet

Sour

SaltyBitter

Umami(Fresh

Chicken)

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Smell Odorants enter the nasal cavity to stimulate 5 million receptors in the

Olfactory Bulb to sense smell.

Age, Gender, and SmellAbility to identify smell peaks during early adulthood, but steadily declines after that. Women are better at detecting odors than

men.

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Smell and Memories

The brain region for smell (in red) is

closely connected with the brain

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

made through the sense of smell.

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Body Position and Movement

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

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

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Whirling Dervishes Wire Walk

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Sensory Interaction

When one sense affects another sense, sensory interaction takes place. So, the

taste of strawberry interacts with its smell and its texture on the tongue to produce

flavor.

Synaesthesia – rare condition where one sensation produces another (ex: hearing a

sound produces a vision of a color)