Sensation & PerceptionUnit #3, Entry #1

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Sensation & Perception

How do we construct our representations of the external world?

Sensation: stimulation of sensory receptors (eyes, ears, tongue, etc.) and the transmission of sensory information to the brain5 senses: sight, sound, touch, taste, smellPerception: the psychological process through which your brain interprets sensory info

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Sensing the World

Senses are nature’s gift that suit an organism’s needs.

A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

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Exploring the Senses

1. What stimuli cross our threshold for conscious awareness?

2. Could we be influenced by stimuli too weak (subliminal) to be perceived?

3. Why are we unaware of unchanging stimuli, like a band-aid on our skin?

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Psychophysics

A study of the relationship between physical characteristics of stimuli and

our psychological experience with them.

Physical World

Psychological World

Light Brightness

Sound Volume

Pressure

Weight

Sugar Sweet

-What stimuli can we detect?-At what intensity?-How sensitive are we to changing stimuli?

Several Concepts influence our sensation and perception:

1.) Absolute Threshold: the weakest/smallest amount of a stimulus that can be sensed.

ex: can you taste a single drop of lemon juice in a bottle of water?

Ex2 :

*Is different for everyone.

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No

Detection

Intensity

AbsoluteThreshold

Detected

YesYesNo No

Observer’s Response

Tell when you (the observer) detect the light.

Several Concepts influence our sensation and perception:

• 2.) Difference Threshold: The smallest amount of a difference that can be detected between two stimuli– Ex: can you tell the

difference between 2 orange paint chips that are only a shade different in color?

– Ex 2:

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Difference Threshold

Difference Threshold: also called just noticeable difference (JND).

DifferenceThreshold

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

No

Observer’s Response

No Yes

Several Concepts influence our sensation and perception:

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

• Ex:

Several concepts influence our sensation and perception:

• 4.) Signal Detection Theory: belief that we distinguish and focus on different sensory stimuli based on their strengths, the setting we are in, our physical state, mood, and attitude.– Ex: do you notice when someone walks into the

room? When a teacher calls your name?– Ex 2:*We focus on what we consider important!

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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).

Detection depends on:

Person’s experienceExpectationsMotivationLevel of fatigue

Carol L

ee/ Tony Stone Images

Several concepts influence our sensation and perception:

• 5.) Sensory Adaptation: Process by which we adapt to the sensory stimuli in our environment.– Ex: walk into dark theater, can’t see at first. Eyes

adjust, then you can see– Ex 2:

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

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Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

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

Subliminal Threshold

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Subliminal Threshold: When stimuli are below one’s absolute threshold

for conscious awareness.

Kurt Scholz/ Superstock

Subliminal Threshold

• Can we unconsciously sense subliminal stimuli?

• Without our conscious awareness of the stimuli, can they have suggestive powers and influence our thoughts and/or behaviors?

Subliminal Threshold

Can we unconsciously sense subliminal stimuli?

– The answer to a certain extent seems to be yes!• Sometimes we feel what we do not know and cannot

describe = intuition• Subliminal stimuli may evoke a feeling, though not a

conscious awareness of the stimulus*MUCH OF OUR INFORMATION PROCESSING OCCURS AUTOMATICALLY, OUT OF SIGHT, OFF THE RADAR SCREEN OF OUR CONSCIOUS MIND!

Subliminal Threshold

• Without our conscious awareness of the stimuli, can they have suggestive powers and influence our thoughts and/or behaviors?– Subliminal messaging in advertising, music, self-help

tapes, etc.– Yes, it is possible for them to have a subtle, fleeting effect.– But there is no evidence of a strong or lasting influence

on one’s behavior. • Self-help tape study 1991• We are vulnerable to placebo effect- our expectations or what

we are told should happen.

http://wtso.net/movie/346-1214%20%20New%20Kids%20on%20the%20Blecch.html

Subliminal Threshold

• Priming:– The activation, often unconsciously, of certain

associations, thus predisposing a person’s memory, perception, or reponse.

– http://www.thepsychfiles.com/gestalt/

– *those who saw pictures of animals were influenced to see the horse

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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: Transparent

structure behind the pupil that changes

shape to focus images on the retina.

Accommodation: The process by which the eye’s lens changes shape to help focus

near or far objects on the retina.

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The Lens

Nearsightedness: A condition in which nearby objects are seen more clearly

than distant objects.

Farsightedness: A condition in which faraway objects are seen more clearly than near objects.

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Retina

Retina: The light-sensitive inner surface of the

eye, containing receptor rods and cones in

addition to layers of other neurons (bipolar, ganglion

cells) that process visual information.

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Optic Nerve, Blind Spot & Fovea

http://www.bergen.org

Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster.

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Photoreceptors

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

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Bipolar & Ganglion Cells

Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which are for the optic

nerve.

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Visual Information Processing

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

connects to the visual cortex.

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

eau Lotto at U

niversity College, L

ondon

Pages 85-88

• http://www.clipsforclass.com/sandp• Science of Sound clip

How do you hear?

• Sound travels through the air in waves and creates vibrations

(Ever felt your clothes vibrating from loud music?)

– Each vibration is called a cycle or wavelength

• Pitch: how high or low a sound is– Shorter wavelengths vibrate more frequently

= create a higher pitch– Longer wavelengths vibrate fewer times

= create a lower pitch

Pitch

• The greater the number of cycles per second, the higher the pitch.

Loudness• Amplitude – height• The higher the

amplitude of a wave, the louder the sound.

• Decibel – A unit expressing the loudness of a sound. Abbreviated dB.

Loudness of Sound

70dB

120dB

Richard K

aylin/ Stone/ Getty Im

ages

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Localization of Sounds

Because we have two ears, sounds that reach one ear faster than the other ear

cause us to localize the sound.

Hearing Loss

Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

Sensorineural Hearing Loss: Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness.

• http://www.clipsforclass.com/sandp• Tinnutus clip

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Other Important Senses

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

pain.

Bru

ce A

yers

/ Sto

ne/ G

etty

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ages

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Skin Senses

Only pressure has identifiable receptors. All other skin sensations are variations of

pressure, warmth, cold and pain.

Burning hot

Pressure Vibration Vibration

Cold, warmth and pain

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Pain

Pain tells the body that something has gone wrong. Usually pain

results from damage to the skin and other

tissues. A rare disease exists in which the

afflicted person feels no pain.

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

How we experience pain depends on: -our experiences and attention -our physiology -our cultural surroundings

=Biopsychosocial explanation

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Biopsychosocial Influences

What Causes Pain?

• Unlike vision, the pain system is not located in a simple nueral cord running from a sensing device to a definable brain area. And there is no one type of stimulus that triggers pain (as light triggers vision) and there are no special pain receptors (like rods and cones for vision)

What Causes Pain?

• Gate Control Theory:– The spine contains a neurological “gate” that

either blocks pain signals from being sent to the brain, or allows them to pass to the brain.

• Gate is opened by activity of pain signals• Gate can be closed by stronger activity messages from

other areas of the body (rubbing near the area of pain, accupuncture)

or by information from the brain (being distracted from something in environment, presence of endorphines

Gate-Control Theory

• One way to treat chronic pain is to stimulate it through massage by electrical stimulation or acupuncture. Rubbing causes competitive stimulation to pain thus reduces its effect.

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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 Richards and A

ric Vills, U

.W.

©H

unter Hoffm

an, ww

w.vrpain.com

Pain Control

• Burn victims can be distracted by allowing them to engage in illusory virtual reality. Their brain scans show differences in pain perceptions.

• Lamaze method of childbirth combines relaxation (through deep breathing and muscle relaxation), counterstimulation (through gentle message), and distraction (through focusing attention on a pleasant object or picture)