Sensation

Psychophysics Thresholds (include JND) Attention and

discrimination Inattentional blindness Change blindness Pop-out phenomenon Stroop Effect

Sensation & Perception

How do we construct our representations of the external world?

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

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

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

Psychophysics

• Studies the links between physical stimuli in the world and the psychological experience of those stimuli

• Fechner, Wundt, Titchener, Weber• Among the earliest research to be

conducted in the field of Psychology

Bottom-up Processing (sensation)

Analysis of the stimulus begins with the sense receptors and works up to the level of

the brain and mind.

Letter “A” is sensed as a black blotch decomposed into features by the brain and

perceived as an “A” by our mind .

Top-Down Processing (perception)

Information processing guided by higher-level mental processes as we construct perceptions drawing on our experience

and expectations.

THE CHT

Our sensory and perceptual processes work together to help us sort out complex

images.

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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 or the feeling from our shoes?

Thresholds

Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50%

of the time.

For example, young children generally have a lower absolute threshold for sounds since the ability to detect sounds at the lowest

and highest ranges tends to decrease with age.

Subliminal Threshold

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

Detect it less than 50% of the time

Difference Threshold

Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable

difference (JND).

For example, if you were asked to hold two objects of different weights, the just noticeable difference would be the

minimum weight difference between the two that you could sense half of the time.

Weber’s Law explains the JND

Two stimuli must differ by a constant minimum proportion (rather than a

constant amount), to be perceived as different. Weber fraction: k = dI/I.

Stimulus Constant (k)

Light 8%

Weight 2%

Tone 3%

Signal Detection Theory

• Predicts when we will detect weak signals

• Ask why people respond differently to the same stimuli??

• Why does the same person’s response vary as the circumstance changes

• Sensitivity and responsiveness increases with emotional state

• Example: Hearing your baby cry…

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation. Sometimes referred to

as habituation

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

Selective AttentionPerceptions about objects change from moment to moment. Different forms of Necker cube become available to our

perception, however, one can pay attention only to one aspect of the object.

Necker Cube

Selective Attention

• Discrimination– we have the ability to filter out stimuli

rather than process every single stimuli that is bombarding our sensory receptors, will be helpful in conditioning (learning by association)

• Cocktail party effect– the ability to focus one's listening

attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

Inattentional Blindness

Inattentional blindness refers to inability to see a an object or a person amidst an

engrossing scene.

Keep your eye on the ball and count how many times the team with the white shirts

passes it…

Change Blindness

Change blindness is a form of inattentional blindness, where two-thirds of direction

giving individuals failed to notice a change in the individual who was asking for

directions.

Pop-out phenomenon• A powerful and distinct stimulus

demands our attention• We don’t choose to see them, can’t

ignore it• A type of automatic processing

Automatic processing Controlled processing

Stroop Effect

• Our brain can process information faster when it is presented in the way we expect it

• When too many areas of our brain are active, we have a pause in our processing

• Try this…http://faculty.washington.edu/chudler/java/ready.html

Name the color of the font

AP stuff

• Stimulus attention– Selective attention (cock-tail party)– Stimulus discrimination– Habituation

• Thresholds– Absolute (detectable greater than 50%

of time)– Subliminal (detectable less than 50% of

time)– Just noticeable difference (Weber’s Law)

• It’s a proportion of the original stimulus

Vision

Types of Transduction Light and Sound Characteristics Parts of the eye The process of vision Cells within the retina Shape Detectors and Feature

Detectors Theories of vision

Transduction

In sensation, transformation of stimulus energy into neural impulses.

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

understand(the rods and cones in the retina)

Auditory/Acoustic transduction: Conversion of sound waves into neural impulses (the cilia in the cochlea)

Light Characteristics

1. Wavelength (hue/color)

2. Intensity (brightness)3. Saturation (purity)

Wavelength (Hue)

Hue (color): dimension of

color determined by wavelength of

light.

Wavelength the distance from

the peak of one wave to the peak of the

next.

Intensity (Brightness)

Intensity Amount of energy in a

wave determined

by amplitude; related to perceived

brightness.

The Eye

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 opening (pupil) for light.

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

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

The LensLens: Transparent

structure behind 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.

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.

Fovea

Retina

Retina: The light-sensitive inner surface of the eye, containing

receptor rods and cones plus layers of other

neurons (bipolar,

ganglion cells) that process

visual information.

Bipolar & Ganglion Cells

Bipolar cells receive messages from thephotoreceptor cells(rods and cones) and transmit those messages to ganglion cells which have long axons that areintertwined and form the optic nerve.

Optic Nerve, Blind Spot & Fovea

http://www.bergen.org

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

Test your Blind Spot

Use your textbook. Close your left eye, and with the right eye fixate on the black dot.

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

disappear due to blind spot.

Or, take a piece of paper, roll it up, look through it with one eye and bring your opposite hand next to the paper. There

should be a hole in your hand!!!!(thanks Emilie B.)

Photoreceptors

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

Why don’t they see which color it is?

Feature Detection

Nerve cells in the visual cortex respond to specific features, like edges, angle, and

movement.

Feature detectors allow us to see the lines, motion, curves of this power point slide

What happens when you overwhelm these feature detectors?

Watch the center of the spiral…

Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes,

faces, chairs and houses.

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Perception in Brain

Our perceptions are a combination of sensory (bottom-up) and cognitive (top-

down) processes.

Visual Information Processing

Processing of several aspects of the stimulus simultaneously is called parallel processing.

The brain divides a visual scene into subdivisions such as color, depth, form and

movement etc.

Watch the car video closely and note the different forms of processing that are occurring

simultaneously…

2 Theories of Color Vision

Trichromatic theory: Based on behavioral experiments, Young-Helmholtz suggested

that retina contains three receptors sensitive to red, blue and green colors.

Color Blindness

Genetic disorder in which people are blind to green or red colors supports Trichromatic

theory.

Opponent Process Theory

Gaze at the middle of the flag for about 30seconds…

• As our receptor cells sense colors in our environment, the cones are also firing the opponent (opposite) color

BlackWhite RedGreen BlueYellow

Afterimage Effect

Dark adaptation

• The process by which the rods and cones adjust to changes in levels of light

• Rods are more sensitive to light and so take longer to fully adapt to the change in light

• The fovea is blind to dim light (due to its cone-only array) and the rods are more sensitive

• Insufficient adaptation to dark environment, called “night blindness”.

Color Constancy

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

context changes color of an object may look different.

R. B

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AP stuff…

• Cornea-pupil-lens-retina-photoreceptors-bipolar-ganglion-optic nerve-visual cortex

• Photo transduction takes place in the rods (light) and cones (color)

• Fovea is the point of focus (what happens if..)

• Why a blind spot?• Real image and virtual image

(WOW!)• Remember frequency and amplitude

Hearing

Parts of the Ear and the hearing process

Theories of audition Hearing loss

The Stimulus Input: Sound Waves

Sound waves are composed of compression and rarefaction of air molecules.

Acoustical transduction: Conversion of sound waves into neural impulses in the cilia (hairs

cells) of the inner ear.

Sound Characteristics

1. Frequency (pitch)2. Intensity

(loudness)3. Quality (timbre)

Frequency (Pitch)

Frequency (pitch):

Dimension of frequency

determined by wavelength of

sound.

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

next.

Intensity (Loudness)

Intensity (Loudness): Amount of

energy in a wave determined by

amplitude relates to perceived

loudness.

Loudness of Sound

70dB

120dB

Richard K

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Quality (Timbre)

Quality (Timbre): Characteristics of sound from a zither and a guitar allows the ear to

distinguish between the two.

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The EarGuess what, you don’t hear with your ear. You hear with

your …

Outer EarPinna: Collects sounds. Shaped like a funnelAuditory canal: The auditory canal is a tube that connects the pinna and the tympanic membrane (eardrum)

-funnels sound toward eardrum, protects eardrum

Middle EarMiddle Ear: Chamber between eardrum and cochlea containing three tiny bones (“ossicles”-hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

Inner EarInner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular

sacs.Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transduces sound vibrations to

auditory signals.

Process of hearing• 1. Sound waves enter through the pinna

and travel through the auditory canal• 2. The sound waves begin to vibrate the

tympanic membrane (eardrum)• 3. The ossciles of the middle ear (H.A.S.)

move and the stirrup presses on the cochlea’s oval window

• 4. Fluid in the cochlea circulates causes the movement of the cilia along the basilar membrane

• 5. Neural messages travel along the auditory nerve toward the temporal lobe

Video segment on hearing

1

2

3

4

5

Theories of Audition

Place Theory suggests that sound frequencies stimulate basilar membrane at specific places resulting in perceived pitch.Some hairs vibrate when the pitch is low and some when it is high, ----this explains detection of high frequencies

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Theories of AuditionFrequency Theory states that the rate of nerve impulses traveling up the auditory

nerve matches the frequency of a tone, thus enabling us to sense its pitch.

All hairs vibrate but at different speeds --explains detection of low frequencies

SoundFrequency

Auditory NerveAction Potentials

100 Hz200 Hz

Localization of Sounds

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

us localize the sound.

Hearing Loss

Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea. The waves never reach 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.

Hearing Deficits

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

AP info…• Outer ear (pinna) is shaped like a

funnel, auditory canal and ends at tympanic membrane

• Middle (mechanical) ear has ossicles– Hammer, Anvil, Stirrup (pushes on oval

window)• Inner ear has cochlea, basilar

membrane and cilia (acoustic transduction here)

• Mechanical and Sensory neural hearing loss

• Do you still remember frequency and amplitude?

Other Senses

Somasthetic sense Gustatory sense Olfaction sense Kinesthetic sense Vestibular sense

Touch (somasthetic sense)

Sense of touch is a mix of four distinct skin senses- pressure, warmth, cold, and pain.

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Touch

• Receptors are located all over the skin, some areas more concentrated than others

• The sensory cortex located in the parietal lobe receives the information (left side of body=right brain)

• The more sensitive a body part is, the more surface area is given to it in the cortex

Skin Senses

Only pressure has identifiable receptors, all other skin sensations are variations of

pressures, warmth, cold and pain.

Burning hot

Pressure Vibration Vibration

Cold, warmth and pain

Pain

Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. There is a rare disease in which the person feels no pain.

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

Biopsychosocial Influences

Gate-Control Theory

Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates”

that either block pain or allow it to be sensed. The release of endorphins would

close the gate.

Gary C

omer/ PhototakeU

SA.com

Pain Control

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

acupuncture, exercise, hypnosis and even thought distraction.

Taste

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

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

Sweet Sour Salty Bitter Umami(Fresh

Chicken)

Sensory Interaction

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

Smell

Like taste smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 millions receptors to sense smell. Unlike

taste there are many different forms of smells.

Age, Gender and Smell

Ability to identify smell peaks during early adulthood but steadily decline after that. Women are better at detecting odors than

men.

Smell and Memories

Brain region (red) for smell is closely

connected with brain regions (limbic

system) involved with memory, that is

why strong memories are made through the sense of

smell.

Body Position and MovementThe sense of our body parts’ position and movement is called kinesthesis (joints and

muscles). And the vestibular sense (semicircular

canals in inner ear) monitors the head (and body’s) position.

Wire walk over Niagara FallsNeo learning to move his body

Kinesthetic Sense• provides the parietal cortex of the

brain with information on the relative positions of the parts of the body

• describes how much we know about where we are in space and where all of our

parts are in relationship to each other• Our kinesthetic sense helps us move with greater precision, avoid injuries, and be fully present in the moment• Close your eyes and touch the tip of your nose with the tip of your finger

Vestibular Sense (equilibrium)

• Monitors the position of the head in relation to the body, the sensations of body rotation and of gravitation and movement

• Operates based on movement of fluid within the semi-circular canals of the inner ear

• The vestibular system sends signals primarily to the neural structures that control eye movements, and to the muscles that keep a creature upright

• Abnormalities may cause “vertigo”

http://www.neurolearning.com/images/snakeillusion.jpg

Ap stuff…

• Transduction – process by which sensory information is transformed into neural impulses.

• Adaptation – the decreasing response of a sense when they are exposed to continuous stimulation.

• Opponent-process theory – The thalamus of the brain responds to two pairs of colors (red/green and blue/yellow).

• Tri-chromatic theory – Cones in the eye pick up three colors: green, red and blue.

Ap stuff cont…

• Frequency theory – the rate at which nerve impulses reach the brain determine how low the pitch of the sound is. Low pitches have lower frequency. The higher the frequency, the higher the pitch

•  Place theory – The area within the basilar membrane of the cochlea determines how we hear high pitch sounds

More AP info…• Touch- pressure, pain, temperature

(not hot)• Taste and smell are chemical senses

and linked together (flavor), not in the thalamus

• Kinesthetic sense-position of body parts and movement (in joints and muscles)

• Vestibular sense-whole body position, balance (in semi-circular canals of the inner ear)

• Optic-sight• Acoustic-hearing• Olfactory-smell• Gustatory-taste