Sensation & perception

SENSATION &

PERCEPTION

How do we sense our worlds?

Sensation Detection of external stimuli Response to the stimuli Transmission of the response to the brain

Perception Processing, organizing and interpreting

sensory signals Internal representation of the stimulus

The Sensing Process

Stimulus

Sensation Sensory receptors in the eye

detect the stimulus

The Sensing Process Sensory Coding

Stimulus is transduced (translated into chemical & electrical signals that are sent to the brain)

Perception The brain processes the neural

signals and constructs a representation of the green light – a signal to go

THE STIMULI, RECEPTORS &

PATHWAYSThe 5 Senses

Taste Stimuli

Molecules on the tongue

Receptors Cells in taste buds

on the tongue Pathways to the

brain Portions of facial,

glossopharyngeal, and vagus nerves

Smell Stimuli

Molecules on mucus membranes in the nose

Receptors Sensitive ends of

olfactory neurons Pathways

Olfactory nerves

Touch Stimuli

Pressure on the skin Receptor

Sensitive ends of touch neurons in skin

Pathway Cranial nerves for

touch above the neck, spinal nerves for touch elsewhere

Hearing Stimuli

Sound waves Receptors

Pressure-sensitive hair cells in the cochlea of the inner ear

Pathways Auditory nerve

Vision Stimuli

Light waves Receptor

Light sensitive rods and cones in the retina of the eye

Pathway Optic nerve

SENSORY THRESHOLDSSensory organs

constantly acquire

information from the environment

Absolute Threshold The minimum intensity of stimulation that

must occur before you experience a sensation

Approximate Absolute Sensory Threshold Taste – 1 tsp. of sugar in 2 gallons of water Smell – 1 droplet of perfume in a standard size room Touch – a fly’s wing falling on your cheek Hearing – the tick of a clock at 20ft in quiet conditions Vision – a candle flame seen at 30 miles on a dark,

clear night

Difference Threshold The just noticeable difference between

2 stimuli Minimum amount of change required for

a person to detect a difference

Example: If you’re reading a book and watching TV, a

commercial comes on that is louder than the show – you look up and notice something has changed

The DT is the minimum change in volume required to detect a difference

SIGNAL DETECTION THEORY

SDT

SDT Detecting a stimulus requires

making a judgment about its presence or absence

The detection of a faint stimulus requires a judgment

Example A hearing test Person wears headphones and is

told to raise their hand when they hear the tone in that ear

Sensory Adaptation A decrease in sensitivity

to a constant level of stimulation

Example You are studying and your

neighbor starts mowing their lawn

After a few minutes the noise seems to blend in or fade into the background

HOW WE EXPERIENCE THE SENSE OF SOUND

Hearing The 2nd sense to vision Sound waves – pattern of

changes in air pressure Amplitude – loudnessFrequency – pitch

Process of Hearing Sound waves arrive at the outer ear Travel down the auditory canal to the

eardrum Then to the middle ear Sound waves make the eardrum vibrate Vibrations transfer to 3 tiny bones

Hammer Anvil Stirrup

Then to the auditory nerve

HOW WE EXPERIENCE THE SENSE OF SIGHT

Vision Most important

source of knowledgeDoes a place look safe or dangerous?

Does a person look friendly or hostile?

Process of Seeing Light first passes through the cornea

(transparent outer layer) Cornea focuses incoming light, which enters

the lens Forms an image on the retina (thin inner

surface of the back of the eyeball) THE RETINA IS THE ONLY VISIBLE PART OF

THE BRAIN OUTSIDE THE SKULL! Pupil – dark circle at the center

Contracts – gets smaller Dilates – gets larger

Process of Seeing Iris – eye color Behind the iris, muscles change the

shape of the lens Lens – focuses images through

accomodation

2 Types of Cells in the Retina

Rods Respond to extremely low levels of light Used primarily in night vision

Cones Respond in bright levels of light Used for seeing color and detail

Color Determined by wavelength An object appears to be a particular

color because of the wavelength it reflects

Color is always a product of our visual system; there is no color in the physical world!

Color Spectrum

ROYGBIV

Trichromatic Theory 3 different types of cones that are sensitive to

different wavelengths

1. Short (blue-violet)

2. Medium (yellow-green)

3. Long (red-orange)

Opponent-Process Theory Some colors seem to be opposites

Stare at a red image – see a green afterimage

Stare at a green image – see a red afterimage

Stare at a blue image – see a yellow afterimage

Stare at a yellow image – see a blue afterimage

3 Dimensions of Color Hue

Distinctive characteristics of a color Ex. – blue, light blue, navy blue, turquoise

Saturation Color’s purity, vividness

Ex. – lime green, fluorescent yellow Brightness

Perceived intensity Two of the same exact colors can be perceived

differently in different light

GATE CONTROL THEORY

Pain Brain regulates the experience of pain

Producing it Suppressing it

Depends on biological, psychological, and cultural factors

Gate Control Theory of Pain

For a person to experience pain:

Pain receptors must be activated A neural gate in the spinal cord must allow the

signals through to the brain Eventually, the “gate” closes and no more

pain signals reach the brain

Visual Illusions Illusions are tools used by psychologists

to determine how the brain understands information

GESTALT PSYCHOLOGY“Organized whole”

Figure & Ground

Proximity & Similarity

Closure

Continuation

DEPTH PERCEPTION

Depth Cues Binocular

Both eyes

Monocular Each eye separately

1. Accommodation – change in the shape of the lens that varies with distance (1 eye)

2. Convergence – the way the eyes rotate inward and outward with changes in distance (2 eyes)

3. Binocular disparity – difference between the images provided by each eye

Figure and Ground 3 Principles

1. The figure is more “thinglike” and more memorable than the ground

2. The figure is seen as being in front of the ground

3. The ground is seen as unformed material and seems to extend behind the figure

Monocular Depth Perception

Occulsion A near object blocks an object that is farther away

Relative Size Far-off objects project a smaller retinal image than

close objects Linear perspective

Parallel lines appear to converge in the distance Texture gradient

Shows depth or looks dense Position relative to the horizon

Objects below the horizon that appear higher in the visual field are perceived as being farther away

Perception of Motion Different kinds of movement:

A figure moving against a stationary background

Objects at rest against a moving background Objects moving at different speeds in relation

to each other Observer’s own movements in relation to

his/her surroundings

Induced movement perception of movement of an object that is

not moving

ILLUSIONS

Muller-LyerWhich line appears longer?

Ponzo Railroad Track Illusion

Which of the two horizontal lines on the track appear longer?

The Necker Cube

• The cubes seem to shift and another side seems closer to you.

• Then it shifts back again

The Boring Figure

• Designed by E.G. Boring

• Ambiguous figure

• Young girl/old woman

The Ames Room

Albert Ames Appears to be a

normal room Actually shaped so

the left corner is almost twice as far from the viewer as the right corner

The viewer perceives the nearer person as being much larger than the other, although both are exactly the same height

What do you see?

Focus on the Center DotMove your head backward & forwards