Sensation & perception
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Transcript of 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