Sensation Detection of external stimuli Response to the stimuli Transmission of the response to...
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Transcript of Sensation Detection of external stimuli Response to the stimuli Transmission of the response to...
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
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
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
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
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
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
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!
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
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
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
The Necker Cube
• The cubes seem to shift and another side seems closer to
you.
• Then it shifts back again
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