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Sensation
Sensation a process by which our sensory
receptors and nervous system receive and represent stimulus energy
Perception a process of organizing and interpreting
sensory information, enabling us to recognize meaningful objects and events
SensationBottom-Up Processing
analysis that begins with the sense receptors and works up to the brain’s integration of sensory information
Top-Down Processing information processing guided by higher-
level mental processes as when we construct perceptions drawing
on our experience and expectations
Sensation- Basic Principles
Psychophysics study of the relationship between
physical characteristics of stimuli and our psychological experience of them
Light- brightness Sound- volume Pressure- weight Taste- sweetness
Sensation- ThresholdsAbsolute Threshold
minimum stimulation needed to detect a particular stimulus
usually defined as the stimulus needed for detection 50% of the time
Difference Threshold minimum difference between two stimuli that
a subject can detect 50% of the time just noticeable difference (JND) increases with magnitude
Sensation- Thresholds
When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.
0
25
50
75
100
Low Absolutethreshold
Medium
Intensity of stimulus
Percentageof correctdetections
Subliminal stimuli
Sensation- ThresholdsWeber’s Law- to perceive a
difference between two stimuli, they must differ by a constant proportion
a constant for each sense: light intensity- 8%, weight- 2% tone frequency- 0.3% Just noticable difference has a proportion
to be met in order to sense difference
Weber’s Law
Classic and still identified today but it did not account for extreme values….175 watt and a 200 watt…
Ability to recognize difference diminishes….so in 1860s
Sensation- ThresholdsFechner’s Law- “upgrade” of
Weber’s law includes increase of jnd with extreme
measures/magnitude Adding the relationship of the perceived
magnitude to physical intensity of a stimuli
Same basic idea: ½ pound book in 2lb vs. 60lb backpack 1 voice in chorus of 10 versus 2 in 20
Sensation- Thresholds
Steven’s Power Law - upgrade to Fechner (Fechner’s law didn’t work for pain*, other stimuli)
Strength of a sensation related to the intensity of the stimuli raised to some power
So pain like electric shock you will sense a a small change at higher intensities than at the lower intensities when more may be needed to recognize difference
Fechner
Stevens
Sensation - Thresholds
Note that one of the implications of Steven’s law is that with higher levels of pain you get MORE sensitive!
Sensory adaptation- diminished sensitivity with constant stimulation
Sensation- ThresholdsSignal Detection Theory
predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)
assumes that there is no single absolute threshold detection depends partly on person’s
experienceexpectationsmotivationlevel of fatigue
Sensation- ThresholdsSignal Detection Theory
Assumes TWO things going on: 1. sensitivity to stimulus (physical) 2. response bias – also called decision
criterion (psychological)
Can measure & plot these in a Receiver Operating Characteristic curve (ROC curve)
Vision
Transduction- conversion of one form of energy to another (for us, it’s specifically: converting physical energy to neural impulses)
Properties of light and vision Physical Psychologicalintensity brightnesswavelength hue (color)wave purity saturation
Vision
Wavelength- the distance from the peak of one wave to the peak of the next
Amplitude - the height (strength) of a wave
Hue- perceived “color” of the lightIntensity- amount of energy in a wave
determined by amplitudeSaturation - perceived “purity” of a color
(e.g. pastels have low saturation)
Vision- Spectrum of Electromagnetic Energy (quantum particle/waves)
Vision- Physical Properties of Waves
Short wavelength=high frequency(bluish colors, high-pitched sounds)
Long wavelength=low frequency(reddish colors, low-pitched sounds)
Great amplitude(bright colors, loud sounds)
Small amplitude(dull colors, soft sounds)
VisionPupil- adjustable opening in the
center of the eye
Iris- a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening
Lens- transparent structure behind pupil that changes shape to focus images on the retina
Vision
VisionAccommodation
change in shape of lens focus near objects
Retina inner surface of eye light sensitive contains rods and cones layers of neurons beginning of visual information
processing
Vision
Acuity- the sharpness of visionNearsightedness
nearby objects seen more clearly lens focuses image of distant objects in
front of retinaFarsightedness
faraway objects seen more clearly lens focuses near objects behind retina
Retina’s Reaction to Light- Receptors
Cones near center of retina (fovea) fine detail and color vision daylight or well-lit conditions
Rods peripheral retina detect black, white and gray twilight or low light
Saccades - quick eye movements
Retina’s Reaction to Light
Bipolar cells- neurons that combine info from multiple receptors
Ganglion cells – neurons that combine info from multiple bipolar cells.
Optic nerve – bundle of axons of the ganglion cells that carry info from retina to brain.
Vision- Receptors
Receptors in the Human Eye
Cones Rods
Number
Location in retina
Sensitivity in dim light
Color sensitive? Yes
Low
Center
6 million
No
High*
Periphery
120 million
*Why pirates wore eyepatches? Arrrr…
Retina’s Reaction to Light
Optic nerve- nerve that carries neural impulses from the eye to the brain
Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there
Fovea- central point in the retina, around which the eye’s cones cluster
Pathways from the Eyes to the Visual Cortex
Vision- Stabilized Images on the Retina
Retina’s Reaction to Light
Receptive fields – regions in which receptors respond to light
Lateral inhibition – receptor (or neuron) making it’s neighbors less sensitive Helps in things like edge detection
Visual Information Processing
Feature Detectors neurons in the
visual cortex respond to specific features
shape angle movement
Stimulus
Cell’s responses
Visual Information Processing
Parallel Processing simultaneous processing of
several dimensions through multiple pathways
color motion form depth
Visual Information Processing
Scene
Retinal processing:Receptor rods andconesbipolar cells
ganglion cells
Feature detection:Brain’s detector cells
respond to elementaryfeatures-bars, edges, or
gradients of light
Abstraction:Brain’s higher-level cells
respond to combinedinformation from
feature-detector cells
Recognition:Brain matches the
constructed image withstored images
Visual Information Processing
Neural pathways (multiple!) Optic nerve through optic chiasm
(crossover), becomes the optic “tract” then…
Primary visual cortex (striate cortex) then splits into…
The “what” path (thru temporal lobes) The “where” path (up into parietal lobes)
Visual Information Processing – Color vision
Trichromatic (three color) Theory The Young–Helmholtz theory three different retinal color receptors
sensitive toredgreenBlue
Visual Information Processing – Color vision
But Tri-chromatic didn’t explain afterimages or color-blindness! So…
Opponent Process Theory Black-white receptors (for brightness &
saturation) Red-green receptors (for hue) Blue-yellow receptors (for hue)
Opponent Process- Afterimage Effect
Color-Deficient Vision
People who suffer red-green blindness have trouble perceiving the number within the design
Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable color vision“ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black
Visual Information Processing – Color vision
So who’s right??? Turns out they’re both right:
Tri-chromatic theory works in the retina Opponent process works in the higher visual
processing parts of the brain Together they explain what we know about
color vision quite well.
Audition
Auditionthe sense of hearing
Properties of sound and hearing Physical Psychologicalintensity loudnesswavelength pitchwave purity timbre (tone)
Audition
Frequencythe number of complete wavelengths
that pass a point in a given time Pitch
a tone’s highness or lownessdepends on frequency
Timbre - tonal quality; “richness”
The Intensity of Some Common Sounds
Audition- The EarOuter Ear
Auditory Canal Eardrum
Middle Ear hammer anvil stirrup
Inner Ear oval window cochlea basilar membrane hair cells
Audition
Place Theory the theory that links the pitch we hear
with the place where the cochlea’s membrane is stimulated
Frequency Theory the theory that the rate of nerve
impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch
Audition
So who’s right? They’re both probably right: At low frequencies: frequency
theory At high frequencies: place theory At middle frequencies: both
How We Locate Sounds
How we locate sounds
Two cues: Differences between the two ears
in loudness Differences in the arrival time at
the ears
Audition
Conduction Hearing Loss hearing loss caused by damage to the
mechanical system that conducts sound waves to the cochlea
Nerve Hearing Loss hearing loss caused by damage to the
cochlea’s receptor cells or to the auditory nerve
Audition Older people tend to hear low frequencies well
but suffer hearing loss for high frequencies
1time
10times
100times
1000times
32 64 128 256 512 1024 2048 4096 8192 16384
Frequency of tone in waves per second
Low Pitch High
Amplitude required forperception relative to 20-29 year-old group
Touch
Skin Sensations pressure
only skin sensation with identifiable receptors
warmth cold pain
PainGate-Control Theory
theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain
“gate” opened by the activity of pain signals traveling up small nerve fibers
“gate” closed by activity in larger fibers or by information coming from the brain
TasteTaste Sensations
sweet sour salty bitter
Sensory Interaction the principle that one sense may influence
another as when the smell of food influences its taste
Smell
Receptor cells inolfactory membrane
Nasal passage
Olfactorybulb
Olfactorynerve
Age, Sex and Sense of Smell
Women
Men
10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99Age Group
4
3
2
0
Numberof correct
answers
Women and young adults have best sense of smell
SmellLess important in humans than
animals but we still can detect:Pheromones
Smell-communicated chemicals secreted by organisms
People can often identify gender by smell of sweaty hands or articles of clothing!
Body Position and Movement
Kinesthesis the system for sensing the position
and movement of individual body parts
Vestibular Sense the sense of body movement and
position including the sense of balance
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