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Sensation&
PerceptionChapters 5&6
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- 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- 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
Receptors
Environmental information (stimuli) exist in many forms:
•Air vibrations, gases, chemicals, tactile pressures
•The body receives these forms through specialized cells:
•Receptor cells
•E.g., taste buds
Receptors
Receptor sensitivity is subject to change
•Sensory adaptation
•Decline in receptor activity when stimuli are unchanging
•E.g., noticing a bad smell at first
Receptors
•Habituation
•Decline in sensory sensitivity at neural level due to repeated stimulation
•Different from adaptation since responsiveness can reappear if stimulation level increases or decreases
Vision- Stabilized Images on the Retina
Vision
Transduction- conversion of one form of energy to another
Wavelength- the distance from the peak of one wave to the peak of the next
Hue- dimension of color determined by wavelength of light
Intensity- amount of energy in a wave determined by amplitude brightness loudness
Vision- Spectrum of Electromagnetic Energy
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 that 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
Vision
Farsighted Nearsighted Normal Vision Vision Vision
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
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
Visual Information Processing
Feature Detectors neurons in the
visual cortex respond to specific features
shape angle movement
Stimulus
Cell’s responses
How the Brain Perceives
Illusory Contours
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
Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors
redgreenblue
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
Opponent Process- Afterimage Effect
Audition
Auditionthe sense of hearing
Frequencythe number of complete wavelengths
that pass a point in a given time Pitch
a tone’s highness or lownessdepends on frequency
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
Taste
4 basic sensations – sweet, sour, salty and bitter
All taste is a mixture of these
Taste is a chemical sense
Taste budsSensory interaction
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
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
Pain Control
Drugs, surgery, acupuncture, electrical stimulation, massage, exercise, hypnosis, relaxation training, and thought distraction
LamazePsychological aspects of pain
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
Vestibular sense - the sense of body movement and position, including the sense of balance•Semicircular canals – pretzel •Vestibular sacs – connect the canals to the cochlea•Move when we move our head•Hairlike receptors
Sensory Restriction Kissing Aphasia – ability to comprehend language Loss of a sense 1st experiments – Sensory Deprivation – disoriented,
hallucinations Sensory restriction does not disturb most people It reduces stress More open to positive influence Behavior modification REST – restricted environmental stimulation therapy Bottom-Up Chapter 6 Top-Down
If you had to lose one sense, which would it be?
If you could only have one, which would it be?
Perception
Selective Attention focus of conscious awareness on a particular stimulus
Perceptual Illusions
Perceptual Organization- Gestalt
Visual Capture tendency for vision to dominate
the other sensesGrouping
the perceptual tendency to organize stimuli into coherent groups
Perceptual Organization- Gestalt
Gestalt- an organized whole tendency to integrate pieces of information into
meaningful wholesGrouping Principles
proximity- group nearby figures together similarity- group figures that are similar continuity- perceive continuous patterns closure- fill in gaps connectedness- spots, lines and areas are seen
as unit when connected
Perceptual Organization
Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground)
Perceptual Organization- Grouping Principles
Perceptual Organization- Grouping Principles
Gestalt grouping principles are at work here.
Perceptual Organization-Depth Perception
Depth Perception ability to see objects in three dimensions allows us to judge distance
Binocular cues retinal disparity
images from the two eyes differ closer the object, the larger the disparity
convergenceneuromuscular cuetwo eyes move inward for near objects
Perceptual Organization-Depth Perception
Visual Cliff
Perceptual Organization-Depth Perception
Monocular Cues relative size
smaller image is more distant interposition
closer object blocks distant object relative clarity
hazy object seen as more distant texture coarse --> close
fine --> distant
Perceptual Organization-Depth Perception
Relative Size
Perceptual Organization-Depth Perception
Perceptual Constancy
Perceptual Constancy perceiving objects as unchanging
despite changes in retinal imagecolorshape size
Perceptual Organization
Perceptual Organization-Muller-Lyer Illusion
Perceptual Organization- Size-Distance Relationship
Perceptual Organization-Brightness Contrast
Perceptual Interpretation
Perceptual Adaptation (vision) ability to adjust to an artificially displaced visual fieldprism glasses
Perceptual Set a mental predisposition to perceive one thing and not another
Perceptual Set-Schemas
What you see in the center is influenced
byperceptual set
Perceptual Set-Schemas
Flying Saucers or Clouds?
Perception without Sensation?
Extrasensory Perception controversial claim that perception can occur
apart from sensory inputtelepathyclairvoyanceprecognition
Parapsychology the study of paranormal phenomena
ESPpsychokinesis
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