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Sensation Chapter and Perception
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What is Sensation and
PSensation process where the senses pick up visual,
erception?
auditory, and other sensory stimuli and transmit them to
the brain.
Perception sensory information that is actively
organized and interpreted by the brain.
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Thresholds
Absolute threshold minimum amount of sensory
stimulation that can be detected 50% of the time
E.g. a candle flame 30 miles away on a clear night
Ticking watch 20 feet away
Difference threshold measure of smallest increase or
decrease of a physical stimulus that produces a different
sensation 50% of time
Just noticeable difference (JND)
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Webers Law
Webers law JND depends on a percentage of change in
a stimulus rather than a fixed amount
2% weight change
.33% pitch change
20% for taste
Impacted if you lose a sense
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Transduction and
ASensory receptors specialized cells in sense organs that
daptation
detect specific kinds of stimuli
Convert sensation (transduction) into neural impulses
Transduction converts information into electrochemical
language
Sensory adaptation we become use to a sensation and
stop noticing it
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Vision
Our visual spectrum is relatively small (red to violet)
We see the reflection of electromagnetic waves
White represents a reflection of all the waves
Black is the absence of the reflected light
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Rods and Cones
Rods helps eyes respond to low levels of light and
shaped like a cylinder
120 million
Cones cone shaped cells that allow us to see color and
fine detail in good light
6 million
Rhodopsin - chemical that helps us adapt to light levels
Opsin and retinal
Break apart in bright light
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Major Parts of the Eye
Vision Problems
Presbyopia old eyes
Lens stops flexing
Myopia nearsighted
Lens focuses far images in front of retina
Cant see objects that are far away
Hyperopia Far sighted
Focuses near objects behind the retina
Cant see near objects
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Figure 3.5 Pathways in the Human Visual System
Color Vision
Hue dimension of light that refers to the specific color
Saturation purity of color which is the degree to which
the light waves producing it are of the same wavelengths
Brightness intensity of light energy
Color blindness inability to distinguish certain colors
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Theories of Color Vision
Trichromatic theory 3 retinal cones (red, blue, and
green)
Opponent-process theory 3 kinds of cells respond by
increasing and decreasing and firing rates when see
different colors
Both theories explain different phases of color vision
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Hearing
We hear by waves traveling through a medium
Boyle (1660) found that if you remove air and make a
vacuum, sound cant be heard
Frequency cycles completed by a sound wave per
second (hertz)
20 Hz to 20,000 Hz
Amplitude measure of loudness
Decibels (dB) unit of loudness
0 dB is softest sound that can be heard in a quiet
environment
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Hearing
Audition sensation and process of hearing
Outer ear pinna, auditory canal
Focuses sound but could live without it
Sound travels through canal
Gives sense of direction
Middle ear eardrum, ossicles, oval window
Transfers vibration
3 smallest bones (hammer, anvil, stirrup) amplify sound
Oval window vibrates to transfer sound
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Hearing
Inner Ear cochlea, semicircular canals, hair cells,
auditory nerve
Cochlea is a fluid-filled snail shaped structure
Transfers waves through fluid to vibrate hair cells
Auditory nerve receives signal and passes it on to brain
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The Hearing Process
Theories of Hearing
Place theory (Helmholtz) pitch is determined by place
along basilar membrane where vibration occurs
Frequency theory frequency of hair cell vibrations
determine pitch
Above 1000Hz would be too fast for neurons to fire
Frequency theory explains low tones and place theory
explains high tones
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Hearing Loss
1 in 1000 infants are born with moderate to severe hearing
loss;
40% of older adults experience hearing loss
Conduction deafness affects eardrum or bones in middle
ear
Sensorineural hearing loss damaged cochlea or auditory
nerve
Hearing aid or choclear implants
Excessive noise can be damaging chronic exposure to
above 90 dB
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Smell
Capable of smelling 10,000 different odors
Can only smell gases
Intensity of smell is determined by number of neurons
firing at same time
Olfactory neurons only last for about 1 month and
constantly renew
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Smell
Smell and Memory
Smell, emotion, and memory are linked
Bypasses hippocampus
Peak memory between 6 and 10 years old
Alzheimers and Dementia
Loss of olfactory function seems to predict onset of
dementias
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Pheromones
Chemicals excreted by humans and animals that affect
behavior
Important for bonding
Mark territories
Signals sexual readiness (humans and animals)
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Taste
Gustation sense of taste
5 tastes
Sweet, sour, salty, bitter, and umami
Receptors for each on all parts of tounge
Also in cheeks, lips, throat, and tonsils
Three tasters
Nontasters cant taste certain bitter and sweet compounds
Supertasters taste compounds with more intensity
May eat less salad due to bitterness
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Touch
Touch is an important sense
Premature babies weight gain 47% faster if massaged for 15
minutes a day
Tactile information relayed to brain when skin is
depressed
Two-point threshold distance where you can feel two
separate touches
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Pain
Gate-control theory area of spinal cord acts as gate that
either blocks or transmits pain to the brain
Pain transmitted through slow conducting nerve fibers
Fast conducting nerve fibers can block sensations of pain
Amygdala is changed by chronic pain
Endorphins bodys chemicals to block pain
Runners high & sex
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Balance and Movement
Kinesthetic sense information about parts of body in
relation to each other
Incorporates visual information with sensory information
from joints and muscles
Vistibular sense detects information about bodys
orientation in space
Semicircular canals fluid filled tubular canals in the inner
ear
Senses rotation of body
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Perceptual Organization
Gestalt German word that roughly refers to the whole
form, pattern, or configuration that a person perceives
Whole is greater than sum of parts
Rarely do we separate world into small parts
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Gestalt Principles of Grouping
Similarity objects that have similar characteristics are grouped together
Proximity objects that are close together are perceived as belonging together
Continuity figures or objects are perceived as belonging together if they
appear to form a continuous pattern
Closure figures with gaps in them are perceived as complete
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Education, Inc. All rights
Perceptual Constancy
Perceptual constancy we understand that objects dont
literally grow or shrink as they move towards us or away
from us
Shape constancy object shape is constant regardless of
view
Brightness constancy brightness is constant no matter
the intensity of light
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Depth Perception
Ability to perceive the world in 3-dimensions and judge
distance accurately
Convergence (eyes turning inward)
Binocular disparity - difference between two retinal
images
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Monocular Depth Cues
Interposition
When one object partly blocks your view of another, you perceive the partially
blocked object as farther away
Linear perspective
Parallel lines that are known to be the same distance apart appear to grow closer
together, or converge, as they recede into the distance
Relative Size
Larger objects are perceived as being closer to the viewer, and smaller objects as
being farther away
Texture gradient
Near objects appear to have sharply defined textures, while similar objects
appear progressively smoother and fuzzier as they recede into the distance
Atmospheric perspective
Objects in the distance have a bluish tint and appear more blurred than objects
close at hand
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Monocular Depth Cues
Shadow or shading
When light falls on objects, they cast shadows
You can distinguish bulges from indentations by the shadows they cast
Motion parallax
When riding in a moving vehicle and look out the side window, the
objects you see outside appear to be moving in the opposite direction
The objects also seem to be moving at different speeds those
closest to you appear to be moving faster than those at a distance
Objects very far away, such as the moon and the sun, appear to move
in the same direction as the viewer
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Motion
Real Motion tied to movement of real objects through
space
Edges of retina
Kinesthetic sense is important too
Based on a sense of stability
Apparent motion Phi Phenomenon (Wertheimer, 1912)
Perception of light moving
Stroboscopic motion (TV or movie motion)
Autokinetic illusion perception of something moving 33
Puzzling Perceptions
Ambiguous and Impossible Figures
q Sum of sensory parts conveys dramatically different perceptions of an
object or stimulus
q Perceptual systems are puzzled and view objects first one way, and then
totally differently
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Education, Inc. All rights
Influences on Perception
Attention
q Process of sorting through sensations and selecting some for further processing
q Some sensations are automatic requiring minimal mental effort
q Inattentional blindness
q Focus is shifted from one object to another
q Changes in objects not receiving direct attention are not noticed
q Cocktail party phenomenon
q When you hear your name, focus follows due to assumption that other
meaningful information will follow
q Focus
q Information that receives focus is remembered while other stimulation received at
same time is lost
q
Hearing words spoken into both ears at same time; only words that receive
focus of attention are recalled Pearson
Copyright 2011
Influences on Perception
q Prior knowledge
q Enhances or leads to perceptual errors
q Bottom-up processing
q Received stimulus are combined with prior knowledge to make
inferences about received patterns
q Top-down processing
q Previous experience and conceptual knowledge are used to recognize
stimuli and logically deduce individual components of that whole
q Perceptual set
q Expectation of what will be perceived
q Can affect what actually is perceived
Copyright 2011 Pearson