Sensing and Perceiving
Sensing and Perceiving
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We Experience Our World Through Sensation
Seeing
Hearing
Tasting, Smelling, and Touching
Accuracy and Inaccuracy in Perception
Sensing and Perceiving
Sensation
• stimulation of sense organs
Transduction
• conversion of stimuli detected by receptor cells to electrical impulses
transported to the brain
Perception
• organization and interpretation of sensations
We Experience Our World Through Sensation
We Experience Our World Through Sensation
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Learning Objectives
1.
Review and summarize the capacities and limitations of human sensation.
2.
Explain the difference between sensation and perception and describe how psychologists
measure sensory and difference thresholds.
Measuring Sensation
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Psychophysics
– branch of psychology that studies the effects of physical stimuli on sensory perceptions
and mental states
– founded by the German psychologist Gustav Fechner in the 19th century
Measuring Sensation
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Absolute Threshold
– the intensity of a stimulus that allows
an organism to just barely detect it
Measuring Sensation
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Signal Detection Analysis
– technique used to determine the perceiver’s ability to separate true signals from
background noise
– yields two measures:
• sensitivity – the true ability to detect the presence of absence of signals
• response bias – behavioral tendency to respond ‘yes’
Measuring Sensation
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Possible trial outcomes in a signal detection experiment. Correct rejections and hits are
accurate responses; misses and false alarms are errors.
Measuring Sensation
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Difference Threshold
– the change in a stimulus that can just barely be detected by the organism
– also called the just noticeable difference, or jnd
Weber’s Law
– the just noticeable difference is a constant proportion of the original intensity of the
stimulus
Influence Without Awareness
subliminal
stimuli
blindsight
perception
without
awareness?
Subliminal Stimuli
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Stimuli below the absolute threshold may
have some effect on behavior.
The influence of subliminal advertising is
weak, though.
Blindsight
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Visual cortex damage may render people
unable to consciously report on visual
stimuli, even though they can answer
questions about what they are seeing.
We Experience Our World Through Sensation
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Key Takeaways
– Sensation is the process of receiving information from the environment through our
sensory organs. Perception is the process of interpreting and organizing the incoming
information in order that we can understand it and react accordingly.
– Transduction is the conversion of stimuli detected by receptor cells to electrical impulses
that are transported to the brain.
– Although our experiences of the world are rich and complex, humans – like all species –
have their own adapted sensory strengths and sensory limitations.
– Sensation and perception work together in a fluid, continuous process.
We Experience Our World Through Sensation
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Key Takeaways, continued
– Our judgments in detection tasks are influenced by both the absolute threshold of the
signal as well as our current motivations and experiences. Signal detection analysis is used
to differentiate sensitivity from response biases.
– The difference threshold or just noticeable difference is the ability to detect the smallest
change in a stimulus about 50 percent of the time. According to Weber’s law, the just
noticeable difference increases in proportion to the total intensity of the stimulus.
– Research has found that stimuli can influence behavior even when they are presented
below the absolute threshold (that is, subliminally). The effectiveness of subliminal
advertising, however, has not been shown to be of large magnitude.
Seeing
Seeing
Learning Objectives:
1.
Identify the key structures of the eye and the role they play in vision.
2.
Summarize how the eye and the visual cortex work together to sense and perceived the
visual stimuli in our environment, including processing colors, shape, depth, and motion.
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Vision detects electromag-netic radiation.
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Only a small portion of the electromagnetic spectrum is seen as visible light.
Seeing: Perceiving Depth
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Depth Cues: messages from our bodies and the environment that tell us about space and
distance; may be monocular (requiring one eye) or binocular (requiring two eyes)
binocular depth cues
retinal disparity
convergence
accommodation
the two eyes receive
different images
inward turning of the
eyes to focus on objects
changes in curvature of
the lens
Seeing: Perceiving Depth
Seeing: Perceiving Depth
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Figure-Ground: Some fence posts seem
more distant because they are higher up in
the picture.
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Relative Size: The smaller –looking cars
appear more distant than do the largerlooking ones.
Seeing: Perceiving Depth
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Linear Perspective: We know that the
tracks are parallel. As they appear to
converge, we determine that they are
farther away.
Light and Shadow: We see the images as
extending and indented according to their
shadowing. If we invert the picture, the
images will reverse.
Seeing: Perceiving Depth
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Interposition: Because the blue star
covers the pink bar it is seen as closer than
the yellow moon which does not.
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Aerial Perspective: The clouds appear
hazy and thus seem distant.
Seeing: Perceiving Motion
Beta Effect
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Perception of motion that occurs when
different images are presented in
succession
Used in movies to create the impression of
motion
Phi Phenomenon
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We perceive motion based on the
appearance and disappearance of adjacent
objects.
Identified by the Gestalt psychologists
Seeing
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Key Takeaways
– Vision is the process of detecting the electromagnetic energy that surrounds us. Only a
small fraction of the electromagnetic spectrum is visible to humans.
– The visual receptor cells on the retina detect shape, color, motion and depth.
– Light enters the eye through the transparent cornea, and passes through the pupil at the
center of the iris. The lens adjusts to focus the light on the retina, where it appears
upside down and backward. Receptor cells on the retina are excited or inhibited by the
light and send information to the visual cortex through the optic nerve.
– The retina has two types of photoreceptor cells; rods, which detect brightness and respond
to black and white, and cones that respond to red, green and blue colors. Color blindness
occurs when people lack function in the red or green-sensitive cones.
Seeing
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Key Takeaways, continued
– Feature detector neurons in the visual cortex help us recognize objects, and some neurons
respond selectively to faces and other body parts.
– The Young-Helmholtz Tri-Chromatic Color Theory proposes that color perception is the
result of the signals sent by the three types of cones, whereas the Opponent Process Color
Theory proposes that we perceived color as three sets of opponent colors; red-green,
yellow-blue, and white-black.
– The ability to perceive depth occurs through the result of binocular and monocular depth
cues.
– Motion is perceived as a function of the size and brightness of objects. The beta effect
and the phi phenomenon are examples of perceived motion.
Hearing
Hearing
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Learning Objectives:
1.
Draw a picture of and label the key structures and functions of the ear and the role they
play in hearing.
2.
Describe the process of transduction in hearing.
The Ear
frequency
wavelength of the sound wave
humans can detect wavelengths from
20 Hz -20,000 Hz
pitch
perceived frequency of a sound
higher frequency = higher pitch
The Ear
amplitude
height of the sound wave
humans can detect wavelengths from 20 Hz 20,000 Hz
loudness
degree of sound volume
larger waves= louder
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Sounds in Everyday Life
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The human ear can comfortably hear
sounds up to 80 dB.
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Prolonged exposure to sounds above 80dB
can cause hearing loss.
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The Ear
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Sound waves enter the outer ear and are
transmitted through the auditory canal to
the eardrum.
The resulting vibrations are moved by the
ossicles into the cochlea, where they are
detected by hair cells and sent to the
auditory nerve.
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The Ear
1. pinna
draws in sound
waves
2. sound waves
strike tympanic
membrane
3. vibrations
relayed through
ossicles
6. hair cells
bend
5. fluid in
cochlea moves
4. oval window
vibrates
The Ear
Frequency Theory of Hearing
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As the pitch of a sound wave increases,
nerve impulses of a corresponding
frequency are sent to the auditory nerve.
– Neurons cannot fire fast enough to
code pitches as high as we can hear.
Place Theory of Hearing
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Different areas of the cochlea respond to
different frequencies.
– Higher tones excite areas at the
opening of the cochlea near the oval
window.
– Lower tones excite areas near the
narrow tip of the cochlea.
Hearing Loss
Conductive Hearing Loss
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Caused by physical damage to the ear,
reducing the ability of the ear to transfer
vibrations from the outer to the inner ear
May be lessened by hearing aids that
amplify the sound
Sensorineural Hearing Loss
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Caused by damage to the cilia or the
auditory nerve
Increases with age
May be created by prolonged exposure to
loud noise
May be remediated by cochlea implants if
the auditory nerve is intact
Hearing
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Key Takeaways
– Sound waves, vibrating through media such as air, water, or metal, are the stimulus energy
that is sensed by the ear.
– The hearing system is designed to assess frequency (pitch), and amplitude (loudness).
– Sound waves enter the outer ear (the pinna) and are sent to the eardrum via the auditory
canal. The resulting vibrations are relayed by the three ossicles, causing the oval window
covering the cochlea to vibrate. The vibrations are detected by the cilia (hair cells) and
sent via the auditory nerve to the auditory cortex.
Hearing
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Key Takeaways, continued
– There are two theories as to how we perceive pitch: Frequency theory suggests that as a
sound wave’s pitch increases, nerve impulses of a corresponding frequency enter the
auditory nerve. Place theory suggests that we hear different pitches because different
areas of the cochlea respond to higher and lower pitches.
– Conductive hearing loss is caused by physical damage to the ear or eardrum may be
improved by hearing aids or cochlear implants. Sensorineural hearing loss, caused by
damage to the hair cells or auditory nerves in the inner ear, may be produced by prolonged
exposure to sounds over 85db.
Tasting, Smelling, and Touching
Tasting, Smelling, and Touching
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Learning Objectives:
1.
Summarize how the senses of taste and olfaction transduce stimuli into perceptions.
2.
Describe the process of transduction in the senses of touch and proprioception.
3.
Outline the gate control theory of pain. Explain why pain matters and how it may be
controlled.
Tasting
sweet
bitter
sour
Basic
Tastes
piquancy
salty
spicy
unami
savory
Tasting
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2,000 to 10,000 taste buds
– Each bud contains 50-100 receptor cells.
– Some are found on the walls of the mouth and the back of the throat.
Taste buds are activated quickly.
– A sweet or salty taste will trigger a neural impulse within 1/100 second.
Taste buds live for about 5 days.
The rate of taste bud creation slows down as we age.
Smelling
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10 million to 20 million olfactory receptor cells embedded in the olfactory membrane of the
upper nasal passage
– 1,000 types of receptor cells detect 10,000 different odors
Women have a more sensitive sense of smell than do men.
Our sense of smell peaks in early adulthood then declines.
Touching
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pressure
warmth
Basic Touch
Sensations
cold
pain
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Thousands of nerve endings in the skin
respond to four basic sensations.
Other sensations reflect combinations of
these four.
Touching
cold
pressure
wetness
Touching
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Proprioception
– the ability to sense the position and movement of our body parts
– accomplished by specialized neurons in the skin, joints, bones, ears, and tendons
Touching
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Vestibular System
– set of liquid-filled areas in the inner
ear that monitors our head’s position
and movement
– allows us to maintain balance
• semicircular canals – sense
rotational movements
• vestibular sacs – sense linear
accelerations
Experiencing Pain
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Gate Control Theory of Pain
– Pain is determined by two types of nerve fibers in the spinal cord.
• Small fibers carry pain from the body to the brain.
• Larger fibers can open or shut the flow of pain to the brain.
– By massaging a painful area, we activate the larger fibers, shutting off the flow
of pain from the small fibers.
Experiencing Pain
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Both neurochemical and cognitive factors influence the experience of pain.
– endorphins – neurotransmitters that act as the brain’s natural painkillers
– Challenging activities or humor can distract attention from pain.
Tasting, Smelling, and Touching
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Key Takeaways
– The ability to taste, smell, and touch are important because they help us avoid harm from
environmental toxins.
– The many taste buds in our tongue and mouth allow detect six basic taste sensations:
sweet, salty, sour, bitter, piquancy, and umami.
– In olfaction, transduction occurs as airborne chemicals that are inhaled through the
nostrils are detected by receptors in the olfactory membrane. Different chemical
molecules fit into different receptor cells creating different smells.
– On average, women have a better sense of smell than men, and the ability to smell
diminishes with age.
Tasting, Smelling, and Touching
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Key Takeaways, continued
– We have a range of different nerve endings embedded in the skin, combinations of which
respond to four basic sensations of pressure, warmth, cold, and pain. But only the
sensation of pressure has its own specialized receptors.
– Proprioception is our ability to sense the positions and movements of our body parts.
Postural and movement information is detected by special neurons in the skin, joints,
bones, ears and tendons, which pick up messages from the compression and the
contraction of muscles throughout the body.
– The vestibular system in the inner ear, monitors our head’s position and movement and
allows us to maintain balance.
– Gate control theory explains how large and small neurons work together to transmit and
regulate the flow of pain to the brain.
Accuracy and Inaccuracy in Perception
Accuracy and Inaccuracy in Perception
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Learning Objectives:
1.
Describe how sensation and perception work together through sensory interaction,
selective attention, sensory adaptation and perceptual constancy.
2.
Give examples of how our expectations may influence our perception, resulting in
illusions and potentially inaccurate judgments.
How the Perceptual System Interprets the
Environment
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Sensory Interaction
– Different senses work together to
create experience.
• the McGurk effect -- sounds are
misperceived when the auditory
and visual parts of the speech are
mismatched
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Selective Attention
– The ability to focus on some sensory
inputs while tuning out others
• the cocktail party effect –
important stimuli may be
processed even when they are
not the focus of selective
attention
How the Perceptual System Interprets the
Environment
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Sensory Adaptation
– decreased sensitivity to stimuli after
constant and prolonged exposure
– enhances our ability to perceive
important changes in the environment
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Perceptual Constancy
– the ability to perceive stimuli as
unchanging despite changes in
sensation
Illusions
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Illusions occur when the processes that normally help us perceive the world correctly are fooled
by a particular situation so that we see something that is incorrect or nonexistent.
Illusions demonstrate that our perception of the world may be influence by our prior
knowledge.
Illusions do not suggest that perception is generally inaccurate.
Illusions
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The Mueller-Lyer illusion makes the line
segment at the top appear shorter than the
one on the bottom.
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The illusion reflects monocular depth cues–
the bottom line looks like an edge that is
normally farther away from us, while the
top one looks like an edge that is normally
closer.
Illusions
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The Moon Illusion
– The moon always looks larger on the
horizon than when it is high above.
– When you take away the surrounding
distance cues of the horizon, the
illusion disappears.
Illusions
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The Ponzo Illusion
– caused by a failure of the monocular
depth cue of linear perspective
– Both bars are the same size even
though the top one looks larger.
The Important Role of Expectations in Perception
contexts
emotions
expectations
culture
motivations
perception
desires
Accuracy and Inaccuracy in Perception
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Key Takeaways
– Sensory interaction occurs when different senses work together, for instance when taste,
smell and touch together produce the flavor of food.
– Selective attention allows us to focus on some sensory experiences while tuning out
others.
– Sensory adaptation occurs when we become less sensitive to some aspects of our
environment, freeing us to focus on more important changes.
Accuracy and Inaccuracy in Perception
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Key Takeaways, continued
– Perceptual constancy allows us to perceive an object as the same, despite changes in
sensation.
– Cognitive illusions are examples of how our expectations can influence our perceptions.
– Our emotions, motivations, desires, and even our culture can influence our perceptions.
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