Transcript Sensation and Perception

Sensation and Perception
Chapters 5 and 6
Defining Sensation and Perception
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Sensation
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The detection of physical energy from our
environment which we encode as neural signals.
It occurs when energy in the external environment or
the body stimulates receptors in the sense organs.
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“Taking it all in.”
Perception
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The process by which the brain selects, organizes and
interprets our sensory sensations.
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Making sense of what we have taken in.
Separate Sensations
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Sense receptors: Specialized
cells that convert physical
energy in the environment or
the body to electrical energy
that can be transmitted as nerve
impulses to the brain.
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Where are some of your sense
receptor cells?
Sensory Transduction: process
by which our sensory systems
convert stimulus energy into
neural messages.
 That the brain will
understand.
Sensation & Perception Processes
Bottom-up Processing
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Sensory analysis
that starts at the
entry level.
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Begins with the
sensory receptors
Moves up to the
brain.
Top-down Processing
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How our minds
interpret what our
senses detect.
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The experiences
and expectations
we use to interpret
information.
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The Forest Has Eyes
The Forest has Eyes
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Bottom-up: Our sensory
systems detect the lines,
angles and colors that form
the horses, rider and
surroundings.
Top-down: We consider the
title, notice the apprehensive
expressions, then direct our
attention to the parts of the
painting that give those
observations meaning.
Ambiguous Figure
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What do you sense?
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Bottom-up
What do you
perceive?
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Top-down
What did she say?
“Mares eat oats and
does eat oats.
And little lambs eat
ivy.
A kid’ll eat ivy, too.
Wouldn’t you?”
Absolute Threshold
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The smallest quantity of
physical energy that can
be reliably detected by
an observer.
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The stimulation needed
for us to detect the
stimulus 50% of the
time.
We are more sensitive
to some things than
others.
Absolute Sensory Thresholds
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Vision:
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Hearing:
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1 drop of perfume in a 6-room apartment
Touch:
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The tick of a watch from 20 feet in total quiet
Smell:
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A single candle flame from 30 miles on a dark, clear
night
The wing of a bee on your cheek, dropped from 1 cm
Taste:
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1 tsp. Sugar in 2 gal. water
Signal Detection Theory
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Predicts how and when we
will detect a faint stimulus
(signal) amid background
stimulation (noise).
Assumes detection depends
partly on a person’s
experiences, motivation, and
level of fatigue.
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Absolute thresholds vary.
Seeks to understand why.
QuickTime™ and a
TIFF (Uncompressed) decompressor
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Subliminal Stimuli
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Stimuli that is below
our absolute
threshold.
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We can process
information without
being aware of it.
May have a subtle,
fleeting effect on
thinking.
The Pepsi Cool Can
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In 1990, Pepsi withdrew one of its
“Cool Can” designs after
someone protested that Pepsi was
subliminally manipulating people
by designing the cans such that
when six packs were stacked at
grocery stores, the word SEX
would emerge from the seemingly
random design.
Critics alleged that the red and
blue lines on the “Cool Can”
design were far from random.
Backmasking
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Backmasking site
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Listen to the song.
Can you tell what it
says?
What type of
processing is this?
Signal Detection Theory
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Tries to understand why
people respond
differently to different
stimuli.
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Absolute thresholds
vary.
Our psychological and
physical states
influences our ability to
detect stimulus.
Difference Threshold
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The smallest difference in
stimulation that can be
reliably detected by an
observer when two stimuli are
compared;
Also called Just Noticeable
Difference (JND).
It increases with the
magnitude of the stimulus.
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Weber’s Law: The size of the
JND is proportional to the
intensity of the stimulus.
Sensory Adaptation
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The reduction or disappearance
of sensory responsiveness when
stimulation is unchanging or
repetitious.
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After constant exposure to
stimulus our nerve cells fire less
frequently.
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Jumping in a swimming pool
Habituation
Prevents us from having to
continuously respond to
unimportant information.
Sensory Overload
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Over-stimulation of the senses.
Can use selective attention to reduce
sensory overload.
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Selective attention
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The focusing of attention on selected aspects of
the environment and the blocking out of others.
Vision: What We See
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What strikes our eyes is not color but pulses of
electromagnetic energy that our visual system
experiences as color.
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Different species see different portions of the
spectrum.
Waves
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Wavelength: The distance from one peak to the next.
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Determines the color we experience or hue.
Short wavelengths also mean higher pitched sounds.
Waves
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Intensity: The height of the light waves.
Determines the brightness.
Great amplitude
Short wavelength=high frequency
(bluish colors, high-pitched sounds) (bright colors, loud sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Small amplitude
(dull colors, soft sounds)
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Cornea
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Lens
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Focuses on objects by
changing shape.
Iris
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Protects eye and bends
light toward lens.
Controls amount of light
that gets into eye.
Pupil
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Widens or dilates to let
in more light.
An Eye on the World
An Eye on the World
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Retina
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Rods
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Neural tissue lining the back of the eyeball’s interior, which
contains the receptors for vision.
Made from a piece of brain as fetus
Visual receptors that respond to dim light.
Share bipolar cells with many other rods.
Cones
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Visual receptors involved in color vision. Most humans have 3
types of cones.
Help detect fine details
Located in fovea
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Have a “hotline to the brain” with own bipolar cells.
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The Structures of the Retina
The Optic Nerve
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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.
Receptors in the Human Eye
Cones
Rods
Number
6 million
120 million
Location in
retina
Center
Periphery
Sensitivity in
dim light
Low
High
Color sensitive?
Yes
No
Visual Information Processing
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Feature Detectors
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Cell’s
responses
Stimulus
Nerve cells in the
brain that respond to
specific features of
the stimulus
shape
 angle
 movement
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Parallel Processing
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Parallel Processing
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processing several aspects
of a problem
simultaneously
The retina projects to
several areas of the visual
cortex at the same time.
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Blindsight
the brain’s natural mode of
information processing for
many functions, including
vision
Trichromatic Theory
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Young (1802) & von
Helmholtz (1852) both
proposed that the eye detects
3 primary colors:
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Red, blue, & green
Three different types of
cones, one for each color.
All other colors can be
derived by combining these
three.
Opponent-Process Theory
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A competing theory of
color vision, which
assumes that the visual
system treats pairs of
colors as opposing or
antagonistic.
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If you see one color on one
point of the retina you can’t
see the other at the same
time.
Red and green
Blue and yellow
Black and white