Sensation and Perception
Our Sensational Senses





What is the difference between
sensation and perception?
What is psychophysics?
How do we measure the senses?
What is sensory adaptation?
When do you experience sensory
overload?
Defining Sensation and
Perception

Sensation




The detection of physical energy emitted or
reflected by physical objects.
It occurs when energy in the external
environment or the body stimulates
receptors in the sense organs.
The study of sensation is the study of
energy.
Perception

The process by which the brain organizes
and interprets sensory information.
Ambiguous Figure

Colored surface can
be either the outside
front surface or the
inside back surface


Cannot
simultaneously be
both
Brain can interpret
the ambiguous cues
two different ways
Separate Sensations

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.
Transduction: the process
where physical energy is
converted to
electrochemical.
Sensation & Perception
Processes
Why do have different senses?


Different sensorys exist because signals
received by the sense organs stimulate
different nerve pathways leading to
different areas of the brain.
Synthesia


A condition in which stimulation of one
sense also evokes another.
Red Mondays…video clip?
What is Psychophysics?


Discipline within psychology that
quantitatively investigates the relationship
between physical stimulus and the sensations
and perceptions they affect.
1860-Gustav Fechner is founding father

Do you remember what Wilhelm Wundt did?

He built on Fechner’s work and started his own
psychological research lab!
We can measure senses by…



Absolute threshold
Difference threshold
Signal-detection theory
Absolute Threshold

The smallest quantity of physical energy that
can be reliably detected by an observer (50%
of the time in general population)
Absolute Sensory Thresholds

Vision:


Hearing:


1 drop of perfume in a 6-room apartment
Touch:


The tick of a watch from 20 feet in total quiet
Smell:


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:

1 tsp. Sugar in 2 gal. water
Difference Threshold



The smallest difference in stimulation that
can be reliably detected by an observer when
two stimuli are compared;
Also called Just Noticeable Difference (JND).
Weber’s Law: JND is proportional to stimulus
intensity

Greater the magnitutude of the stimulus, the
larger the difference must be to be noticed
Signal-Detection Theory


A psychophysical theory that divides the detection of a
sensory signal into a sensory process and a decision
process.
Bias plays a role in detecting stimulus. It can be
psychological or physical. (mom and her new baby)
 Four Possible Outcomes on each trial in detection of
stimulus




Hit: signal present participant sensed it
Miss: Signal present but participant did not sense it
False Alarm: Signal absent but participant reported sensing it
Correct Rejection: Signal absent and participant did not report
it
Sensory Adaptation and
Deprivation

Adaptation (Habituation)



The reduction or disappearance of sensory
responsiveness when stimulation is unchanging
or repetitious.
Prevents us from having to continuously
respond to unimportant information (our
clothes).
Deprivation

The absence of normal levels of sensory
stimulation.
Sensory Overload


Overstimulation of the senses.
Can use selective attention to reduce
sensory overload.

Selective attention

The focusing of attention on selected aspects
of the environment and the blocking out of
others.
Go to Perception
Vision:





What do we see?
Eye, see? What makes up the eye?
Why is the visual system is not a camera?
How do we see colors?
How do we construct the visual world?
Vision


Most important sense (evolution)
Photoreceptors gather light, send it to
neuron, occipital lobe for decoding
What We See

Hue


Brightness


Visual experience specified by color names
and related to the wavelength of light.
Lightness and luminance; the visual
experience related to the amount of light
emitted from or reflected by an object.
Saturation

Vividness or purity of color; the visual
experience related to the complexity of
light waves.
What We See



Hue
Brightness
Saturation

Cornea



Focuses on objects by
changing shape.
Iris


Protects eye and
bends light toward
lens.
Lens

Controls amount of
light that gets into
eye.
Pupil

An Eye on the World
Widens or dilates to
let in more light.
An Eye on the World

Retina



This is where transduction takes place (rods and cones)
Rods



Neural tissue lining the back of the eyeball’s interior, which
contains the receptors for vision.
Visual receptors that respond to dim light.
Light and dark but no color.
Cones



Visual receptors involved in color vision. Most humans have 3
types of cones.
Best in bright light, can sharply focus
5 million different shades but we only have 150 in our
language
Blind Spot
Blind Spot


At the point where the optic nerve exits
the back of the eye there are no rods
and cones so no receptors for vision
Head and eye movements work avoid
“blind spots” in our vision
The Structures of the Retina
Why is the Visual System not a
Camera?

Much visual processing is done in the
brain.



Some cortical cells respond to lines in specific
orientations (e.g. horizontal).
Other cells in the cortex respond to other
shapes (e.g., bulls-eyes, spirals, faces).
Feature-detectors

Cells in the visual cortex that are sensitive to
specific features of the environment.
Hubel & Wiesel’s Experiment
How We See Colors


Trichromatic theory
Opponent process theory
Trichromatic Theory

Young (1802) & von
Helmholtz (1852) both
proposed that the eye
detects 3 primary
colors:


red, blue, & green
All other colors can be
derived by combining
these three.
Opponent-Process Theory


A competing theory of color vision, which
assumes that the visual system treats pairs of
colors as opposing or antagonistic
States there are two types of cones


One responds to red and green, the other to blue
and yellow, while the rods receive black and white
input
As one color in each pair is excited, the other is
inhibited
Afterimages
Stare at the white, what do
you see?
Stare at the light bulb for 30
seconds….
Why does this happen?




When you focus on the black light bulb, light
sensitive photoreceptors in your retina respond to
incoming light. The longer you stare at the black light
bulb, your photorecpeptors become desentitized or
fatigued.
Photopigment is “bleached” by constant stimulation.
The desensitization is strongest for cells viewing the
brightest area and weaker for darker images.
When screen becomes white, the least depleted cells
respond more strongly producing the brightest part
of the after image: the glowing light bulb.
This is a negative after image. (dark areas turn light)
Test of Color Deficiency
Hearing



Do you hear what I hear?
How does the ear hear?
How do we construct the auditory
world?
Hearing



Sounds created by vibrations push air
molecules back and forth changing air
pressure.
Changes in air pressure=sine wave
Frequency Theory:


Fast waves=frequency (high or low)
High waves=amplitude (loud or soft)
What We Hear

Loudness


Pitch



The dimension of auditory experience related to the
intensity of a pressure wave.
The dimension of auditory experience related to the
frequency of a pressure wave.
Place Theory: Suggests we identify pitch of sounds
according to the location of vibrations on the basilar
membrane
Timbre (pronounced “TAM-bur”)

The distinguishing quality of sound; the dimension of
auditory experience related to the complexity of the
pressure wave.
Listen to the Hearing Test


Ultimate Hearing Test

When do you stop hearing the sound?

http://www.youtube.com/watch?v=igGroIcga3g
Hertz:

Unit of measure for the frequency of sound
An Ear on the World
Auditory Localization

Sounds from different
directions are not identical
as they arrive at left and
right ears





Loudness
Timing
Phase
The brain calculates a
sound’s location by using
these differences.
Virtual Barber Shop:
http://www.youtube.com/w
atch?v=IUDTlvagjJA
Hearing is possible…




When ear and brain convert sine waves
from sound
Sound travels into ear, bone in the
middle ear transfers into inner ear
where the sound makes fluid waves
Vibration of fluid waves stimulate tiny
hairs to generate nerve impulse
Brain then analyzes sound.
Other Senses





Taste: savory sensations
Smell: The sense of scents
Senses of the skin
The mystery of pain
The environment within
Taste: Savory Sensations


Transduction: chemical molecules and
saliva dissolve
Papillae


Knoblike elevations on the tongue, containing
the taste buds (Singular: papilla).
Taste buds

Nests of taste-receptor cells.
Taste Buds


Photograph of tongue
surface (top), magnified
75 times.
10,000 taste buds line
the tongue and mouth.


Taste receptors are down
inside the “bud”
Children have more
taste buds than adults.
Four Tastes

Four basic tastes


Salty, sour, bitter and sweet.
Different people have different tastes
based on:




Genetics
Culture
Learning
Food attractiveness
Smell: The Sense of Scents



Very primitive! But very useful. Close connection to memory
Airborne chemical molecules enter the nose and circulate through the
nasal cavity.
 Vapors can also enter through the mouth and pass into
nasal
cavity.
Receptors on the roof of the nasal cavity detect these molecules.
Olfactory System
Sensitivity to Touch
Gate-Control Theory of Pain

Experience of pain
depends (in part) on
whether the pain
impulse gets past
neurological “gate” in
the spinal cord and
thus reaches the
brain.
Neuromatrix Theory of Pain

Theory that the
matrix of neurons in
the brain is capable
of generating pain
(and other
sensations) in the
absence of signals
from sensory
nerves.
The Environment Within

Kinesthesis


Equilibrium


The sense of body position and movement of body
parts; also called kinesthesia.
The sense of balance.
Semicircular Canals

Sense organs in the inner ear, which contribute to
equilibrium by responding to rotation of the head.
What do you see?
Perception

To what extent are our perceptions of
the environment accurate?



Perception is the process of selecting
information from the environment and
interpreting that information.
Perception brings meaning to sensation.
It produces an intrepretation of the world
not a perfect representation!
Stare at the image for 30
seconds….
Which line is longer?
What picture looks like a
whole room?
Feature Detectors



Still a mystery to most psychologist.
These are a bundle of cells in the brain
whose purpose is to detect certain
features of stimuli (such as lines,
shapes, angles, movements)
Discovered by David Hubel and Torsten
Wiesel.
How do we perceive the
world?

Attention- a process in which consciousness is
focused on particular stimuli



Selective Attention – ability to focus on one
stimulus while excluding other stimuli that are
present
Divided Attention – ability to respond to more than
one stimulus
Cocktail Party Effect: demonstrates that attention
can be divided but you can hear things that are
important to you (like hearing your name in a
busy room)
What do you pay attention to?

The Amazing Color Changing Card Trick

http://www.youtube.com/watch?v=voAntzB7EwE

Awareness Test
http://www.youtube.com/watch?v=Ahg6qcgoay4
How do we process stimuli?

The ability to discriminate among shapes and
figures.

Bottom-up processing – information processing
that beings at the stimulus and continues to
higher brain centers

Top-down processing – information processing
that begins in higher brain centers (what we
already know) and proceeds to receptors of
stimulus
Is this Top Down or Bottom
Up?

The Count Censored –


http://www.youtube.com/watch?v=B-Wd-Q3F8KM
Top Down Processing Example


Video: Sensation and Perception
Ted TV: click here
How do we construct the visual
World?




Form perception
Depth and distance perception
Visual constancies: When seeing is
believing
Visual illusions: When seeing is
misleading
Form Perception


Gestalt principles describe the brain’s organization of
sensory information into meaningful units and
patterns.
Refers to recognition and identification of faces,
words, shapes, melodies, etc.
 Feature-analysis theory – theory of pattern
perception stating that we perceive basic elements
of a structure and then mentally create a complete
picture
 Pragnanz Theory: We see the simpliest pattern
possible.
 Prototypes-matching theory – patterns are
identified by being compared against a set of
prototypical patterns stored in memory
Form Perception (cont.)

Figure-ground perception – tendency to organize that visual field

Closure – Filling in missing information from the perceptual array

Laws of Grouping
into objects (figures) that stand apart from surroundings
(ground)
by closing in gaps


Similarity – grouping things on the basis of how similar they
are to one another
Proximity – grouping things on the basis of how near they are
to one another
Figure and Ground
MC Esher Relativity
Waterfall
Tree
Depth and Distance
Perception

Binocular Cues:



Visual cues to depth or distance that
require the use of both eyes.
Convergence: Turning inward of the eyes,
which occurs when they focus on a nearby
object.
Retinal Disparity: The slight difference in
lateral separation between two objects as
seen by the left eye and the right eye.
Depth and Distance
Perception

Monocular Cues:

Accommodation





Bulging and elongating of lens
Effective only for objects within 25 feet
Motion parallax – phenomenon where near objects are
seen as moving more rapidly that far objects when the
viewer’s head is moving
Texture gradient – texture of a surface receding in the
distance changes in clarity, blurring at further distances
Linear perspective – produced by apparent converging of
parallel lines in the distance
The Ames Room



A specially-built room
that makes people
seem to change size as
they move around in it
The room is not a
rectangle, as viewers
assume it is
A single peephole
prevents using
binocular depth cues
Research suggests that the visual system is upset by redundancy of
patterns (when there is nothing apparently there).
Visual Constancies

The accurate perception of objects as
stable or unchanged despite changes in
the sensory patterns they produce.





Shape constancy
Location constancy
Size constancy
Brightness constancy
Color constancy
Shape Constancy

Even though these images cast shadows of
different shapes, we still see the quarter as
round
Which line is longer?
Visual Illusions

Illusions are valuable in understanding perception
because they are systematic errors.


Illusions provide hints about perceptual strategies.
In the Muller-Lyer illusion (above) we tend to perceive
the line on the right as slightly longer than the one on
the left.
The Ponzo Illusion



Linear perspective
provides context
Side lines seem to
converge
Top line seems
farther away

But the retinal
images of the red
lines are equal!
Fooling the Eye



The cats in (a) are the same size
The diagonal lines in (b) are parallel
You can create a “floating fingertip frankfurter” by
holding hands as shown, 5-10” in front of face.
Perceptual Powers: Origins and
Influences


Depth perception appears around 6 months of age
Psychological and cultural influences on perception



Two competing theories:



We use prior experience and learning when we interpret
sensory information
City dwellers vs. country dwellers will experience the Ponzo
Effect differently when around large buildings
Learning Theory: Learned depth cues
Innate Theory: Born with certain depth cues
Bottom Line: Perception is an interaction of nature
vs. nurture
The Visual Cliff-40 Studies



Glass surface, with checkerboard
underneath at different heights
 Visual illusion of a cliff
 Baby can’t fall
Mom stands across the gap
Babies show increased attention
over deep side at age 2 months, but
aren’t afraid until about the age
they can crawl (Gibson & Walk,
1960)
The Visual Cliff
Psychological and Cultural
Influences on Perception




We are more likely to perceive something when we
need it.
What we believe can affect what we perceive.
Emotions, such as fear, can influence perceptions of
sensory information.
Expectations based on our previous experiences
influence how we perceive the world.

Perceptual Set


A habitual way of perceiving, based on expectations.
All are influenced by our culture.
Perceptual Set

What you see in the centre figures depends
on the order in which you look at the figures:


If you scan from the left, see an old woman
If you scan from the right, see a woman’s figure
Context Effects




Word Game
The same physical
stimulus can be
interpreted differently
We use other cues in
the situation to resolve
ambiguities
Is this the letter B or
the number 13?
Subliminal Perception

Perceiving without awareness



visual stimuli can affect your behavior even
when you are unaware that you saw it
nonconscious processing also occurs in
memory, thinking, and decision making
these effects are often small, however, and
difficult to demonstrate and work best with
simple stimuli
Subliminal Perception

Perception versus Persuasion


there is no empirical research to support
popular notions that subliminal persuasion
has any effect on a person’s behavior
persuasion works best when messages, in
the form of advertising or self-help tapes,
are presented above-threshold, or at a
supraliminal level
Extrasensory Perception

Extrasensory Perception (ESP):



The ability to perceive something without
ordinary sensory information
This has not been scientifically
demonstrated
Three types of ESP:



Telepathy – Mind-to-mind communication
Clairvoyance – Perception of remote events
Precognition – Ability to see future events
Parapsychology



The study of purported psychic
phenomena such as ESP and mental
telepathy.
Persinger suggests that psychic
phenomena are related to signs of
temporal lobe epilepsy in otherwise
neurologically normal individuals.
Most ESP studies produce negative
findings and are not easily replicated.
Parapsychology


J. B. Rhine conducted many experiments on
ESP using stimuli such as these.
Rhine believed that his evidence supported
the existence of ESP, but his findings were
flawed.
Quiz over Perception





What is selective attention?
According to feature analysis theory, how do
we identify objects that we percieve?
What is the figure ground relationship?
Which Gestalt principle helps our perception
of WWWW XXX?
Your mother claims she was able to read your
mind and knew you would try to sneak some
food before dinner. What form of ESP might
she claim?