Transcript Sensation and Perception

Sensation and Perception
• Sensation
– The process of sensing our environment through
touch, taste, sight, sound, and smell.
– This information is sent to our brains in raw form
where perception comes into play.
• Perception is the way we interpret these
sensations and therefore make sense of
everything around us.
Sensory Receptors
• Specialized cells unique to each sense organ
that respond to a particular form of sensory
stimulation
• Eye (Sense organ of vision)
– Rods and cones (transducers) respond to light
wave energy and convert this energy into
electrical impulses.
Absolute Threshold
• The absolute threshold is the point where something
becomes noticeable to our senses 50% of the time.
• It is the softest sound we can hear or the slightest touch
we can feel. Anything less than this goes unnoticed.
• The absolute threshold is therefore the point at which a
stimuli goes from undetectable to detectable to our
senses.
Absolute Thresholds
Sense
Absolute Threshold
Vision
Candle flame thirty miles away on a clear,
dark night
Hearing
The tick of a watch at twenty feet
Smell
One drop of perfume throughout a threeroom apartment
One teaspoon of sugar in two gallons of
water
A bee’s wing falling on your cheek from a
height of about half an inch
Taste
Touch
Difference Threshold
• The difference threshold is the amount of
change needed for us to recognize that a
change has occurred 50% of the time.
• This change is referred to as the Just
Noticeable Difference.
• Weber’s Law
– Change must be proportional larger or smaller to detect
a change.
• Weight must be a minimum 2% different for most people to
notice a difference
Signal Detection Theory
• We are often faced with the daunting task of
focusing our attention on certain things while
at the same time attempting to ignore the
flood of information entering our senses.
• When we do this, we are making a
determination as to what is important to
sense and what is background noise.
• This concept is referred to as signal
detection because we attempt to detect what
we want to focus on and ignore or minimize
everything else.
Sensory Adaptation
• Stimuli which has become redundant or
remains unchanged for an extended period
of time.
• Once we adapt to the perfume or the ticking
of the clock, we stop recognizing it.
• This process of becoming less sensitive to
unchanging stimulus is referred to as
sensory adaptation
• If it doesn't change, why do we need to
constantly sense it?
Light
• Electromagnetic energy
• ROY G. BIV
Short wavelengths
Long wavelengths
Parts of the Eye
• Cornea
– Transparent tissue covering the front of the eye. Does not have any blood
vessels; does have nerves. Focus light into the pupil
• Lens
– Transparent tissue that bends light passing through the eye. To focus light, the
lens can change shape by bending and flips the light onto the retina.
• Pupil
– Hole in the center of the eye where light passes through.
• Iris
– Circular band of muscles that controls the size of the pupil. It controls the
amount of light that enters the eye. The pigmentation of the iris gives "color" to
the eye. Blue eyes have the least amount of pigment; brown eyes have the most.
• Aqueous Humor
– Clear, watery fluid found in the anterior chamber of the eye.
Parts of the Eye
• Retina
– Layer of tissue on the back portion of the eye
that contains cells responsive to light
(photoreceptors)
• Fovea
– Greatest visual acuity with most cones
• Rods
– Photoreceptors responsive in low light
conditions. Rods are found on the edges of the
retina
– There are 20x more rods than cones –60 million
• Cones
– Photoreceptors responsive to color and in bright
conditions. 3 million cones split between red,
blue and green. Cones are found mostly in the
fovea which causes best visual acuity
Parts of the Eye
• Sclera
– Protect coating around the
posterior five-sixths of the
eyeball
• Vitreous Humor
– Clear, jelly-like fluid found
in the back portion of the
eye. Maintains shape of the
eye.
• Blind Spot
– Spot where the ganglion
cells combine to form the
optic nerve (there are no
receptors here)
• Optic Chiasm
– crossover point to the
occipital lobe
Light and Dark Adaptation
• Light
– Cones and rods both
adapt quickly (within one
minute)
– Rhodopsin (pigment)
bleaches (breaks down)
quickly so the rods and
cones are less sensitive
• Dark
– Cones respond quickly
(within ten minutes)to less
light.
– Rods are more sensitive to
light but slower to respond
– Rods take thirty minutes to
reestablish rhodopsin in
them and reach their greatest
level of sensitivity
– Dusk is very difficult on the
eyes
• Perceptual experience of different wavelengths of
light
• White light contains all colors
– Hue
• property of wavelength known as color
– Saturation
• Purity of the light wave, richness produced a single wavelength
– vivid color vs faded or washed out
– Brightness
• Intensity of a color based on the amplitude of the wavelength
• Subtractive
• Additive
– White light contains all colors
– Light mixing has three primary hues
• Red, blue and green
• Mix these wavelengths together to
make different colors
• All wavelengths mixed together
produce white
– Paint absorbs all light except the
color it is
– The three primary colors of paint
are
• Red, blue and yellow
• Mix all colors together
produces black
Color Theory
• Trichromatic Theory
– Formed by John Young and
Herman Helmholtz
– Three cones red, blue, green
have different light sensitive
chemicals called opsin that are
stimulated by light waves and
combine to give us the colors
– This theory explains color vision
in the eye
• Opponent Process
– Formed by Ewald Hering
– Three pairs of cells
– Red-Green, blue-yellow, and blackwhite
– You cannot see a red-green color or a
blue yellow color because when one
side is stimulated the other is inhibited
– Cells are in the ganglion cells and the
thalamus
– Explains afterimages
Afterimages
The cell rests after continuously firing which causes the opposite cell to fire
Complementary colors
Do you see
the colors in
the opposite
position?
Combined color Theory
Color-Blindness
•
•
•
•
•
On the X gene
8% of men and 1% of women
Most people are red-green color-blind
Blue-yellow color-blindedness is more rare than no color
Ishihara Test
Last thoughts on Color
• What color do you see best in the day?
– Green-yellow
• What light color do you see best at night?
– Blue
• What light color does your eyes not become
light adapted to?
– Red – dark rooms and submarines
Normal vision = 20/20
Nearsighted = Eyeball is too long and light is focused at a point in front
of the retina causing the inability to see distant objects clearly
Farsighted = Eyeball is too short and light is focused at a point slightly
behind the retina causing near objects to seem fuzzy
Parts of the Ear
• Outer Ear
The most apparent
structure of hearing is the
external ear or pinna, a
structure that partially
blocks sounds from the rear
of the head.
– Its function of directing
sounds toward the inner
structures.
– Sound enters the ear canal or
meatus and vibrates the ear
drum or tympanum.
Middle Ear
• The vibrations of the ear drum are
transmitted to a set of three bones or
ossicles which transmit the sound energy
to the oval window of the cochlea.
– Malleus- Hammer
– Incus- Anvil
– Stapes- Stirrup
• The cochlea contains the receptor end
organs which generate the neural
impulses corresponding to sound.
• The middle ear is connected to the throat
by the eustacian tube and this structure
allows regulation of pressure on the ear
drum and the oval window of the cochlea.
Inner Ear
• Both the cochlea (hearing) and the semicircular canals or
nonauditory labyrinth (balance) are contained in the inner
ear.
• The sense of balance and hearing share the eighth cranial
nerve there is some interaction between them.
• The cochlea is a coiled structure making about two and onehalf turns.
• The upper and lower gallery of the cochlea are divided by
the basalar membrane.
• Lying on the basalar membrane in the upper gallery is the
organ of corti from which hair cells (the actual receptors
for hearing) project and move in response to vibrations of
the basalar membrane.
•
Cilia Hair Cells
• Hair cells closest to the oval window respond most
strongly to high frequency sound while those
furthest from the oval window respond most
strongly to low frequency sound.
• The upper frequency threshold is about 20,000 Hz.
while the lower threshold is about 25 Hz. The
upper threshold varies with age, decreasing to
around 10,000 Hz. at age fifty.
Sound
• Frequency (measured in cycles per second or cps,
now called Hertz or Hz)
– frequency yields pitch (a high or low tone)
– low frequency limit of 22 Hz and a high frequency
limit of 22,000 Hz, corresponds to the functional limits
of the human ear.
–
• Amplitude (measured in decibels or dB, named
after Alexander Graham Bell)
– amplitude yields loudness (a loud or soft sound)
Loudness
decib
els
-30
-20
-10
0
microwatts (per
cm. sq.)
1/1000
1/100
1/10
1
+10
+20
+30
10
100
1000
+50
100000
Intensity
Sound
(db)
Ticking of a Watch 20
Whisper
Normal Speech
Car Traffic
Alarm Clock
30
50-60
70
80
Lawn Mower
Chain Saw
Jackhammer
95
110
120
Jet Engine
130
Place Theory
• "Place theory" - receptors at different places
are sensitive to different frequencies
• High frequency tones seem to create standing
waves close to the oval window
• Low frequency tones seem to create standing
waves far from the oval window
• Intermediate frequency tones seem to create
standing waves at intermediate distances
Frequency Theory
• "Frequency theory" - auditiory nerve impulses
reproduce the sound wave pattern
• Neither notion about determination of pitch fully
accounts for the known facts.
• Place theory does not tell us how the wave form of
the sound is reproduced in the auditory nerve,
however, for frequences above 1000 Hz nerve
impulses cannot follow the wave form.
Volley Theory
• Combines cells together firing in sequence
• Only explains up to 4000 Hz.
Ear Damage
1. Tinnitus is perceived as a "ringing in the ears" and
usually sounds like a high pitched tone. It may have
its origin in extreme stimulation (above 130 db)
2. As people age their hearing degrades in the higher
frequency ranges.
3. Prolonged exposure to loud sounds affects 10002000 Hz range and the damage is not reversable as
the receptors damaged do not regenerate.
• Every time we inhale,
currents of air swirl up
through the nostrils,
over a “sheet” about
the size of a small
postage stamp that
contains millions of
olfactory receptor
neurons. This is the
olfactory epithelium.
• Humans are able to
distinguish over
10,000 different odor
molecules.
• Smell is the sense that
travels directly to the
brain which is actually
exposed to the
atmosphere
Sense of Smell
Pheromones
• Chemical smells that attract opposite sex
Taste
• For food to have a taste, it must be dissolved in water.
• There are four basic tastes: sweet, salty, sour and
bitter:
SWEET
Like a piece of
cake
SOUR
SALTY
BITTER
Like a lemon
Like, well,
salt!
Like a cup of bad
coffee
• The sour taste- This is the taste of acids. The more acidic the substance the
more sour the taste. Acids include hydrogen ions in their chemical makeup. The
intensity of the sour taste is approximately proportional to the logarithm of the
hydrogen ion concentration.
• The salty taste- Ionized salts are responsible for eliciting this taste perception.
Different salts have slightly different tastes because they also contain other
basic taste components.
• The sweet taste- There is a long list of substances that yield the sweet taste. You
will be familiar with sugars (e.g., sucrose, fructose, glucose, maltose, lactose)
but glycols, alcohols, and aldehydes are also included. Nearly all are organic
compounds. Sucrose is considered a basic comparison substance and is given a
sweetness index of 1. Saccharin, by contrast, has an index of over 600.
• The bitter taste- Like the sweet taste there is a long list of substances that elicit
the bitter taste. Most are also organic. One significant group of organic
substances which tastes bitter is the alkaloids. This may have survival value
since many of the deadly toxins in poisonous plants are alkaloids and intense
bitter tastes are normally rejected.
Kinesthetic
• The sense of muscular movement and
bodily positioning is something of which
we are little aware.
• Put your right hand behind your head. How
do you know where it is?
• Located in the joints and ligaments in
throughout the body
Vestibular
• The vestibular sense is the sense of balance.
• The vestibular system is located in the
semicircular canals in the ears.
• Ear infections can lead to dizziness and
balance issues
• Vision also plays a role in your sense of
balance.
Figure-Ground
• Grouping some
sensations into an object,
or figure that stands out
on a plainer background
• Camouflage is used to
breakup figure-ground
Reversible Figures
• It is when two
objects can
either be in the
foreground or
the background
Gestalt Principles
• The German word "Gestalt" roughly translates to
"whole" or "form," and the Gestalt psychologist's
sincerely believed that the whole is greater than the
sum of its parts.
• In order to interpret what we receive through our
senses, they theorized that we attempt to organize this
information into certain groups.
• The Gestalt principles of grouping include four types:
similarity, proximity, continuity, and closure.
Similarity
• Our tendency to group things together based upon
how similar to each other they are. In the first figure
above, we tend to see two rows of red dots and two
rows of black dots. The dots are grouped according to
similar color.
Proximity
• We tend to perceive three columns of two lines
each rather than six different lines. The lines
are grouped together because of how close
they are to each other, or their proximity to one
another.
Continuity
• Our tendency to see patterns and
therefore perceive things as belonging
together if they form some type of
continuous pattern.
Closure
• Finally, in the fourth figure, we
demonstrate closure, or our tendency to
complete familiar objects that have gaps
in them.
• Even at first glance, we perceive a circle
and a square.
Perceptual Constancy
• Our ability to see things differently
without having to reinterpret the object's
properties. There are typically three
constancies discussed, including size,
shape, brightness.
Size Constancy
• Our ability to see objects as
maintaining the same size even
when our distance from them
makes things appear larger or
smaller.
• This holds true for all of our
senses.
• As we walk away from our radio,
the song appears to get softer.
• We understand, and perceive it
as being just as loud as before.
• The difference being our
distance from what we are
sensing.
Shape Constancy
• The perceived
shape of an object
is unaffected by
changes in the
shape of its retinal
image.
Brightness Constancy
• Our ability to recognize that color
remains the same regardless of how it
looks under different levels of light.
• Without color constancy, we would be
constantly re-interpreting color and
would be amazed at the miraculous
conversion our clothes undertake.
Color Constancy
Perceiving Distance
• Monocular Cues
– those cues which
can be seen using
only one eye.
– They include size;
linear perspective
texture, overlap,
shading, height, and
clarity
• Binocular Cues
– those depth cues in
which both eyes are
needed to perceive.
– There are two
important binocular
cues; convergence
and retinal disparity.
How we measured early depth
perception
• Visual Cliff
Linear Perspective
• Apparent convergence of parallel lines.
Convergence implies greater distance
Texture Gradient
• Objects tend to become
smoother as the object gets
farther away, suggesting that
more detailed textured objects
are closer.
Overlap-Interposition-Superposition-Occlusion
• those objects
covering part of
another object is
perceived as
closer.
Shadowing-Shading
• Shadows of objects can give a clue to their
distance, allowing closer objects to cast
longer shadows which will overlap objects
which are farther away.
Height in Field-Elevation
• Objects which are closer
to the bottom of our
visual field are seen as
closer to us due to our
perception of the horizon,
where higher (height)
means farther away.
Clarity-Aerial-Atmospheric Perspective
• Similar to texture, objects tend to get blurry as
they get farther away, therefore, clearer or more
crisp images tend to be perceived as closer.
Binocular Cues
•
•
•
•
Takes two eyes
Convergence
Retinal Disparity
Stereoscopic vision
Convergence
• The fact that the closer an object, the more inward our
eyes need to turn in order to focus. The farther our
eyes converge, the closer an object appears to be.
Convergence vs. Accommodation
• Convergence- Eyes move toward or away from each other
• Accommodation- Lens moves to bring the vision into focus
– Good up to 20 feet
Retinal Disparity
• The 2.4 inch (6 cm) distance between the two pupils causes us to
see two slightly different images of the world. This displacement
between the horizontal positions of corresponding images is called
binocular disparity.
• Our eyes see two images which are then sent to our brains for
interpretation, the distance between these two images, or their
retinal disparity, provides another cue regarding the distance of
the object. Gives us stereoscopic vision
Motion Parallax
• When moving, the relative distances of objects
determine the amount and the direction of their
relative movement in the retina image.
• If you now move your head to one side, the images
closer to you will move more, while objects farther
will remain still.
Relative Motion
Impossible Figures
• It is not the drawing itself that is impossible, but only your threedimensional interpretation of it.
•Given the chance to interpret a drawing or image as threedimensional, your visual system will do so.
•It does not generally take a perspective drawing and reinterpret
it as flat, because there is a spatial paradox.
M.C. Escher
Muller-Lyer
Necker Cube
Ames Room