Bell Work
• What is the difference between
sensation and perception?
Objective
• Students will differentiate between
S&P.
What do you see?
What Do you Know?
Reality is merely an illusion, although
a very persistent one.
Albert Einstein
kids.niehs.nih.gov/illusion/illusions.htm
What is the difference between
Sensation and Perception?
Sensation furnishes the raw material of sensory experience,
while perception provides the finished product
Sensation is the sensory process that
detects visual, auditory, and other sensory stimuli
and transmits them to the brain.
Perception is the brain process that:
• actively organizes sensory
information
• and interprets sensory information
Perception: The Basic Process
• Physical presence of something
• Sensory detection of it
• (eyes, ears, nose, tongue, skin)
• Transduction of physical energy to a signal that the
brain can use (neurotransmission)
• Analysis of attributes (size, edges)
• Comparison of object to known objects in memory
• Attention (or not)
• Recognition of object and its location
• Action
• Memory
Bottom-up Processing
Analysis of the stimulus begins with the sense
receptors and works up to the level of the brain
and mind.
Letter “A” is really a black blotch broken down into
features by the brain that we perceive as an “A.”
7
Top-Down Processing
Information processing guided by higherlevel mental processes as we construct
perceptions, drawing on our experience and
expectations.
THE CHT
8
Bottom-Up vs. Top-Down
• When an interpretation emerges from the
data, this is called data-driven or bottom-up
processing. You want the interpretation of a
scene to be determined mostly by
information from the senses, not by your
expectations.
• In general, top-down processing—
information processing based on previous
knowledge or schemata—allows us to make
inferences: to "perceive" or "know" more
than is contained in the data.
Selective Attention
• Cocktail party effect:
• filtering out all other noises and
focusing on one conversation.
• When filtering out all
other noises, the
phenomenon of attention
being drawn by the sound
of your name, or other
interesting sounds.
Selective Attention
Selective Attention and Accidents
• Cell phone use and car
accidents
Selective Attention
Selective Inattention
• Inattentional blindness is a
psychological lack of attention and is
not associated with any vision
defects or deficits. It may be further
defined as the event in which an
individual fails to recognize an
unexpected stimulus that is in plain
sight.
• How many passes?
• In most groups, 50% of the subjects
did not report seeing the gorilla. The
failure to perceive the anomalies is
attributed to the failure to attend to it
while engaged in the difficult task of
counting the number of passes of the
ball. These results indicate that the
relationship between what is in one's
visual field and perception is based
much more on attention than was
previously thought.[
• Although it was found that 50% of the test
subjects demonstrated change blindness to
the introduction of the gorilla or the
umbrella, it is difficult to find published
information on what percentage of study
participants were able to accurately count
the passes.
• The basic study was re-used on British
television as a PSA designed to point out
the potential dangers to cyclists caused by
inattentional blindness in motorists.
Selective Attention
Selective Inattention
• Change blindness
• Change deafness
• Choice blindness
Stimuli we are sensitive to
• Smell and taste molecules in air and
saliva
• Feel temperature on skin
• Hear sound pressure waves
• See electromagnetic waves
• Feel pressure on skin
• Sense acceleration of one’s head
The physical world and
the psychological world
Physical variables can be measured
Psychological variables can only be reported
Sound pressure level -------- Loudness
Frequency --------- Pitch
Luminosity ---------------------- Brightness
Temperature ?
Smell
Skin pressure
Mapping between Worlds
A physical variable X may be lawfully related to a psychological variable Y
We can explore the relationship between
Physical properties
Collection of that data
Psychophysics
Subjective Experience
Basic Questions
• Detection
• What is the minimum intensity we can detect ?
• Recognition
• What is the signal we detect ?
• Discrimination
• How different must 2 stimuli be before they no
longer appear the same ?
• Scaling
• What is the relationship between stimulus
intensity & sensation & perception ?
Detection
Absolute Threshold
The minimum amount of energy in a sensory stimulus that is detected 50% of the time
So if the stimulus is subliminal what is the detection rate?
Just Notable Difference – JND
The smallest change in sensation that a person is able to detect 50% of the time.
This produces a …
Difference Threshold
The amount of stimulus needed detect a difference 50 % Of the time
Absolute Thresholds in our Senses
1. Vision, a candle flame 30 mile(s) away on a clear night
2. Hearing, a watch ticking 20 feet away
3. Taste, 1 teaspoon of sugar dissolved in 2 gallons of water
4. Smell, a single drop of perfume in a
three room house .
5. Touch, a bee’s wing falling a distance of 1 cm onto your cheek.
Difference Threshold
The amount of stimulus needed to detect a difference 50 %
of the time
Just Noticeable Difference (JND)
Weber’s Law
As the stimulus increases, the JND
increases at a constant rate.
Fetchner’s Law
As the physical intensity of a
Stimulus increases, our
Perception increases rapidly at
First then more slowly
Weber’s Law
Scaling: Steven’s Power Law
• Perceived intensity = physical intensity X constant
power for each type of judgment
• For instance, to perceive a light as twice as bright, its actual
intensity has to be increased between and 8 and 9 times
• Likewise, if an electric shock is doubled in intensity, we
perceive it as being about 10 times more intense
• Sensory adaptation to repetitive or unchanging
stimuli
• Survival and economy: it is more important to detect new
stimuli (which may signal danger) than constant stimuli
Signal Detection Theory
Stimulus
detected
Stimulus
undetected
Stimulus
present
Hit
Miss
Stimulus
absent
False alarm
Correct
rejection
Detection of a stimulus also depends on psychological factors,
such as personality, motivation, and past experiences.
Stimulus detected
Stimulus undetected
Stimulus present
Hit
Miss
Stimulus absent
False alarm
Correct rejection
With up to two partners on one piece of paper
1A A stream has just been stocked w/ fish. A fisherman who has been
unsuccessful at this location in the past only tries for 5 minutes
1B he then travels to a nearby pond that has no fish in it. A minute after
throwing in his line snags what he thinks is a big fish. It is actually a
boot.
2A.A baby sitter detects frightening noises after watching a scary movie.
The noise is the trees rustling in the wind
2B The next day she is at soccer practice. She does not detect the trees
nearby making the same noise.
3.You design the scenarios: A young person goes to the local dance
club in hopes of meeting someone nice to date.
In the mind
Knowledge
Recognition
Perception
subjective
Processing
Action
objective
Environmental
stimulus
Transduction
Stimulus on
receptors
In the head
Attended
stimulus
In the
world
Bell Work
• What is the difference between a twodimensional figure and a threedimensional figure?
Objective
• After watching Bob Ross paint his
“Happy Little Trees,” students will
identify and analyze the use of depth
cues.
Size Constancy
• Size constancy refers to the fact
that our perceptions of the size
of objects are relatively
constant despite the fact that
the size of objects on the retina
vary greatly with distance.
Take a look at the photograph and see if all
the people in it all look reasonably the
same size.
Ponzo Illusion
Depth Cues
• There is no actual depth in the artwork.
• Disparity arises from the fact that our two
eyes have a slightly different view of the
world. To allow you to see disparity requires
either real depth or two images developed
as if from different positions like our eyes.
• Monocular depth cues: Light and Shadow
The Cone
• Interposition is the partial blocking of a more distant
object by a nearer object.
• Check the small figure with the word interposition.
There are two rectangles with the farther rectangle,
lower and to the right, partially obscured by the
nearer one, right?
• Well, actually both rectangles are at the same
distance (the distance of the screen from your eyes).
It is the interposition, overlap, that causes the sense
of depth to arise. Usually the impression of depth
caused by interposition alone is not very strong.
Relative Height
• This cue can lead to a powerful sense of depth as seen in
this landscape.
• As there are not any objects, nor any interposition, nor any
real strong texture, the primary cues to depth being used in
this picture is relative height.
• The general rule is that the closer to the level of the
horizon, the farther away the object appears.
Relative Size
• The more distant an object is, the smaller the image of
that object will be on your retina, the back of the eye
where we really begin to "see.”
• The closer boat is painted much larger than the other.
Even the two paddles near each other show the use of
relative size.
• The boater in the
background does not
look abnormal in any
way. Despite being
painted smaller, the
person does not look
like a midget.
Texture Gradient
• The farther away the object is, the less
textured it is and the less detailed it is.
Shadow
Look at the large center bump.
Is it raised or indented?
Bob Ross
How does Bob Ross use the following to
create the perception of depth?
•
•
•
•
•
Interposition
Relative Height
Relative Size
Texture Gradient
Shadow