Sensation and Perception
I. Introduction A. Some people can see perfectly, but cannot recognize members of their family. This
person has what’s called prosopagnosia, AKA “face blindness.” This illustrates the difference
between sensation and perception. 1. Sensation is the ability to see in this case, but includes
hearing, touching, tasting, and smelling. 2. Perception is how we put the impulses received from our
senses together so they make sense. Although a person may see perfectly, they cannot perceive or
correctly process the impulses so that they make sense. B. Sensation is part of bottom-up processing
where our senses send information to our brain. C. Perception is part of top-down processing where
our brain assembles the info to make sense of the impulses being sent to it. II. Selective attention A.
We sense a lot of information. Scientists estimate we observe 11,000,000 bits of info per second. But
we weed out all but 40 bits. B. The ability to screen out sensory information and focus on only a
small portion of it is called selective attention. Think of a housewife telling her husband the things
that need to be done around the house while he’s watching a football game on TV oblivious to
what’s she’s saying. He’s got selective attention. 1. The cocktail party effect is a person’s ability to
single out one voice amidst many others, then to “change channels” to another voice. A person in a
crowded, talking room can weed out other voices and converse with one person. Then the first
person can single out another voice and “tune in” on that person if desired. 2. Selective attention is
seen in car crashes. People that talk or text on the phone are distracted by the phone and are much
more likely to crash (4 times more in one study for talking, 23 times more for texting). More
specifically than “being distracted”, they selectively put their attention on one task at a time, driving
or texting, and the other suffers. 3. Despite people’s claim of “multi-tasking”, as humans, we focus
on one thing at a time. C. On the flip side is selective inattention or inattentional blindness. This is
the ability to purposefully block out all but one bit of sensory input - to focus on one thing only. 1.
This was seen in an experiment where a person in a gorilla suit walked among people passing a
basketball. The observers were to count basketball passes so they focused on that task. Most people
never saw the gorilla. D. Similarly, there is change blindness which is where people won’t notice a
change in “scenery” after a brief interruption. 1. This was seen in a scene where person A was
getting directions from a bystander, then was interrupted by construction workers, then was
replaced with person B. The bystander doesn’t notice the switch from person A to person B 40% of
the time. E. In choice blindness, people are unaware of the choices or preferences they make. 1. This
was seen in an experiment where women were shown two pictures and asked to choose the most
attractive person. Then they were tricked and shown the one they’d rejected and asked, “Why’d you
choose this person as more attractive.” 2. Only 13% caught the switcheroo. They explained why they
chose that person. 3. When asked if they’d recognize a switcheroo, 84% said they’d catch a switch.
This became known as choice blindness blindness – they can’t see that they’re choice blind. F. In
pop-out, something is noticeably different from the others and thus, pops out to the viewer. Imagine
a picture of a hundred white cats and one black dog. The black dog would pop out to you. III.
Thresholds A. We sense only a sliver of the info coming at us. We can’t see everything (like Xrays or
radio waves) or hear everything (the family dog can hear much more than us). B. Take sound for
example, at some point there is a point where we can’t hear a frequency (but the dog still can). This
cut-off point to sensation is called the absolute threshold. It’s defined as the minimum stimulation
needed to detect light, a sound, a pressure, taste or odor 50% of the time. 1. As an example, people
lose the ability to hear high-pitched as they grow older. 2. Teens use this to set “mosquito” ringtones
that adults likely won’t hear. Businesses use this to shoo away loitering teens. 3. Signal detection
theory is the idea that predicting whether or not we detect a stimulus depends not only on the
, stimulus, but also on our experience, expectations, motivation, and alertness. a. People in life-or-
death situations, like war, often have heightened signal detection. C. Subliminal stimulation (kin to
“subliminal perception”) is stimulation just below our level of consciousness. This occurs when we’re
subjected to a stimulus, but we just aren’t aware of it. For instance, an image might be flashed so
quickly we don’t even know we saw it. 1. Can we sense these things? By definition, yes, because
absolute threshold is 50% of the time. Thus, we might sense this 49% of the time. 2. Can these
unconscious stimuli impact our behavior? We’re not sure the answer to this question just yet. a. In
one study, subliminal stimuli can prime or prepare responses. This means a subliminal stimulus
prepared people for a response to a second stimulus. D. A difference threshold or just noticeable
difference (JND) is the minimum difference between two stimuli that can be detected at least 50% of
the time. 1. For example, imagine picking up a 20 pound weight and then a 20 pound 1 ounce
weight, you likely would not notice a difference. If you kept increasing the weight, you’d eventually
say, “This is heavier.” At some weight, you’d notice it 50% of the time, that’s the JND. 2. Weber’s
Law says the difference between two stimuli must differ by a constant proportion, not necessarily a
constant amount. a. Think about weight, weight must differ by 2% for a person to notice the
difference. b. Think about sound, two tones must differ by 0.3% for a person to notice the
difference. IV. Sensory adaptation A. Sensory adaptation is a person’s diminishing sensitivity to a
sensory stimulus. In other words, if a stimulus persists, you get used to it. 1. Think of a person
spilling a bit of perfume in class. You smell it strongly at first, but by the end of the class, you don’t
really notice it. As soon as the next class walks in, students say, “What’s that smell?” 2. This also
works for vision. Normally our eyes scan everything to “take it all in”. If you were forced to look at
the same thing over and over, you’d eventually stop seeing it. V. The stimulus input: light energy A.
The process where our eyes sense light energy and change it into neural messages that our brain can
handle is called transduction. B. Visual light makes up a very small portion of the electromagnetic
spectrum. But, that’s the part that we see. C. Visible light has two important characteristics… 1.
Frequency – Frequency refers to the wavelength of the light wave, or like waves on the beach, how
frequently they hit. Think of “FM” (frequency modulation) on the radio where a radio wave’s
wavelength is changed. 2. Amplitude – Amplitude refers to the intensity of the light wave, or like
waves on the beach, how strongly they hit. Think of “AM” (amplitude modulation) on the radio
where a radio wave’s amplitude is changed. VI. The stimulus input: light energy A. Vision is the
dominant sense in human beings. Sighted people use vision to gather information about their
environment more than any other sense. The process of vision involves several steps… 1. Step 1:
Gathering light a. The eyes transduce or convert light energy into neural messages. VII.The eye A.
Step 2: Within the eye 1. Cornea -The transparent protective coating over the front part of the eye.
2. Pupil -small opening in the iris through which light enters the eye. 3. Iris -colored part of the eye.
4. Lens -transparent part of the eye inside the pupil that focuses light onto the retina. 5. Retina -
lining of the eye containing receptor cells that are sensitive to light. Transduction occurs here. B.
Step 3: Transduction 1. Transduction – Process by which sensory signals are transformed into neural
impulses. 2. Receptor cell - Specialized cell that responds to a particular type of energy. 3. Rods -
Receptor cells in the retina responsible for night vision and perception of brightness. 4. Cones -
Receptor cells in the retina responsible for color vision. 5. Fovea - Area of the retina that is the
center of the visual field. 6. Optic nerve - The bundle of axons of ganglion cells that carries neural
messages from each eye to the brain. 7. Blind spot - Place on the retina where the axons of all the
ganglion cells leave the eye and where there are no receptors. 8. Optic chiasm - Point near the base
of the brain where some fibers in the optic nerve from each eye cross to the other side of the brain.
VIII. Visual information processing A. Step 4: In the Brain 1. The brain has specialized cells called
feature detectors. These cells specialized in exactly what they say - they detect features like angles,
lines, edges, and movements. 2. Unlike computers that use "serial processing" (they do operations
I. Introduction A. Some people can see perfectly, but cannot recognize members of their family. This
person has what’s called prosopagnosia, AKA “face blindness.” This illustrates the difference
between sensation and perception. 1. Sensation is the ability to see in this case, but includes
hearing, touching, tasting, and smelling. 2. Perception is how we put the impulses received from our
senses together so they make sense. Although a person may see perfectly, they cannot perceive or
correctly process the impulses so that they make sense. B. Sensation is part of bottom-up processing
where our senses send information to our brain. C. Perception is part of top-down processing where
our brain assembles the info to make sense of the impulses being sent to it. II. Selective attention A.
We sense a lot of information. Scientists estimate we observe 11,000,000 bits of info per second. But
we weed out all but 40 bits. B. The ability to screen out sensory information and focus on only a
small portion of it is called selective attention. Think of a housewife telling her husband the things
that need to be done around the house while he’s watching a football game on TV oblivious to
what’s she’s saying. He’s got selective attention. 1. The cocktail party effect is a person’s ability to
single out one voice amidst many others, then to “change channels” to another voice. A person in a
crowded, talking room can weed out other voices and converse with one person. Then the first
person can single out another voice and “tune in” on that person if desired. 2. Selective attention is
seen in car crashes. People that talk or text on the phone are distracted by the phone and are much
more likely to crash (4 times more in one study for talking, 23 times more for texting). More
specifically than “being distracted”, they selectively put their attention on one task at a time, driving
or texting, and the other suffers. 3. Despite people’s claim of “multi-tasking”, as humans, we focus
on one thing at a time. C. On the flip side is selective inattention or inattentional blindness. This is
the ability to purposefully block out all but one bit of sensory input - to focus on one thing only. 1.
This was seen in an experiment where a person in a gorilla suit walked among people passing a
basketball. The observers were to count basketball passes so they focused on that task. Most people
never saw the gorilla. D. Similarly, there is change blindness which is where people won’t notice a
change in “scenery” after a brief interruption. 1. This was seen in a scene where person A was
getting directions from a bystander, then was interrupted by construction workers, then was
replaced with person B. The bystander doesn’t notice the switch from person A to person B 40% of
the time. E. In choice blindness, people are unaware of the choices or preferences they make. 1. This
was seen in an experiment where women were shown two pictures and asked to choose the most
attractive person. Then they were tricked and shown the one they’d rejected and asked, “Why’d you
choose this person as more attractive.” 2. Only 13% caught the switcheroo. They explained why they
chose that person. 3. When asked if they’d recognize a switcheroo, 84% said they’d catch a switch.
This became known as choice blindness blindness – they can’t see that they’re choice blind. F. In
pop-out, something is noticeably different from the others and thus, pops out to the viewer. Imagine
a picture of a hundred white cats and one black dog. The black dog would pop out to you. III.
Thresholds A. We sense only a sliver of the info coming at us. We can’t see everything (like Xrays or
radio waves) or hear everything (the family dog can hear much more than us). B. Take sound for
example, at some point there is a point where we can’t hear a frequency (but the dog still can). This
cut-off point to sensation is called the absolute threshold. It’s defined as the minimum stimulation
needed to detect light, a sound, a pressure, taste or odor 50% of the time. 1. As an example, people
lose the ability to hear high-pitched as they grow older. 2. Teens use this to set “mosquito” ringtones
that adults likely won’t hear. Businesses use this to shoo away loitering teens. 3. Signal detection
theory is the idea that predicting whether or not we detect a stimulus depends not only on the
, stimulus, but also on our experience, expectations, motivation, and alertness. a. People in life-or-
death situations, like war, often have heightened signal detection. C. Subliminal stimulation (kin to
“subliminal perception”) is stimulation just below our level of consciousness. This occurs when we’re
subjected to a stimulus, but we just aren’t aware of it. For instance, an image might be flashed so
quickly we don’t even know we saw it. 1. Can we sense these things? By definition, yes, because
absolute threshold is 50% of the time. Thus, we might sense this 49% of the time. 2. Can these
unconscious stimuli impact our behavior? We’re not sure the answer to this question just yet. a. In
one study, subliminal stimuli can prime or prepare responses. This means a subliminal stimulus
prepared people for a response to a second stimulus. D. A difference threshold or just noticeable
difference (JND) is the minimum difference between two stimuli that can be detected at least 50% of
the time. 1. For example, imagine picking up a 20 pound weight and then a 20 pound 1 ounce
weight, you likely would not notice a difference. If you kept increasing the weight, you’d eventually
say, “This is heavier.” At some weight, you’d notice it 50% of the time, that’s the JND. 2. Weber’s
Law says the difference between two stimuli must differ by a constant proportion, not necessarily a
constant amount. a. Think about weight, weight must differ by 2% for a person to notice the
difference. b. Think about sound, two tones must differ by 0.3% for a person to notice the
difference. IV. Sensory adaptation A. Sensory adaptation is a person’s diminishing sensitivity to a
sensory stimulus. In other words, if a stimulus persists, you get used to it. 1. Think of a person
spilling a bit of perfume in class. You smell it strongly at first, but by the end of the class, you don’t
really notice it. As soon as the next class walks in, students say, “What’s that smell?” 2. This also
works for vision. Normally our eyes scan everything to “take it all in”. If you were forced to look at
the same thing over and over, you’d eventually stop seeing it. V. The stimulus input: light energy A.
The process where our eyes sense light energy and change it into neural messages that our brain can
handle is called transduction. B. Visual light makes up a very small portion of the electromagnetic
spectrum. But, that’s the part that we see. C. Visible light has two important characteristics… 1.
Frequency – Frequency refers to the wavelength of the light wave, or like waves on the beach, how
frequently they hit. Think of “FM” (frequency modulation) on the radio where a radio wave’s
wavelength is changed. 2. Amplitude – Amplitude refers to the intensity of the light wave, or like
waves on the beach, how strongly they hit. Think of “AM” (amplitude modulation) on the radio
where a radio wave’s amplitude is changed. VI. The stimulus input: light energy A. Vision is the
dominant sense in human beings. Sighted people use vision to gather information about their
environment more than any other sense. The process of vision involves several steps… 1. Step 1:
Gathering light a. The eyes transduce or convert light energy into neural messages. VII.The eye A.
Step 2: Within the eye 1. Cornea -The transparent protective coating over the front part of the eye.
2. Pupil -small opening in the iris through which light enters the eye. 3. Iris -colored part of the eye.
4. Lens -transparent part of the eye inside the pupil that focuses light onto the retina. 5. Retina -
lining of the eye containing receptor cells that are sensitive to light. Transduction occurs here. B.
Step 3: Transduction 1. Transduction – Process by which sensory signals are transformed into neural
impulses. 2. Receptor cell - Specialized cell that responds to a particular type of energy. 3. Rods -
Receptor cells in the retina responsible for night vision and perception of brightness. 4. Cones -
Receptor cells in the retina responsible for color vision. 5. Fovea - Area of the retina that is the
center of the visual field. 6. Optic nerve - The bundle of axons of ganglion cells that carries neural
messages from each eye to the brain. 7. Blind spot - Place on the retina where the axons of all the
ganglion cells leave the eye and where there are no receptors. 8. Optic chiasm - Point near the base
of the brain where some fibers in the optic nerve from each eye cross to the other side of the brain.
VIII. Visual information processing A. Step 4: In the Brain 1. The brain has specialized cells called
feature detectors. These cells specialized in exactly what they say - they detect features like angles,
lines, edges, and movements. 2. Unlike computers that use "serial processing" (they do operations
