Sensation IV Unit

8/3/2019 Sensation IV Unit

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Sensation & Perception - When we smell a fragrant flower, are we experiencing a

sensation or a perception? In everyday language, the terms "sensation" and "perception'

are often used interchangeably.

However, as you will soon see, they are very distinct, yet complementary processes. In

this section, we will discuss some concepts central to the study of sensation and perception and then move on to discuss vision and the perception of pain (it is not

possible in the scope of these notes to discuss all the senses).

I. Sensations and Perceptions

Sensations can be defined as the passive process of bringing information from the

outside world into the body and to the brain. The process is passive in the sense that we

do not have to be consciously engaging in a "sensing" process.Perception can be definedas the active process of selecting, organizing, and interpreting the information brought

to the brain by the senses.A) HOW THEY WORK TOGETHER:

1) Sensation occurs:

a) sensory organs absorb energy from a physical stimulus in the environment.

b) sensory receptors convert this energy into neural impulses and send them to the brain.

2) Perception follows:

a) the brain organizes the information and translates it into something meaningful.

B) But what does "meaningful" mean? How do we know what information is importantand should be focused on?

1) Selective Attention - process of discriminating between what is important & is

irrelevant (Seems redundant: selective-attention?), and is influenced by motivation.

For example - students in class should focus on what the teachers are saying and the

overheads being presented. Students walking by the classroom may focus on people in

the room, who is the teacher, etc., and not the same thing the students in the class.

2) Perceptual Expectancy - how we perceive the world is a function of our past

experiences, culture, and biological makeup.For example, as an American, when I look ata highway, I expect to see cars, trucks, etc, NOT airplanes. But someone from a different

country with different experiences and history may not have any idea what to expect andthus be surprised when they see cars go driving by.

Another example - you may look at a painting and not really understand the message the

artist is trying to convey. But, if someone tells you about it, you might begin to see things

in the painting that you were unable to see before.



ALL OF THIS IS CALLED Psychophysics

C) Psychophysics can be defined as, the study of how physical stimuli are translated

into psychological experience.

In order to measure these events, psychologists use THRESHOLDS.

1) Threshold - a dividing line between what has detectable energy and what does not.

For example - many classrooms have automatic light sensors. When people have not been

in a room for a while, the lights go out. However, once someone walks into the room, the

lights go back on. For this to happen, the sensor has a threshold for motion that must becrossed before it turns the lights back on. So, dust floating in the room should not make

the lights go on, but a person walking in should.

2) Difference Threshold - the minimum amount of stimulus intensity change needed to

produce a noticeable change.

the greater the intensity (ex., weight) of a stimulus, the greater the change needed to produce a noticeable change.

For example, when you pick up a 5 lb weight, and then a 10 pound weight, you can feel a

big difference between the two. However, when you pick up 100 lbs, and then 105 lbs, it

is much more difficult to feel the difference.

3) Signal-Detection Theory - detection of a stimulus involves some decision making

process as well as a sensory process. Additionally, both sensory and decision making

processes are influenced by many more factors than just intensity.

a) Noise - how much outside interference exists.

b) Criterion - the level of assurance that you decide must be met before you take action.Involves higher mental processes. You set criterion based on expectations and

consequences of inaccuracy.

For example - at a party, you order a pizza...you need to pay attention so that you will beable to detect the appropriate signal (doorbell), especially since there is a lot of noise at

the party. But when you first order the pizza, you know it won't be there in 2 minutes, so

you don't really pay attention for the doorbell. As the time for the pizza to arriveapproaches, however, your criterion changes...you become more focused on the doorbelland less on extraneous noise.

II. SIGHT/VISION

A) the visual system works on sensing and perceiving light waves. Light waves vary in

their length and amplitude:



a) wave length (also referred to as frequency, since the longer a wave, the less

often/quickly it occurs) - affects color perception (ex., red=approx 700, yellow approx

600)

b) wave amplitude (this is the size/height of the wave) - affects brightness perception.

B) Structure of The EYE:

1) Cornea - the round, transparent area that allows light to pass into the eye.

2) Lens - the transparent structure that focuses light onto the retina.

3) Retina - inner membrane of the eye that receives information about light using rods

and cones. The functioning of the retina is similar to the spinal cord - both act as ahighway for information to travel on.

4) Pupil - opening at the center of the iris which controls the amount of light entering theeye. Dilates and Constricts.

5) Rods & Cones - many more rods (approximately 120 million) than cones (approx 6.4million).

a) cones - visual receptor cells that are important in daylight vision and color vision.

the cones work well in daylight, but not in dim lighting. This is why it is more difficult to

see colors in low light.

most are located in the center of the retina...called the FOVEA, which is a tiny spot in thecenter of the retina that contains ONLY cones...visual acuity is best here.

SO...when you need to focus on something you attempt to bring the image into the fovea.

b) rods - visual receptor cells that are important for night vision and peripheral vision.

the rods are better for night vision because they are much more sensitive than cones.

in addition, the rods are better for peripheral vision because there are many more on the

periphery of the retina. The cones are mostly in and around the fovea but decrease as you

go out.

to see best at night, look just above or below the object...this keeps the image on the rods.

C) Seeing In Color - we can see many colors, but only have 3 types of cones that receive

information about color. We have cones that pick up light waves for red, green, and blue.

Color Vision Theories:



1) Trichromatic Theory - this theory indicates that we can receive 3 types of colors (red,

green, and blue) and that the cones vary the ratio of neural activity (Like a projection

T.V.). The ratio of each each color to the other then determines the exact color that wesee.

2) Opponent-Process Theory - color perception depends on the reception of pairs of antagonist colors. Each receptor can only work with one color at a time so the opponent

color in the pair is blocked out. Pairs = red-green, blue-yellow, black- white (light-dark).

Note: Most every Introductory Psychology book has a demonstration on the Opponent-

Process theory. Please look for the one in your book and give it a try.

DOES COLOR EXIST? People just assume that because we see colors, that they actually

exist in the world. In other words, that when they see the color red, that red is a real, physical, tangible, "thing". But is it, or is color just a matter of our perception? If we had

different types of nervous systems, we would see things differently (literally) and so

wouldn't we think those other things we saw were the real "things"? Let's examine thisquestion of perception a bit further.

Sensation

Sensation is the process by which our senses gather information and send it to the brain. A large

amount of information is being sensed at any one time such as room temperature, brightness of

the lights, someone talking, a distant train, or the smell of perfume. With all this information

coming into our senses, the majority of our world never gets recognized. We don't notice radio

waves, x-rays, or the microscopic parasites crawling on our skin. We don't sense all the odors

around us or taste every individual spice in our gourmet dinner. We only sense those things we

are able too since we don't have the sense of smell like a bloodhound or the sense of sight like a

hawk; our thresholds are different from these animals and often even from each other.

Absolute Threshold

The absolute threshold is the point where something becomes noticeable to our senses. 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.

Difference Threshold

Once a stimulus becomes detectable to us, how do we recognize if this stimulus changes. When

we notice the sound of the radio in the other room, how do we notice when it becomes louder. It's

conceivable that someone could be turning it up so slightly that the difference is undetectable.

The difference threshold is the amount of change needed for us to recognize that a change has

occurred. This change is referred to as the Just Noticeable Difference.



This difference is not absolute, however. Imagine holding a five pound weight and one pound

was added. Most of us would notice this difference. But what if we were holding a fifty pound

weight? Would we notice if another pound were added? The reason many of us would not is

because the change required to detect a difference has to represent a percentage. In the first

scenario, one pound would increase the weight by 20%, in the second, that same weight would

add only an additional 2%. This theory, named after its original observer, is referred to as

Weber's Law.

Signal Detection Theory

Have you ever been in a crowded room with lots of people talking? Situations like that can make

it difficult to focus on any particular stimulus, like the conversation we are having with a friend.

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 detect what we want to focus

on and ignore or minimize everything else.

Sensory Adaptation

The last concept refers to stimuli which has become redundant or remains unchanged for an

extended period of time. Ever wonder why we notice certain smells or sounds right away and

then after a while they fade into the background? 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, after all, if it doesn't change, why do we need to constantly

sense it?

Sensory receptors are cells that are specialized for the task of transduction, or

converting physical energy into neural impulses. There are many different types of

sensory receptors, such as:

• Rods and cones in the retina, which transduce light.

• Cilla in the ear, which transduce sound

• Pressure, vibration, heat, and pain receptors in the skin

• Chemical receptors in the nasal cavities and mouth

• Muscle spindles

II) PERCEPTION



Perception is the process by which the mind selects, organizes, and interprets sensations.

Our eyes see, our ears hear, our hands touch--or do they? Without interpretation, there is

no point to sensation.

Much of our understanding of how and why we perceive things comes from Gestalt

Psychology

For example - one of the most well known Gestalt principles is the Phi Phenomenon,

which is the illusion of movement from presenting stimuli in rapid succession. When yousee a cartoon or running Christmas lights, you see movement (although none actually

exists) because of this principle.

A) Gestalt Principles of Perceptual Organization

1) figure-ground - this is the fundamental way we organize visual perceptions. When we

look at an object, we see that object (figure) and the background (ground) on which it

sits. For example, when I see a picture of a friend, I see my friends face (figure) and the beautiful Sears brand backdrop behind my friend (ground).

2) simplicity/pragnanz (good form) - we group elements that make a good form.

However, the idea of "good form" is a little vague and subjective. Most psychologiststhink good form is what ever is easiest or most simple. For example, what do you see

here: : > )

do you see a smiling face? There are simply 3 elements from my keyboard next to eachother, but it is "easy" to organize the elements into a shape that we are familiar with.

3) proximity - nearness=belongingness. Objects that are close to each other in physicalspace are often perceived as belonging together.

4) similarity - do I really need to explain this one? As you probably guessed, this one

states that objects that are similar are perceived as going together. For example, if I ask you to group the following objects: (* * # * # # #) into groups, you would probably place

the asterisks and the pound signs into distinct groups.

5) continuity - we follow whatever direction we are led. Dots in a smooth curve appear to

go together more than jagged angles. This principle really gets at just how lazy humansare when it comes to perception.

6) common fate - elements that move together tend to be grouped together. For example,

when you see geese flying south for the winter, they often appear to be in a "V" shape.

7) closure - we tend to complete a form when it has gaps.



B) Illusions - an incorrect perception caused by a distortion of visual sensations.

1) Muller-Luyer Illusion

2) Reversible Figures - ambiguous sensory information that creates more than 1 good

form. For example, the picture of two faces looking toward each other that is also a vase.I am sure most every Introductory Psychology book has this example.

3) Impossible Figures - objects that can be represented in 2-dimensional pictures but can

not exist in 3-dimensional space despite our perceptions. You know the artist, Escher

who draws the pictures like...the hands drawing each other, the waterfall that goes downand stays level at the same time, etc...

C) THE PERCEPTION OF PAIN

Pain is an unpleasant yet important function for survival: warning system (but not all pain

is needed for survival).

There are two different pathways to the brain on which pain can travel - information

brought from free nerve endings in the skin to the brain via two different systems:

1) fast pathways - registers localized pain (usually sharp pain) and sends the information

to the cortex in a fraction of a second. EX. - cut your finger with a knife.

2) slow pathways - sends information through the limbic system which takes about 1-2

seconds longer than directly to the cortex (longer lasting, aching/burning).

Factors in Pain Perception - not an automatic result of stimulation:

1) expectations - research shown that our expectations about how much something will

hurt can effect our perception.

Melzack - indicated that believing that something will be very painful helps us preparefor it.

For example - child birth: Lamaze method falsely leads us to believe it won't be painful.

Maybe if we know it will be bad we can adequately prepare to handle it.

another example - placebo effect - if we believe pain has stopped, it may.

2) personality - people with negative types of personalities often have more pain. E

For example - a very uptight person may experience muscle pains, back pains, etc.

http://www.alleydog.com/101notes/s&p.html#Muller-Lyer%20explained

http://www.alleydog.com/101notes/s&p.html#Muller-Lyer%20explained



3) mood - bad moods, angry, unhappy, etc, can lead to the experience of increased pain.

For example - study manipulated moods of subjects then asked them to complete

questionnaires of pain perception. Those in negative mood group reported significantlymore pain than other subjects.

So, it seems that our brains can regulate, control, determine, and even produce pain.

THEORIES OF PAIN PERCEPTION

1) Gate Control Theory (Melzack & Walls, 1965) - incoming pain must pass through a

"gate" located in the spinal cord which determines what information about pain will besent to the brain. So, it can be opened to allow pain through or closed to prevent pain

from being perceived.

The Gate - actually a neural network controlled by the brain. Located in an area of the

spinal cord called the Substansia Gelatinosa. There are two types of nerve fibers in thisarea:

a) large - sends fast signals and can prevent pain by closing the gate.

b) small - sends slower signals which open the gate. So - when pain occurs it is because

the large fibers are off and the small are on, opening the gate.

Since the gate is controlled by the brain, he factors discussed earlier (expectations, mood,

personality) influence the functioning of the gate.

Contradiction to Gate Control Theory:

1) endorphins - the body's own pain killers (morphine-like). May explain acupuncture,

acupressure, pain tolerance during last two weeks of pregnancy, etc.

BUT- endorphins may work with the gate control theory - maybe pain is perceived,

endorphins are released, so the brain no longer needs the signals and closes the gate.

PHANTOM LIMBS

ability to feel pain, pressure, temperature, and many other types of sensations including pain in a limb that does not exist (either amputated or born without).



the feelings and the pain are sometimes so life-like that person attempts to pick things up

with phantom hand, step with phantom foot or leg, etc. Often person feels phantom

moving in perfect coordination with the rest of the body - some report a missing armextending outward at a 90 degree angle so they turn sideways when going through a

doorway.

may occur right after amputation or not until years later.

often felt as part of the body (belonging to the rest of the body). EX. - with a missing leg,some report having a phantom foot but not the rest of the leg. Still, the foot feels as

though it is part of the body.

Go to Phantom Limb Pages - includes case studies

Explanations:

1) the neuroma explanation - remaining nerves in the stump grow into nodules(neuromas) at the end of the stump continue to fire signals. Signals follow the same

pathways the brain as when the appendage existed.

2) the spinal cord explanation - neurons in the spinal cord that are no longer receiving

information from the lost appendage continue to send information to the brain.

Problem - studies have shown that when areas in the spinal cord are severed oftenfeelings still being perceived from areas that meet the spinal cord in lower areas (below

separation in spinal cord).

3) the brain explanation - signals in the somatosensory circuits of the brain change whenthe limb is lost which produce the phantom...the brain compensates for the loss or alteredsignals. This has been expanded - brain contains a network of fibers that not only respond

to stimulation but continually generates a pattern of impulses that indicate that the body is

intact and functioning. Thus, the brain creates the impression that the limb exists and is alright. This system may be prewired.

4) the hardwired explanation - we may have a biological makeup to be born with all of

our appendages. So, when we are born w/o one or lose one, the nerves are still there and

are still going to send the information.

Please note that we can not cover ALL the senses in class so make sure you read abouttaste, touch, hearing, and smell in the book.

Muller-Lyer explained

http://www.alleydog.com/101notes/phantom1.html

http://www.alleydog.com/101notes/phantom1.html



Although many theories exist for this illusion, there is no certain explanation. One theory

is based on eye movement. When the arrows point inwards, our gaze rests inside the

angles formed by the arrows. When they point outwards, our eyes demarcate the entire perspective and our gaze rests outside the angles. The outward pointing arrows make the

figure more open and so the horizontal line appears longer.

The illusion takes its name from Franz Carl Müller-Lyer (1857-1916), who studied

medicine in Strasbourg and served as assistant director of the city's psychiatric clinic.

Müller-Lyer's main works were in the field of sociology. He himself attempted to explainthe illusion he had discovered as follows: "the judgment not only takes the lines

themselves into consideration, but also, unintentionally, some part of the space on either

side." He published two articles on the illusion bearing his name. ('Optical Illusions'

1889, and 'Concerning the Theory of Optical Illusions: on Contrast and Confluxion'1896)

Favreau (1977) studied a number of textbooks in which Müller-Lyer presented and

measured the figures. He noticed that in many cases, the figure had been drawn thewrong way round so that the illusion appeared more forceful!

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Sensation IV Unit