Topic: Autobiographical Psychosocial History
tutorthammy
Sensation_and_Perception_Crot.pptxSensation and Perception
Psy 150 - Crot
If she meets you once, she’ll recognize you the next time she sees you—even if it’s decades later.
For a woman known as C.S., recognizing someone she’s seen before is the norm. In fact, she—like a very few other individuals—can recognize faces of people she met years ago, sometimes only in passing. These “super-recognizers,” as they are called, excel at perceiving and later recalling faces.
One super-recognizer said she had identified another woman on the street who served her as a waitress five years earlier in a different city. Often, super-recognizers are able to recognize another person despite significant changes in appearance, such as aging or a different hair color.
But being a super-recognizer is a mixed blessing. As one woman with this ability says, “It doesn’t matter how many years pass, if I’ve seen your face before I will be able to recall it.” In fact, she sometimes pretends she doesn’t recognize a person, “because it seems like I stalk them, or that they mean more to me than they do when I recall that we saw each other once walking on campus four years ago in front of the quad!” (Munger, 2010; Russell, Duchaine, & Nakayma, 2010)
Most of us are reasonably good at recognizing people’s faces, thanks in part to regions of the brain that specialize in perceiving facial patterns. Super-recognizers represent a small minority of people with extraordinary abilities to perceive faces. At the other extreme are people with faceblindness, an equally rare disorder that makes it extremely difficult for them to recognize faces at all—even those of friends and family.
Conditions such as super-recognition and faceblindness illustrate how much we depend on our senses and our perceptual abilities to function normally. Our senses offer a window to the world, providing us with not only an awareness, understanding, and appreciation of the world’s beauty, but alerting us to its dangers. Our senses enable us to feel the gentlest of breezes, see flickering lights miles away, and hear the soft murmuring of distant songbirds.
This week, we focus on the field of psychology that is concerned with the ways our bodies take in information through the senses and the ways we interpret that information. We will explore both sensation and perception briefly today.
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Introduction
To a psychologist interested in understanding the causes of behavior, sensation and perception are fundamental topics because so much of our behavior is a reflection of how we react to and interpret stimuli from the world around us. The areas of sensation and perception deal with a wide range of questions—among them,
How we respond to the characteristics of physical stimuli.
What processes enable us to see, hear, and experience pain.
Why visual illusions fool us; and how we distinguish one person from another.
Introduction
Although intimately related, sensation and perception play two complimentary but different roles in how we interpret our world.
Sensation refers to the process of sensing our environment through touch, taste, sight, sound, and smell.
A stimulus is any passing source of physical energy that produces a response in a sense organ.
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.
To consider how psychologists understand the senses and, more broadly, sensation and perception, we first need a basic working vocabulary. In formal terms, sensation is the activation of the sense organs by a source of physical energy. Perception is the sorting out, interpretation, analysis, and integration of stimuli carried out by the sense organs and brain. A stimulus is any passing source of physical energy that produces a response in a sense organ.
Again, sensation encompasses the processes by which our sense organs receive information from the environment. Perception is the brain’s and the sense organs’ sorting out, interpretation, analysis, and integration of stimuli.
Although perception clearly represents a step beyond sensation, in practice it is sometimes difficult to find the precise boundary between the two. The primary difference is that sensation can be thought of as an organism’s first encounter with a raw sensory stimulus, whereas perception is the process by which that stimulus is interpreted, analyzed, and integrated with other sensory information. For example, if we were considering sensation, we might ask about the loudness of a ringing fire alarm. If we were considering perception, we might ask whether someone recognizes the ringing sound as an alarm and identifies its meaning.
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Isabel and Thanksgiving Dinner
As Isabel sat down to Thanksgiving dinner, her husband carried the
turkey in on a tray and placed it squarely in the center of the table.
The noise level, already high from the talking and laughter of family
members, grew louder still. As Isabel picked up her fork, the smell of
the turkey reached her and she felt her stomach growl hungrily. The
sight and sound of her family around the table, along with the smells
and tastes of the holiday meal, triggered happy childhood memories
and put Isabel in a relaxed, contented mood.
Put yourself in this setting and consider how different it might be if any one of your senses was not functioning. What if you were blind and unable to see the faces of your family members or the welcome shape of the golden-brown turkey? What if you had no sense of hearing and could not listen to the conversations of family members or were unable to feel your stomach growl, smell the dinner, or taste the food? Clearly, you would experience the dinner very differently than would someone whose sensory apparatus was intact.
Moreover, the sensations mentioned above barely scratch the surface of sensory experience. Although perhaps you were taught, as I was, that there are just five senses—sight, sound, taste, smell, and touch—that enumeration is too modest. Human sensory capabilities go well beyond the basic five senses. For example, we are sensitive not merely to touch but to a considerably wider set of stimuli—pain, pressure, temperature, and vibration, to name a few.
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Sensory Systems
Vision
Hearing
Smell
Taste
Vestibular sense (balance)
Kinethesis (body movement)
Touch (pressure, pain, temperature)
Vision
Visual receptor cells located on retina:rods for night vision and cones for color vision
The eye captures light and focuses it on the visual receptors, which convert light energy to neural impulses sent to the brain
Hearing
Audition (hearing) occurs via sound waves, which result from rapid changes in air pressure caused by vibrating objects
Receptors located in the inner ear (cochlea) tiny hair cells that convert sound energy to neural impulses sent along to brain
Smell and Taste
Smell receptors are located at top of nasal cavity
Taste receptors are taste buds on tongue. Four basic tastes: sweet, salty, sour and bitter
Body Senses
Sense of balance results from receptors in inner ear
Kinethesis - (body posture, orientation, and body movement) results from receptors in muscles, joint and tendons
Skin senses detect touch (pressure, temperature and pain)
Interaction of sensory information: Vision and balance (10
mins)
These exercises demonstrate how our brain utilizes visual and vestibular information in helping
us to maintain balance.
1. Everyday balance
1. Ask students to stand up and to make sure that each person has a bit of
space because they're going to be doing balancing
2. Ask students how is it they remain standing, without falling over - and
without even thinking consciously about it - what sensory and perceptual
processes are occurring? Through facilitated discussion, guide students
towards realising that it is probably via a combination of visual
information (e.g., information about the horizon) and the inner ear's
vestibular system (which works like a spirit level). In addition, students
may identify touch with pressure for example on one side of the foot
indicating leaning.
2. Challenging the vestibular system: One-foot balances with eyes open and
closed
1. 1 foot, open eyes: Have students stand on one foot for 30 seconds with
their eyes open
2. 1 foot, closed eyes: ...and then with them shut. The latter is more difficult
because the vestibular and visual systems work together to enable us to maintain balance.
With their eyes closed, students are relying only on their vestibular system.
3. 1 foot, closed eyes, dizzy: Ask students to spin around a few times (thus disrupting their
vestibular sense), then close their eyes and balance on one leg - they will find it impossible
as the vestibular system can no longer provide the information they need.
3. Challenging the visual system: One-foot balances, one eye, visual distortion
1. Have students stand on one foot.
2. Have them open the eye on the same side as the foot they are standing on and look at some
convenient point or object. The other eye should be closed.
3. Very carefully and gently press with their index finger on the same side of their open eye
against the eyelid of that eye. As they gently displace the eyeball toward their nose, they should continue looking
at the object. Immediately they will begin to lose balance and sway to the side of the open eye / finger.
4. Swap sides (i.e., open eye, leg, and finger). Their upper body automatically sways
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Absolute Thresholds
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.
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Approximate thresholds for five senses
Vision - candle flame at 30 miles on a dark clear night
Hearing - a ticking watch at 20 ft under quiet conditions
Taste - a tsp of sugar in 2 gallons of water
Smell - one drop of perfume diffused throughout 3 rooms
Touch - wing of a fly falling on cheek from 1 cm
Difference Thresholds: Noticing Distinctions between Stimuli
Suppose you wanted to choose the six best apples from a supermarket display—the biggest, reddest, and sweetest apples. One approach would be to compare one apple with another systematically until you were left with a few so similar that you could not tell the difference between them.
At that point, it wouldn’t matter which ones you chose.
Psychologists have discussed this comparison problem in terms of the difference threshold, the smallest level of added (or reduced) stimulation required to sense that a change in stimulation has occurred. Thus, the difference threshold is the minimum change in stimulation required to detect the difference between two stimuli, and so it also is called a just noticeable difference (Nittrouer & Lowenstein, 2007; Qin et al., 2010).
The stimulus value that constitutes a just noticeable difference depends on the initial intensity of the stimulus. The relationship between changes in the original value of a stimulus and the degree to which a change will be noticed forms one of the basic laws of psychophysics: Weber’s law. Weber’s law (with Weber pronounced “vay-ber”) states that a just noticeable difference is a constant proportion of the intensity of an initial stimulus.
Weber’s law helps explain why a person in a quiet room is more startled by the ringing of a telephone than is a person in an already noisy room. To produce the same amount of reaction in a noisy room, a telephone ring might have to approximate the loudness of cathedral bells. Similarly, when the moon is visible during the late afternoon, it appears relatively dim—yet against a dark night sky, it seems quite bright.
For example, Weber found that the just noticeable difference for weight is 1:50. Consequently, it takes a 1-ounce increase in a 50-ounce weight to produce a noticeable difference, and it would take a 10-ounce increase to produce a noticeable difference if the initial weight were 500 ounces.
Weber’s law: Difference threshold (15 mins)
1. Get students to form into groups.
2. Give each group two envelopes and ask them to put one 20c piece in one envelope and two 20c pieces in the other.
3. Invite each member of the group to hold both envelopes, one in each hand. They should be able to easily distinguish
which is the heavier envelope.
4. Now ask for a volunteer in each group to take off their shoes (or use two textbooks if
they don’t want to take off their shoes). Get the students to put one envelope in each shoe
or each textbook. Now if they hold one shoe/textbook in each hand they will find that it
is no longer easy to say which is heavier. Because the shoes weigh more, the difference
between the shoes must be greater for us to notice the difference.
5. Weber’s law: Difference thresholds grow with the magnitude of the stimulus, because
the difference is a percentage of the magnitude of the stimulus, not a constant amount.
6. Ask students for examples of Weber's principle in their everyday life
7. See also: Weber-Fechner law, Weber's law
(http://www.richardbrice.net/webers_law.htm)
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Signal Detection
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.
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Sensory Adaptation: Turning Down Our Responses
Adaptation- decreased sensory response to continuous stimuli
This 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?
You enter a movie theater, and the smell of popcorn is everywhere. A few minutes later, though, you barely notice the smell. The reason you acclimate to the odor is sensory adaptation. Adaptation is an adjustment in sensory capacity after prolonged exposure to unchanging stimuli. Adaptation occurs as people become accustomed to a stimulus and change their frame of reference. In a sense, our brain mentally turns down the volume of the stimulation it’s experiencing (Calin-Jageman & Fischer, 2007; Willert, & Eggert, 2011).
Some other examples of sensory adaptation or the “turning down our responses” are:
If you were to hear a loud tone over and over again, eventually it would begin to sound softer.
Similarly, although jumping into a cold lake may be temporarily unpleasant, eventually we probably would get used to the temperature.
This apparent decline in sensitivity to sensory stimuli is due to the inability of the sensory nerve receptors to fire off messages to the brain indefinitely. Because these receptor cells are most responsive to changes in stimulation, constant stimulation is not effective in producing a sustained reaction (Wark, Lundstrom, & Fairhall, 2007).
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Perception
“…a constructive process by which we go beyond the stimuli that are presented to us and attempt to construct a meaningful situation”.
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Perception involves organization and interpretation of sensory input
Creates meaning of sensory information
Perception occurs in the brain- sensation is in the pns
Interpretation of sensory information is an active process
Perceptions can differ among people-our perception are influenced by many things - experiences, motivations, expectancies
Sens/percep are inseparable, automatic processes
Perceptual Constancy
Size constancy
Shape constancy
Brightness constancy
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Imagine if every time an object changed we had to completely reprocess it. The next time you walk toward a building, you would have to re-evaluate the size of the building with each step, because we all know as we get closer, everything gets bigger. The building which once stood only several inches is now somehow more than 50 feet tall.
Luckily, this doesn't happen. Due to our ability to maintain constancy in our perceptions, we see that building as the same height no matter what distance it is. Perceptual constancy refers to 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 refers to 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: Everybody has seen a plate shaped in the form of a circle. When we see that same plate from an angle, however, it looks more like an ellipse. Shape constancy allows us to perceive that plate as still being a circle even though the angle from which we view it appears to distort the shape.
Brightness constancy refers to our ability to recognize that color remains the same regardless of how it looks under different levels of light. That deep blue shirt you wore to the beach suddenly looks black when you walk indoors. Without color constancy, we would be constantly re-interpreting color and would be amazed at the miraculous conversion our clothes undertake.
Perceiving Distance
We determine distance using two different cues: monocular and binocular.
Monocular cues are those cues which can be seen using only one eye. They include size; texture, overlap, shading, height, and clarity.
Binocular cues refer to those depth cues in which both eyes are needed to perceive. There are two important binocular cues; convergence and retinal disparity.
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With Monocular cues…..Size refers to the fact that larger images are perceived as closer to us, especially if the two images are of the same object. The texture of objects tend to become smoother as the object gets farther away, suggesting that more detailed textured objects are closer. Due to overlap, those objects covering part of another object is perceived as closer. The shading or 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. 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. 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 (clarity).
