04.+Sensation+and+Perception

Everything that organisms know about the world is first encountered when stimuli in the environment activate sensory organs, initiating awareness of the external world. Perception involves the interpretation of the sensory inputs as a cognitive process. AP students in psychology should be able to do the following: • Discuss basic principles of sensory transduction, including absolute threshold, difference threshold, signal detection, and sensory adaptation. • Describe sensory processes (e.g., hearing, vision, touch, taste, smell, vestibular, kinesthesis, pain), including the specific nature of energy transduction, relevant anatomical structures, and specialized pathways in the brain for each of the senses. • Explain common sensory disorders (e.g., visual and hearing impairments). • Describe general principles of organizing and integrating sensation to promote stable awareness of the external world (e.g., Gestalt principles, depth perception). • Discuss how experience and culture can influence perceptual processes (e.g., perceptual set, context effects). • Explain the role of top-down processing in producing vulnerability to illusion. • Discuss the role of attention in behavior. • Challenge common beliefs in parapsychological phenomena. • Identify the major historical figures in sensation and perception (e.g., Gustav Fechner, David Hubel, Ernst Weber, Torsten Wiesel).
 * IV. Sensation and Perception (6–8%)**

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 defined as **//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 important and 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 at a 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 and thus 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.
 * I. Sensations and Perceptions**

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 be crossed 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 be able 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 arrive approaches, however, your criterion changes...you become more focused on the doorbell and 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 a highway for information to travel on. 4) Pupil - opening at the center of the iris which controls the amount of light entering the eye. Dilates and Constricts. 5) Rods & Cones - many more rods (approximately 120 million) than cones (approx 6.4 million). 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 the center 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 we see. > 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 this question of perception a bit further.
 * All of this is called Psychophysics**

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 you see 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 psychologists think 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 each other, 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 physical space 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 humans are 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 down and stays level at the same time, etc... >
 * II) PERCEPTION**

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 prepare for 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. 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 significantly more pain than other subjects. >> So, it seems that our brains can regulate, control, determine, and even produce pain. >> 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 be sent 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 this area: >> 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.
 * THEORIES OF PAIN PERCEPTION**

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 arm extending 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 often feelings 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 when the limb is lost which produce the phantom...the brain compensates for the loss or altered signals. 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 al right. 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 about taste, touch, hearing, and smell in the book.  Muller-Lyer explained 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 explain the 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 the wrong way round so that the illusion appeared more forceful!

**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?

**Perception**

As mentioned in the introduction, perception refers to interpretation of what we take in through our senses. The way we perceive our environment is what makes us different from other animals and different from each other. In this section, we will discuss the various theories on how our sensation are organized and interpreted, and therefore, how we make sense of what we see, hear, taste, touch, and smell.

**Gestalt Principles of Grouping**

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. This allows us to interpret the information completely without unneeded repetition. For example, when you see one dot, you perceive it as such, but when you see five dots together, you group them together by saying a "row of dots." Without this tendency to group our perceptions, that same row would be seen as "dot, dot, dot, dot, dot," taking both longer to process and reducing our perceptive ability. The Gestalt principles of grouping include four types: similarity, proximity, continuity, and closure.



Similarity refers to 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. In the next figure, 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 refers to our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern. In the third figure, although merely a series of dots, it begins to look like an "X" as we perceive the upper left side as continuing all the way to the lower right and the lower left all the way to the upper right. 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.

**Maintaining Perceptual Constancy**

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.

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.

**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**).

**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. **Convergence** refers to 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. Since 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.