Module 2 This is a single, concatenated file, suitable for printing or saving as a PDF for offline viewing. Please note that some animations or images may not work. Module 2: The Biological Level Monday, May 20 – Sunday, May 26 Required Reading/Viewing: Principles of Psychology, Chapters 3–4 (Pages 64–102; 122–145; 165–184) Module 2 online content interface (2011, October 16). Stress: Portrait of a Killer. A National Geographic Documentary (2008) [Video]. YouTube. Discussions: Module 2 Discussion Initial responses due Thursday, May 23, 9:00 AM ET Two peer response due Sunday, May 26, 9:00 AM ET Leader response due Tuesday, May 28, 9:00 AM ET Assignments: Film Response Worksheet 1 due Monday, May 27, 5:00 PM ET Live Classrooms: Monday, May 20, 7:30–9:00 PM ET Activity: Complete Module 2 Review and Reflect, due Monday, May 27, 11:59 PM ET Welcome to Module 2 cas_ps101_19_su2_mtompson_mod2 video cannot be displayed here. Videos cannot be played from Printable Lectures. Please view media in the module. Learning Objectives List methods for studying the brain and specify the advantages and disadvantages of each. Describe how brain cells function. List major brain regions and their functions. Describe the difference between “sensation” and “perception.” Describe the pathway through which light travels from the eye to the brain, allowing us to see images. List cues that we use to determine depth perception. Brain Introduction Think back to the introductory lecture when I introduced the “levels of analysis.” Today we are going to focus on the biological level. We are going to focus on the brain and how it underlies human behavior. In talking about the brain, it is important to distinguish between structure and function. The brain’s structure is how it is built, what it looks like, and what parts are included. human brain structure Its function is how those these parts work together to get the job done. Think of it like a car. The car’s structure includes its parts—spark plugs, braking system, etc. The car’s function is how, when you start it up, all the parts work together to move it forward. brain function according to area of the brain We are going to be focusing in this module on both structure and function. emoji of Dr. Tompson with the wrods, so Structure is all about the parts; function is how they work together Methods for Studying the Brain But first, let’s look at the big picture…how do we study the brain? There are many techniques, each with advantages and disadvantages. I’m going to review several, but this is certainly not a comprehensive or exhaustive list; more are being developed! Autopsy Here brains can be examined after death. As an example, Boston University has the largest repository of brain tissue in the world focused on studying CTE. What is CTE? Chronic Traumatic Encephalopathy. You may be aware that CTE has been of intense interest for some time now because of strong evidence that sports injuries, particularly those occurring on the football field, may lead to CTE. Advantages: Autopsies allow researchers to examine real human tissue and can tell us a lot about the structure of the brain. Disadvantages: The brain is dead, so we can’t see it at work. It’s like looking at a car that no longer runs. Although we can learn a lot about structure, we can’t learn much about function. Animal Models We are mammals; other mammals’ biological processes are similar. As an example, much has been learned by administering drugs (e.g., cocaine) to rats to examine their impact on behavior and on brain structure (after “sacrificing” the rat). As another example, in animal models the brain can be damaged in a very specific area (a specific lesion, we call it), and the impact of the damage can be studied. Advantages: Within certain ethical guidelines covering animal research, we can still conduct studies that we could not do with humans. Disadvantages: Sometimes it is hard to generalize to humans. We can’t easily replicate complex cognitive phenomena. For example, rats don’t learn to read, so we can’t look at how reading is learned in rats!! Testing Folks with Brain Damage These are “experiments of nature.” By understanding what happens when something goes wrong, we can learn about how the brain actually works. As an example, let’s say that a person has very specific damage in a certain area of the brain (maybe as a result of a stroke—a bleed in the brain). By carefully testing them we can learn so much about the impact of damage to that region on the individual’s behavior. We will talk a lot more about this when we talk about memory. Let me briefly describe the case of H.M. (so called to disguise his identity). H.M. had severe epilepsy (a seizure disorder) and had brain surgery to treat it; the doctors removed a particular region on both sides of his brain with the hope that it would improve his seizures. Unfortunately, very unfortunately, when he awoke he was no longer able to form ANY new memories about his life. Crazy as this sounds, he was able to have interactions with people daily and yet have to be introduced to them anew every day. Although he could remember things that happened prior to the surgery, no new memories (events after the surgery) could form. Sound horrifying? H.M. was tested extensively over the years, and this research greatly increased knowledge of the role of specific brain regions in forming new memories. Advantages: We can do these studies ethically and learn much. Disadvantages: The damage may not be as specific as we would need it to be to really understand fully the function of small areas (it is not a controlled experiment). There may be other (undetectable) damage influencing what is happening. The brain also undergoes changes AFTER damage; our brain may reorganize in some ways to compensate. The problems that lead to the damage in the first place (in H.M., seizures) may have changed the brain in some ways. CT Computerized tomography (CT) scanning builds up a picture of the brain based on the differential absorption of X-rays. Advantages: CT is relatively cheap and quick and is useful in revealing the gross features of the brain. For this reason it can be used in medicine to diagnose tumors, aneurysms, and other phenomenon. Disadvantages: CT has poor resolution and details cannot be seen clearly. EEG Electroencephalography (EEG) measures brain electrical activity by recording from electrodes placed on the scalp. The signal represents the electrical output from what we call the cortex of the brain. Example: EEG has been used to study the activity of the brain during sleep; we will talk about this a lot more later on in this course. It can also be done over extended periods of time. For example, in diagnosing seizure disorders, portable EEG equipment allows data on brain activity to be collected over a series of days, not just minutes or hours. Advantages: EEG has good temporal (in time or when) resolution (that is, it is capable of detecting changes in electrical activity in the brain on a millisecond-level), and it is one of the few techniques with such good temporal resolution. Disadvantages: It doesn’t have good spatial (where) resolution. So while we can determine when a change in activity took place, we cannot determine exactly where in the brain the change happened. PET Positron Emission Tomography (PET) uses trace amounts of short-lived radioactive material to map functional processes in the brain. When the material undergoes radioactive decay a positron is emitted, which can be picked up by the detector. Areas of high radioactivity are associated with brain activity. So you can see how specific chemical substances change during certain tasks. Example: PET has been used to look at certain kinds of deposits in Alzheimer’s disease—a primary cause of dementia. It’s helped us to understand the process of how this disease works. Advantages: PET can detect cellular level metabolic changes, so it is very specific. Particular radioactive tracers can be used to look at specific chemicals. Disadvantages: Many folks may not be comfortable with having an injection of a radioactive tracer. It’s also expensive. fMRI In fMRI, a very powerful magnet is used to detect changes in blood oxygenation and flow that occur in response to neural activity. Active brain areas consume more oxygen leading to increased blood flow. FMRI can be used to produce activation maps showing which parts of the brain are active during a particular mental process (for example, reading, listening to music, watching images on a screen). Example: We can look at which regions are active during certain tasks. Researchers at Harvard actually wanted to look at how individuals respond to parental criticism! They obtained audio recordings of individual subjects’ mothers criticizing them. The researchers then played the recordings to the subjects while they were in the fMRI scanner and examined which brain regions were active! Pretty interesting! Advantages: FMRI can assess changes during specific tasks (i.e., memory tasks, watching videos, making ratings), because it has pretty good temporal resolution—the brains response is close in time to the event. Disadvantages: FMRI is very sensitive to movement; the study subject has to stay very still in the scanner! This sensitivity to movement makes it hard to do fMRI with children, as they aren’t so good at staying still. That said, strategies have been developed to help kids feel comfortable and to get good fMRI data. It’s also a little disconcerting to be in the scanner, as it is a pretty tight space. If you have claustrophobia (a fear of closed-in spaces), fMRI is pretty distressing! It’s also expensive. Now that we’ve reviewed some of the major techniques for studying the brain, let’s focus on some of what we know. We are going to focus on structure and function by examining individual neurons (nerve cells) and neuroanatomy (the major structures of the brain). Brain Cells and Their Function Let’s focus on neurons. The average brain has about 100 billion neurons! In addition, there are many other cells that support and protect your brain. neuron So, what are some of the major parts of the neuron. First, on the left side of the image are the dendrites. Remember that there are other neurons further to the left and right (this is just one cell). The dendrites take in information from the adjacent cells. That information is merged in the cell body, which then sends an electrical signal down the axon. The axon is coated by a substance called myelin. Myelin speeds the rate of electrical transmission down the axon. Interestingly, there is much less myelin on the axons of the brain during infancy; over the first two years of life, neuronal axons are acquiring myelin, making transmission of messages much faster. The child rapidly becomes more capable of a variety of activities and responses. We also see lots of myelination during the adolescent years—a period of rapid brain development. During adolescence, neuronal transmission becomes much faster and more efficient—adolescents are becoming better and faster thinkers! We will get back to this. Back to the electrical signal coming down the axon: As the axon comes to an end, it begins to branch out. When the electrical signal gets to the end of these axon branches, the signal needs to get to the next cell. This is where the process changes from an electrical one to a chemical one. This is why we refer to neural transmission as an electro-chemical process. The terminal endings do not actually touch the dendrites of the next cell. There is a gap between the terminal ending of the axon and the dendrite of the next cell, and we refer to this tiny gap as the synapse. So here’s what’s happening with synaptic transmission, that is, transmission across that gap or synapse. Within each axon terminal ending there are tiny pockets of a chemical substance or neurotransmitter that is produced by the cell; these tiny pockets that store the neurotransmitters are called vesicles. The nerve impulse stimulates these vesicles to move to the end of the terminal button and to release their contents into the synapse. These neurotransmitters then attach to specific receptor sites on the dendrite of the next cell—we call this next cell the postsynaptic neuron. Some neurotransmitters are excitatory—tthey increase the likelihood that the next neuron will fire (send an electical signal down its axon); some are inhibitory—they decrease the likelihood that the next neuron will fire. It is the sum of all of the inputs that determines what will happen (to fire or not to fire, that is the question!). synaptoc transmission Here is a different view of the synaptic transmission. So, what happens to the neurotransmitter substance after it is released into the synapse? There’s leftover in the synapse; what happened to it? Well, two things can happen. First is a process we call reuptake. In reuptake the neurotransmitter substance is taken back into the cell from which it was originally released. It can then be used again in the future. I think we can consider this the brain using recycling. Second is a process called degradation. Your brain is a small but efficient chemical factory, producing many substances. In addition to neurotransmitters, it also produces a number of enzymes. Some of these enzymes are involved in the process of degradation, and they essentially come in and "clean up" the leftover neurotransmitter. When I think of this, I imagine them as little street sweepers, getting rid of the old junk and mess. Implications: Neurons, Medical Disorders, and Medical Treatments So why is all this important? It’s important at the level of basic and applied science. moji of Dr. Tompson with the words, By understanding how the brain works we can understand diseases and drug actions I think the best approach to thinking about this question is to use examples. A couple of interesting examples help us to explain some behavioral disorders. How many of you know what multiple sclerosis or MS is? MS is an autoimmune disorder in which the immune system attacks myelin on neuronal axons. The myelin is broken down, and this impacts the rate of neural transmission. Individuals with MS experience a range of symptoms, including changes in vision and difficulties with motor activities. The effects of MS will vary depending on which neuronal axons are most affected, and the symptoms of MS can vary between individuals. multiple sclerosis As another example, too much or too little neurotransmitter can cause problems. The neurotransmitter substance dopamine is involved in a number of important functions. You may have heard about the pleasure center of the brain, which is a dopamine-rich area in the midbrain (we will talk about the midbrain a little bit later). Stimulation of dopamine neurons in this part of the brain leads to feelings of pleasure. In Parkinson’s disease, we see the death of dopamine cells in a particular part of the midbrain called the nigra striatum. The nigra striatum is essential in movement. One of the main symptoms we see in Parkinson’s disease is difficulties with movement. The death of those dopamine cells underlies the symptoms we see in Parkinson’s disease. Parkinson's Disease Let’s focus a little bit more on dopamine. Let me take a little bit of a side trip. How many of you have heard of schizophrenia? Schizophrenia is what many people think of when they think of “mental illness.” Indeed, schizophrenia is a severe mental illness in which individuals experience perceptual distortions, including hallucinations, and may develop delusions, which are odd beliefs not based in fact, including severe paranoia. One of the major theories about schizophrenia is known as the dopamine hypothesis. This is the idea that too much dopamine neurotransmitter in certain brain regions may lead to some of the symptoms that we see in schizophrenia. By understanding something about neurons and neurotransmitter substances we can understand something about neurological and behavioral disorders. We can also understand how some drugs work that affect behavior. I’m going to talk about the impact of some drugs that are used to treat psychiatric and neurological disorders. I want you to remember something. When you take a drug, you generally take it orally, that is, you swallow a pill. However, when taken orally, a medication goes to the places you want it to go to have the effect you’re looking for, and it also goes to places where you don’t want it, causing side effects. For example, let’s say that you have a lung infection and so you take an antibiotic to treat it. That antibiotic goes through your bloodstream and hopefully kills the infection in your lungs. At the same time, it may go into your digestive track and kill some bacteria in your gut that are actually pretty useful. Sometimes people get stomach and digestive problems as a side-effect when they are taking antibiotics. Here is another example. Antipsychotic drugs have been used to treat schizophrenia. Most antipsychotic drugs are dopamine antagonists. What does this mean? This means that they reduce dopamine. They generally do this by blocking the postsynaptic neuron so that dopamine cannot have its effect to the same degree. By reducing dopamine, these antipsychotic drugs can have a powerful impact on behavior. They are frequently used in the treatment of schizophrenia to reduce the hallucinations and delusions of the disorder, and they do so pretty effectively. But there are side effects as well. This is because they also reduce dopamine in the part of brain called the nigra striatum, and one of the side effects of antipsychotic drugs is that they can produce Parkinson-like symptoms. If you look at videos of patients in psychiatric wards, you can see some move slowly, they don’t swing their arms (rather holding them tightly to their sides), and they appear quite still. These are all the Parkinson-like side effects; we say Parkinson-like because it doesn’t really lead to dopamine cell death, like you would see in Parkinson’s disease, and the symptoms go away if you stop the antipsychotic drug. It would be great if we could send the medication only where it’s needed and not to places where it’s not needed! This is one of the great challenges in current drug development efforts. neuroleptics L-Dopa: Now in the case of Parkinson’s disease, there is too little dopamine in the nigra striatum because the cells are dying. It would be good if we could give people dopamine to treat their Parkinson’s disease; however, dopamine is a large molecule and it does not cross what is called the blood-brain barrier (a system of microvascular cells that, among other things, protects our brain from toxins). But we can give people something called L-Dopa, which can cross the blood-brain barrier. L-Dopa is a chemical precursor to dopamine. When given to people with Parkinson’s disease, it helps them to synthesize dopamine in the brain, and it improves the symptoms of Parkinson’s disease. However, L-Dopa can have some side effects! Remember, it’s not just going to the nigra striatum; it also ends up in parts of the brain that may be implicated in schizophrenia. So, for some patients, a side effect of L-Dopa can be the development of hallucinations! Not a good side effect! SSRIs: Another class of drugs that has been developed to treat a range of psychiatric problems, including anxiety and depression, are the selective serotonin reuptake inhibitors or SSRIs. Serotonin is a neurotransmitter substance that is important in the regulation of mood; low levels of serotonin have been associated with depression (among other problems). So how do we think that the SSRIs work? Well, they do exactly what they say they do—inhibit the reuptake of serotonin from the synapse. When reuptake is inhibited, there is more serotonin available in the synapse to continue to have an impact. I think this can be confusing. Reuptake reduces the amount of serotonin that is available, and by reducing reuptake, increases the amount of serotonin available. It’s a bit of a double negative: by reducing the reducer, we increase serotonin. It is this blocking of reuptake that is thought to underlie the antidepressant effect of SSRIs. MAOIs: Let me tell you about another antidepressant medication. These medications are known as MAOIs, which stands for monoamine oxidase inhibitors. Norepinephrine, along with serotonin, is an important neurotransmitter that is widely distributed in the brain and seems to be strongly related to depressive disorders. Norepinephrine appears to be reduced in those with severe depression. So what is monoamine oxidase? Remember how I mentioned that one of the ways that we get rid of leftover neurotransmitter substances in the synapse is through degradation? Degradation occurs when enzymes come in and “clean up” the remaining neurotransmitter. Well monoamine oxidase is one of those enzymes, and it specifically “cleans up” norepinephrine. A monoamine oxidase inhibitor or MAOI will reduce the activity of monoamine oxidase. Again, we have a double negative kind of situation: the MAOI reduces the thing that reduces the norepinephrine (that is the monoamine oxidase). The MAOIs can be very effective in the treatment of depression; however, they’re not used all that often. Why might this be? Well, people who are taking MAOIs have to be on a special diet low in tyramine, as the MAOIs make it hard to metabolize tyramine. Ingesting foods high in tyramine, for example red wine or aged cheese, can be deadly for those taking an MAOI. One thing to remember about depression is that it is associated with thoughts of suicide and sometimes suicidal behavior. The last thing a doctor wants to do is give the patient a potentially deadly medication. I hope these examples give you a sense of why it’s important to understand processes involved in neurotransmission. I’ve focused on a few very “practical” examples, but there many, many more, both basic and applied. More on Neurotransmitters It is important to note that there have been over 100 neurotransmitter substance already discovered in the human brain. Our brains are highly complex and some of these neurotransmitter substances interact in ways that are not fully understood. I do not expect you to remember all of the neurotransmitter substances, but I’d like to highlight a few and ask you to remember them: Acetylcholine (ACH)—How many of you have heard of Lou Gehrig’s disease or ALS? In this disease, acetylcholine neurons in the periphery of the body die. This neurotransmitter substance is also of great interest to those who study Alzheimer’s disease, where there are greatly reduced levels of acetylcholine in the brain. acetylcholine Serotonin (5HT)—I mentioned that serotonin seems to be involved in depression, but it also seems to be involved in the regulation of aggression and also in sleep. Dopamine (DA)—I’ve already noted its important role in experiences of pleasure, psychosis, and movement. Norepinephrine (NE)—Also involved in the regulation of mood, movement, and arousal. Focusing on Structure: The Nervous System Click on this image to see a larger view Source: LiveScience Now that we’ve talked about brain function, let’s focus on brain structure. We’ll be focusing on the nervous system at a more general level, specifically at the anatomical level. First, let’s talk about some general divisions of the nervous system. At its largest level, the nervous system can be divided into two parts: the central nervous system (the brain and the spinal cord) and the peripheral nervous system (all the nerves in the body EXCEPT the brain and spinal cord). The peripheral nervous system can be further divided into the skeletal system and the autonomic nervous system. The skeletal system is involved in voluntary movement. When I reach out my hand, I’m engaging my skeletal nervous system. The autonomic nervous system is involved in involuntary, self-regulation (respiration, functioning of internal organs, maintaining heart rate, etc.). The autonomic nervous system is divided into two subsystems. The sympathetic nervous system controls arousal. For example, when faced with threats we can either fight or flee, and our sympathetic nervous system prepares us to do either, as our heart rate and respiration increases, blood flows to the muscles, and we prepare to deal with the crisis. Think about being chased by a large predator! Your body has to be ready for that! The parasympathetic nervous system is activated in calming sorts of situations. Think about the period of time following Thanksgiving dinner when we sit down to watch the game or take a nap. Digestion takes place at this time and heart rate and respiration are slowed. Pathways from the peripheral nervous system lead to the spinal cord, which transmits messages up to the brain. However some messages never go on as far as the brain. We have reflexes that operate at the level of the spinal cord. Most of you have probably been to a doctor’s office and had the doctor tap on your knee with that little rubber hammer. Your leg pops up involuntarily—this is an example of a spinal reflex. Another example is when you touch a hot stove and instantly pull your hand back. Some of you may have had the experience where you pull your hand back quickly but you don’t experience the pain for a few seconds. Although a spinal reflex causes you to withdraw your hand, the experience of pain occurs in the brain. It takes time for the pain signal to make it to the brain where it is processed. It’s a good thing that you don’t have to wait to feel the pain to pull your hand away—otherwise you would have been burned quite a bit worse than you were already. Source: Magic Spangle Studios: 3D Medical Animation—Central Nervous System Focus: The Central Nervous System So let’s focus on the central nervous system. As noted before, the spinal cord goes up into the brain. We can think of the brain itself as composed of three concentric areas: the central core, the limbic system, and the cerebrum or cerebral hemispheres. I’d like to discuss briefly some of the important structures in each of these areas. Let’s now focus on the central core. The central core is also known as the hindbrain and as the “old reptilian brain.” We refer to it as the old reptilian brain because, evolutionarily speaking, it is old, and it is shared by our distant reptile cousins. The central core helps regulate our internal processes (respiration, heart rate, etc.), allows us movement, and governs our level of arousal. These are all things that our distant reptile cousins are also able to do. Let me focus on several structures within the central core that I’d like you to remember: Source: SciShow—No, You Don't Have a "Reptilian Brain" Medulla Oblongata—This area is located at the top of the spinal column and regulates breathing and some reflexes involved in posture as well. It is at this point that many axons cross over so that control of the right side of the body is on the left side of the brain and control of the left side of the body is on the right side of the brain. Damage to the medulla oblongata, which can happen in severe car accidents, often leads to death. Cerebellum—This area helps coordinate movement. Damage to the cerebellum can lead to jerky and uncoordinated movement. Please make sure to distinguish between the cerebellum and the cerebrum as these are quite different. Reticular Formation—A structure along the central core, the reticular formation is involved in our level of activation and alertness. When you wake up in the morning your reticular formation fires up. Pons—Along with the cerebellum, the pons helps coordinate movement on both sides of the body. So, for example, when you are walking, as your left leg swings forward your right arm does as well and vice versa; this coordination is due to the hard work of the pons. The next concentric circle is what we call the limbic system. The limbic system is also known as the midbrain and the “old mammalian brain.” We think of the limbic system as the seat of emotion (very important). Other mammals also appear to experience emotion. If you think about your dog, your cat, or other mammals, you know that they can experience intense emotional reactions; reptiles, who lack the limbic system, don’t appear to experience emotions. Let’s face it, your pet lizard will never love you, but your dog will! Let me focus on several structures within the midbrain or limbic system that I’d like you to remember: limbic system Source: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436 Thalamus—The thalamus is a major relay station. Information comes up from the peripheral nerves up the spinal cord into your thalamus and is sent out to various regions of the cerebral cortex. Information comes in from the cerebral cortex and goes through the thalamus and is sent out down the spinal cord and into the body. Hypothalamus—This rather small structure is responsible for homeostasis. Homeostasis is the balance that our bodies maintain—relatively stable blood pressure, temperature, glucose concentrations, etc. Hippocampus—This horseshoe-shaped structure is essential in the formation of particular types of memories. We will talk about it much more in the Memory section. The top concentric circle is known as the cerebrum or cerebral hemispheres. This is the highly convoluted cauliflower-looking structure surrounding the limbic system. This section appears to be relatively larger in humans than in other species. And we tend to think of those creatures with large cerebral hemispheres (as a percentage of total brain area) as being “smarter.” So, for example, dolphins and whales have large cerebral hemispheres, as do elephants. The outer layer of the cerebral cortex is composed of many cell bodies and we refer to this as the “gray matter.” Underneath the gray matter is what we call the “white matter,” which is composed of many myelinated axons. Let me focus on several divisions within the cerebral hemispheres that I’d like you to remember. Each side of the brain is divided into four lobes. cerebrumSource:By vectorized by Jkwchui [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons, CC BY-SA 4.0, At the back of your head is what is known as the occipital lobe. The lobe is essential in processing visual information. Damage to the area can lead to problems with vision; we will talk a lot more about this later in the module. On the size of the head near the ears is the temporal lobe. As you might imagine, just by location the temporal lobes are involved in hearing, but they are also involved in some aspects of vision. Damage to the temporal lobes can lead to difficulties in understanding and using language. Up at the top of your head is what is known as the parietal lobe. The parietal lobe is involved in the processing of what we call somatosensory information—touch, pressure, temperature. At the front of the parietal lobe is the sensory strip where this somatosensory information is primarily processed. I’d like you to take a look at this very odd image. This is known as the sensory homunculus. I don’t need for you to be able to identify this exactly or know all the details by any means, but I want you to understand what it illustrates. What this sensory homunculus is showing you is the amount of cortex in the sensory strip that is required for the processing of somatosensory information from different parts of the body. You will note that areas of the body that are more sensitive (to touch, pressure, heat, etc.) take up a greater area of cortex. An area like your lower back, which is not particularly sensitive, has a small amount of room allocated; whereas, an area like your tongue or lips, which are very sensitive, have more space allocated. sensory homunculus At the front of your head or skull is what is known as your frontal lobe. At the very back of the frontal lobe is an area called the motor strip. The motor strip is directly across from the sensory strip in the parietal lobe. And there’s a lot of “crosstalk” between the sensory and motor strips. For example, if you feel an itchy sensation on the side of your nose you may scrunch up that area to relieve that sensation. So sensory information comes in to the sensory strip and we respond with motor action (based in the motor strip). Just as I showed you a sensory homunculus, there’s also a motor homunculus. As with the sensory homunculus, more space is allocated to areas of the body that have greater dexterity. So, for example, very little space on the motor strip is allocated for your knee. After all, you can’t do that much with your knee. On the other hand, your fingers, thumb, and tongue have a lot of space—they are particularly dexterous. But there’s a lot more going on in the frontal lobe! This is the area that I noted earlier was damaged when the tamping iron shot through the skull of Phineas Gage. The frontal lobes are intimately involved in reasoning, planning, higher-level thought, abstract thinking, and control of emotions and social behavior. Interestingly, across development, the frontal lobes develop late, which explains why children aren’t very good at planning, reasoning, abstract thinking, controlling their emotion, or having more complex ideas. When people have frontal lobe injuries, they often have difficulties with emotional control and appropriate behavior. The two halves of the brain are roughly symmetrical and are connected by the corpus callosum. The corpus callosum is composed primarily of myelinated axons that carry large amounts of information between the two sides of the brain. I would encourage you to read in your textbook about split-brain procedures, where the corpus callosum is severed, so that you can understand its impact. What follows is a fascinating introduction to the regions of the brain that is conducted by Suzanne Stensaas, PhD, Department of Pathology, School of Medicine, University of Utah. While it is 13 minutes long, you will be looking at an actual human brain, and will be able to observe very clearly many of the previously mentioned brain structures, including the corpus callosum. Watching this video will help you remember the material in this section. Neuroanatomy Video Lab - Brain Dissections Do You Remember? Sensation and Perception Introduction Today we continue our exploration of the biology of behavior. Our topic is sensation and perception. The question addressed by the study of sensation and perception is really “how do we come to know the world?” There’s a lot of information out there in our world and we take it in through our senses: hearing, taste, touch, vision, smell. How is it that these processes work? moji of Dr. Tompson with the words,Perceptual systems evolve to enable us to adapt to a changing world I’m going to provide you a broad overview of sensation and perception, but I’m going to focus on visual perception. This focus is because researchers know more about visual perception than some of our other senses and because, as a species, we rely so heavily on visual perception to know our world. Sensation and Perception: Information Processing in the Brain Sensation and perception are almost always studied together because they almost always go together. However, we can also separate them in our discussion. When we speak of sensation, we are talking about the process of detecting a physical stimulus, such as light, sound, heat, scent, or pressure. When we speak of perception, we are talking about the process of integrating, organizing, and interpreting sensations. Without perception we wouldn’t really know what those sensations mean. When we talk about sensation, what is it that we are responding to? Each of our sensory systems have evolved to be sensitive to particular stimulation in our environment. In visual sensation, we are responding to wavelengths of light. In auditory (hearing) sensation, we are responding to physical vibrations in the air. In olfactory (smell) sensation, we are responding to airborne chemical molecules. In gustatory (taste) sensation, we are responding to dissolvable chemicals in the mouth. Our sensory systems have evolved to be sensitive to particular information out there in our world and to enhance our survival. Basic Principles and Terms Let’s focus on some basic principles and terms in the study of sensation: Stimulus – The thing out there that we are trying to detect with our sensory organs: an image, a sound, an odor, etc. Sensory receptors — Specialized cells unique to each sense organ that respond to a particular form of sensory stimulation (a stimulus). What do we know about these receptors? Well, first of all, the simulation needs to be a certain level for us to detect it at all! Sensory thresholds define the level at which a stimulus is strong enough for our sensory receptors to detect it. The absolute threshold is the smallest possible strength of the stimulus that our sensory receptors can detect about half the time. Absolute thresholds include for smell, one drop of perfume throughout a three-bedroom apartment; for hearing, the tick of a watch at 20 feet; for vision, in the range of 54 to 148 photons (depending on conditions). These are examples, but I do not expect you to remember them on an exam! The difference threshold is the smallest possible difference between two stimuli that can be detected half the time. We also call this the just noticeable difference (jnd). The difference threshold is how much we need to change the stimulus for you to know that it’s stronger. How much brighter does the room need to be before you notice a change in brightness? How much louder does your roommate need to speak before you notice? Weber’s law indicates that the size of this difference threshold (the jnd) will depend on the strength of the original stimulus. The stronger the original stimulus, the larger the difference needs to be to get noticed; and a ratio helps us understand this. For example, imagine that you are listening to some music, some soft soothing classical music (at 30 dB) as you drink your tea early on a Saturday morning. You want the music to be a little bit louder, so you turn the dial ever so slightly and notice that the music is comfortably louder and that this took only 3 dB. So in this case the ratio is 30:3. On the other hand, imagine that you are at a concert, a heavy metal concert with some friends. Maybe you wanted to go, maybe you didn’t want to go, that’s up to you. But the music is pumping, amplified to 120 dB. Let’s say the band feels that the music needs to be just a little bit louder (as if your ears aren’t already bleeding). Given what we know from the previous example—that for every 30 dB you need to increase 3 dB—how much does the band need to increase the volume of this heavy metal music before you would notice a difference? Well, if you said 12 dB, you would be right! It adheres to Weber’s law—3 dB for every 30 dB. Again, this is an example to illustrate Weber’s law. Transduction—This is a process in which physical energy (like light waves) is converted into a coded neural signal that our nervous system can understand and interpret. Sensory adaptation—This is a decline in responding to a constant stimulus. What does this mean? Let’s think of an example. Imagine yourself just having jumped into a freezing cold swimming pool. You feel a desire to levitate out of this icy water, and you may feel a prickling pain. But the longer you stay in that cold water, the less you notice it, and you may begin to feel perfectly comfortable. You have just experienced sensory adaptation. Let’s think of another example. Have you ever moved into a new apartment? Maybe there was an irritating sound next door that kept you awake for a while on the first night (perhaps the sound of an air-conditioner humming), but soon you cease to notice it at all and begin to sleep just fine. You’ve experienced sensory adaptation. Here’s one more example. How many of you have ever walked into another person’s home and been overwhelmed by the smell of what’s cooking (let’s say it’s garlic), but after a while you cease to notice it? The next person who comes in and says, “Wow, what a smell!”, and you respond, “What smell?”. You’ve experienced sensory adaptation. This helps you adapt! There are so many things to notice in our sensory world, and once we have perceived and adjusted to them our sensory systems need to move on to other things. Focus: The Visual System As a species, human beings are particularly dependent on vision to help us learn about the world around us. This is not to say we can’t do without vision, as many people who are visually impaired or blind function quite well. But for most with normal vision, we become highly reliant upon it. How is it that we see? First, wavelengths of light are the type of energy to which our visual receptors respond. I’d like you to take a look at this illustration of the electromagnetic spectrum. It’s interesting in that there is a HUGE amount of potential electromagnetic information out there in the world; the visible spectrum (what our visual receptors can detect) is only a small slice. We cannot see radiowaves or UV radiation or microwaves or gamma rays! There’s a lot happening out there that we don’t have access to. In fact, astrophysicists use very specialized equipment to increase the amount of the electromagnetic spectrum that they can “see.” That little slice of visible light provides us with a huge amount of information about our world. Electromagnetic SpectrumElectromagnetic Spectrum Vision involves a complex chain of events. Light is reflected from an object out there in the world, enters the eye, and passes through a number of structures: The first structure is your cornea, which is the clear membrane covering the visible part of the eye; it helps to gather and direct the incoming light. Interestingly, eye surgery often involves the shaping of the cornea using lasers. The second is your pupil, which is the opening in the middle of the eye that changes size to let in different amounts of light. It is surrounded by the iris, which is a muscle which controls how large the pupil is; the iris is that colored part of the eye. Here’s an interesting bit of information (which, while not on the exam, may help you in your personal life!). When you see something you like, your pupils get bigger! So if you see someone you find attractive, your pupils widen! Maybe you are just trying to get a fuller view! Also interesting…we look more attractive when our pupils are larger! Studies have been done using photographs of people and having others rate their attractiveness; photographs that had been touched up to make the pupils slightly larger were judged more attractive. Now remember that your pupils expand to take in more light in dark situations. My theory is that candlelight dinners are particularly romantic for this reason: You are sitting across from your mate in the candlelight and both of you have huge pupils! You think, “Wow, you are amazingly attractive, your pupils are so large!” (Actually, you aren’t even consciously aware of why!) The third is the lens. The lens is a transparent structure that focuses the light right onto the next, very important, structure. That final structure is the retina—this is where the sensory receptors for light reside. These receptors are known as the rods and cones. Here are a few things to know: The rods (over 100 million of them) are very sensitive to light and to movement but don’t do so well with color. The rods really fire up in low light situations, but it takes time. If you go outside on a dark night for a walk, you may not see well at first but over time, as your rods get going, you begin to see much more clearly. It takes about 30 minutes for these rods to really get going and hit their maximum sensitivity. The cones (about 6 million) are sensitive to color and contribute to visual acuity (they help us to see small details clearly). Densities of rods and cones in Human retina Now this next slide is interesting. It shows the distribution of rods and cones across the retina. Along the bottom of the figure (the x-axis) is the location on the retina, and along the side of the figure (the y-axis) is the density of rods (in black) and cones (in red). You will notice that at the periphery of your eye (edges of your retina) you have lots of rods, but in the middle there are mostly cones. The area in the middle is known as the fovea, and it is the most sensitive to small details. When you want to view an object carefully and clearly you look at it directly so that the image falls on the fovea. Let’s say you want to look at your friend’s new engagement ring—you look directly at it, the image falls on the fovea, and you are able to see all the details in the setting and all the tiny stones around the edge. You don’t look at it sideways! On the other hand, if you want to look for a very faint light, your rods are better at this. On a dark night when you are stargazing and want to see a very faint distant star or planet, you are better off looking just to the side of where that star or planet should be. Then the image falls on the rods, which are more sensitive to faint light. Different receptors may be particularly sensitive to different colors of light and different angles and lines. Information from the rods and cones is then transmitted to bipolar cells and ganglion cells. These cells then form the optic nerve, which is a bundle of axons that transmits the information to the back of your brain—an area known as the occipital lobe—where it is processed. Just for fun, below are two different images that depict rods and cones and their distribution in the retina. Source: Scientificanimations OpenStax College, via Wikimedia Commons Visual problems, including blindness, can be due to many factors. First, you may have damage to the structures of the eye—the cornea or lens—for example, following an accident. Second, you may have damage to the rods and cones in the retina, for example, due to macular degeneration (deterioration of cells at the center of the retina). Third, there may be problems with the optic nerve, for example, as a result of degeneration of myelin due to multiple sclerosis (MS). Fourth, you may have damage to your occipital lobe, for example, as a result of a stroke. Vision is a complex change of events, and problems can happen at many levels. Once the information reaches the occipital lobes, an increasingly complex set of events takes place. We put the information together, add it to what we already know about the world, and form conclusions about what it is that we are seeing. How Do We See Color? Another important part of visual perception is perception of color. We seem to be pretty good at being able to judge colors. So how do we do this? Any object’s color is a function of what wavelengths of light that object reflects. So, in reality, color is just our perception of different wavelengths. Let’s talk more about what the perceptual experience of color really is, as it involves three different properties. The first property is what we call hue, and it is a property of wavelengths of light. We see different wavelengths in different ways and, based on hue alone, you can see about 120 different colors. The second property is what we call saturation, and this corresponds to the purity of the wave of light, that is the degree to which it is or is not influenced by grays. The third property of color is known as brightness, which corresponds to the amplitude of the light wave. All these properties combine to allow us to see color well. So how is it that we see color? Well there are two theories of color vision. Let’s talk about each. First, the trichromatic theory of color vision states that our perception of color is due to the fact that certain cones in the retina are sensitive to either red light (long wavelengths), green light (medium wavelengths), or blue light (short wavelengths). When you see a color reflected off an object, some of each of these cones will be stimulated, and the total combination will lead to your perception of the color. This particular theory has been helpful in understanding colorblindness. In colorblindness, an individual may be missing cones for either the red, green, or blue wavelengths. And, in fact, red blindness and green blindness are fairly common forms of color blindness. Second, the opponent process theory of color vision suggests that our perception of color may be due to opposing pairs of color receptors, including blue/yellow, red/green, and black/white. When one member of the color pair is stimulated, the other is suppressed. The opponent process theory of color vision is pretty good at explaining the afterimage. Look at this video to have a demonstration of the afterimage. You need to look at the original image very closely and intensely—focus your eyes at the center of the page—and when it is withdrawn you will see the negative afterimage. Color Flag Afterimage What has happened here is that you’ve stimulated one member of the color pair, and when that color is withdrawn there is a surge in the opposing color. So you go from seeing a black, green, and yellow flag to seeing one that is red, white and blue. It has been determined that both the trichromatic theory and the opponent process theory may both be true, just at different levels of visual processing. So, we’ve focused on processes in sensation…now let’s move to the next piece of the puzzle: Perception The visual systems allow us to collect a lot of information from out there in the environment, and now we need to be able to process that information in a way that we can then make sense of it. We have to figure out what it all means! We learn over time, through experience, how to interpret this information. Our visual systems allow us to make sense of the world and to answer particular questions about the world around us. What are some of the major questions our visual system can answer? Remember: your visual system has evolved over millennia to enhance survival. Imagine that you, an early human, are standing out on the plains of Africa. You see a creature in the distance. What important questions do your visual systems need to answer about this potential information? Three are particularly important: How far away is the object? Where is it going? What is it? We'll look at each of these questions more closely on the next pages. Depth Perception First, how far away is the object? We use a number of important pieces of information to answer questions about an object’s distance. Take a look at this figure, as it details information that we use to tell us about distance. Two sets of factors provide information about distance. The first set of factors available to us are called monocular factors. Mono=one; ocular=eye. We could get information about distance even if we only had one eye. The second set of factors available to us are called binocular factors. Bi=2; ocular=eye. The fact that we have two eyes also helps us judge distance. Let’s focus first on monocular factors. Among the monocular factors are those at play when objects are moving and those at play when they are either still or moving. Among the factors we use to judge distance without movement are those known as pictoral cues. We call them pictoral cues because they are also used by artists to give a sense of depth to paintings that would otherwise seem like a flat canvas. What are the these pictoral cues? Relative Size. When we look far away and see two people coming toward us and one is very small and the other is much larger, we know that the larger one is likely much closer. We don’t assume, as this would be quite incorrect, that the larger one is simply an enormous person and the smaller one is a very tiny person. We have all learned that relative size tells us something about distance. Overlap or Interposition. When we look out at a beautiful rustic scene and see that a barn is partly obscured by a large maple tree, we recognize that the maple tree is between us and the barn. We don’t assume that it’s a weird barn with a maple tree in the middle of it. We’ve learned that when one object partly obscures another, that obscuring object is between us and the other object, is overlapping the other object, or is an interposition between us and the other object. Aerial Perspective. This cue is at play for very long distances. When we’re looking at distant mountains, we can judge their relative distance (compared to other mountains) by how obscured they are by the atmosphere. We know that the ones that are more blurred by the atmosphere are further away than the ones that are less blurred. We have learned that the amount of blurring from the atmosphere (aerial perspective) gives us information about the distance. Texture Gradient. If you’re standing on a cobblestone road, you can look out in the distance along the road and see that the cobblestones up close are easy to see as individual objects. As you look further out, the cobblestones begin to gradually become less distinct and eventually appear only as splotches of different colors. Similarly, if you look out over a crowd, the people close to you appear as individuals, but the further you look the less distinct they are, and eventually they just become a sea of different colors. You’ve learned to interpret this gradual change (texture gradient) as an indicator of distance. Linear Perspective. Let’s say you are standing on a railroad track that goes off in a straight line into the distance (don’t actually do this, it’s not safe; let’s keep it as a thought experiment). If the track is very straight, the two rails will appear as two lines that get closer and closer together the further away they are. Going back to the idea of pictorial cues, you can see how artists used this linear perspective to give a three-dimensional idea when they were, say, painting a town with streets that go off into the distance. Monocular Cues: Adjusting to Depth Perception Problems In addition to the information provided by these pictorial cues, we also use information from the amount of change in our eye muscles required to keep the object in focus. This is called accommodation. Our brain has learned the meaning of particular amounts of accommodation as representing particular distance. When an object is moving, we also use something called motion parallax—closer objects move faster and more distant objects move more slowly. Think of yourself on a train and you’re looking out the window. The objects close to you, including stations, trees, grasses and other objects, whip by very quickly. Faraway objects, like mountains, move very slowly. We use this information to give us a sense of distance. I think it’s important to remember that we learn to use this information and interpret its meaning. So those are the monocular factors. But most of us have two eyes and are able to take advantage of this fact when judging distance. Strategies that use both our eyes together to glean information about distance are referred to as binocular factors. So what are these binocular factors? First, we use retinal disparity to give us a three-dimensional image of the world. You get slightly different images from each of your eyes. If you close one eye you see one image, and if you close the other eye you get a slightly different image. Your brain puts these two images together and produces a three-dimensional perspective on the world. I don’t know if any of you have ever traveled to an international city and visited a gift shop. I remember going to one in Paris and getting something called a stereograph. The stereograph looks like a set of binoculars, but it has slides of different images enclosed in it. One image goes to the right eye and a different one goes to the left eye. It fools your brain by giving different information to each eye and you perceive a three-dimensional object. I remember being in Paris and getting a stereograph with an image of the Arc de Triomphe. Second, we use convergence to give us information about distance. Put your finger up about a foot from your eyes and move it slowly toward your face. You will notice that your eyes each move inward to keep the object in focus. You’re crossing your eyes slightly and that information—the amount of convergence—is used by the brain to give you a sense of how far away the object is. So you are able to use a lot of information to answer this very basic question: “How far away is it?” Motion Perception Where is it going? So, after you know how far away the object is, you might want some additional information. What’s the next question you want to answer? That question is, “Where is it going?” I think you’d want to know whether the object was moving away from you across your line of sight, or toward you. Clearly, information on this might enhance your survival! So here are some assumptions we make in motion perception: We interpret motion across the retina as indicating movement “out there.” This information helps us in determining where an object is going. Is it moving towards us, away from us, across our line of vision? Is it getting larger? As the object moves across the retina, we have to adjust our eye movement to be able to keep that object in focus. And our brain is able to use information on the microfine adjustments our eyes make to tell if it is getting closer or further away. We also compare the moving object to the stationary background. We make the assumption that objects move and backgrounds stay stationary. This is generally a pretty good assumption in most situations. Sometimes it is easiest to illustrate these factors when we consider illusions of motion—these are times when our visual systems are fooled by the assumptions we make about the nature of moving objects. There are two that are pretty interesting. Induced motion. We assume that the background is stationary and the object moves, but this isn’t always true. The Moon illusion is an example of this. When you look up at the Moon in the middle of the sky on a windy night with lots of clouds, it seems that the Moon is racing through the clouds, even though it really is the clouds that are racing past. It will also give you an odd sort-of dizzy feeling. Now I suppose one could argue (especially if you study astrophysics) that the Moon and Earth are certainly always moving, but I would respond that this certainly does not explain the induced motion illusion here—in a much more immediate and close-at-hand way the clouds are what is really moving.Let’s think of another example…how many of you have been driving and maybe eased up too much on the brake? Your car starts to move but you perceive it as others around you moving! You are making the assumption that you in your car (the background) are stationary and the other car (the objects) is in motion. Oops!! Stroboscopic motion. Here’s another interesting example of when our visual systems can fool us. Let’s say I lined up 12 LED lights in a row. I lit up the first one, and just as I turned it off I lit up the next one, and just as I turned that one off I lit up the next one, and just as I turned that one off I lit up the next one, and so on. What would you see? You would perceive it as the light jumping from one spot to the next spot. In other words, you would see motion where there actually was none! The light moves across the retina, and we interpret this as motion. When we see light changing in this way we can assume erroneously that there is actual movement. Let me give you another example of this phenomenon in play. How many of you have ever seen moving neon signs? I remember being in Las Vegas and seeing one of a coffeepot “pouring” coffee into little neon cup. There was a stream of lights from the spout of the pot into the cup. As one light went off the next went on, and so on. It appeared as if the drops of coffee were actually pouring into the cup. Let’s consider another very interesting example. Cartoons use stroboscopic motion as a means of allowing us to see motion from still objects. In a cartoon, a succession of images of the cartoon character are rapidly flashed in front of us. Each image is slightly changed in every exposure, so it casts a slightly different image onto the retina. These gradual changes are interpreted by your visual systems as movement even though it’s just that you are seeing that changed object in quick succession. Alright? So the sad truth is that Bugs Bunny can’t actually move. Motion Perception Clearly, the assumptions we make about the nature of the world, based on our experience with it, allow us to fairly accurately judge the distance of objects, to determine whether an object is moving toward us or away from us, and so on. So we are collecting info but we are also making judgments based on our previous experiences. Although we can be fooled by the assumptions we make, we are, happily, pretty accurate most of the time. I think it is very important to recognize that these processes are automated and generally happen out of our awareness. Shape Perception What is it? So, what’s the next question you’d want to ask? Remember that you, an early human, are standing out there on the plains of Africa and see a creature in the distance. You’ve determined that the creature is far away now but is moving towards you. Now the next big question, and perhaps the most important question, would be: “WHAT IS IT?” If it is a meerkat (a harmless and cute little critter), you don’t need to worry, but if it is a lion (a large and fast predator), you perhaps want to start worrying and potentially plotting your escape route. Shape perception is basically answering that question: What is that thing out there? You have receptors in your retinas that are sensitive to all sorts of small details—lines, edges, angles, etc. It seems like a lot of information! How do you pull all of that together into something that makes sense? That’s a very tricky task. Your brain takes all this information and makes a perceptual hypothesis about what that object is. This hypothesis is based on all the information you’ve collected about angles and lines and adds it to what you already know and have experienced in the world. It’s amazing how good we are at all of this. All day every day we are responding to objects out there; we are collecting data, putting it together, and making hypotheses about the nature of the objects. Now one thing we do know is that shape is the primary determinant for identifying an object. Infants, children, and adults name new objects according to their shape (not color, not size). When we categorize items, we do so according to shape. This is referred to as shape bias. Now, I want to distinguish between bottom-up processing and top down processing. Bottom-up processing is recognizing an object based on its component parts. Bottom-up processing is built on our collection of the smallest pieces of information. Top-down processing is when you take all those little pieces and you make a perceptional hypothesis. As a simple example of top-down processing, you say “It has a back, a seat, legs—it must be a chair!” You are taking all that information, putting it together with all that you know about chairs and other objects, and making that perceptual hypothesis. Top-down processing is really built on higher cognitive processing. Now I am giving you a very concrete example; in reality, when you perceive the environment through your retinas you are getting a lot of very minute information, and you are putting it together to say, “That must be a so-and-so.” Again, you make that perceptual hypothesis. In this processing, bottom-up and top-down occur almost simultaneously. You collect all this information and you make a hypothesis on what it is, and you are pretty good at doing that. This is an unconscious activity that you do all day long. You see things and you identify them, and you are making your best guess. Sometimes you are wrong, but most of the time you are right. Sensation and Perception—Top-Down and Bottom-Up Processing Making Sense of a Complex Visual World: Gestalt Psychology Now one of the things we have to do when we are out there in the world is we have to try to make sense of very complex stimuli. When you look out onto a scene, perhaps while walking down a street, you are seeing a very complex set of visual inputs, right? One of the first things you do is to start pulling that scene apart—into its component parts. What pieces go together and what pieces are separate? Part of this process is determining the figure-ground relationship—the perceptual process of separating the main elements from the background. As you walk through the museum, you see all of the beautiful things around you. You may see an amazing painting—you think, “Ah, this is a picture of vase!” Yes, the vase is surrounded by flowers and fruit, but you are separating the elements—the vase is the figure the rest is background. You are looking out at a lovely scene as you hike on a warm spring day. You see a huge oak tree with a nest in it; you think, “Ah! Look at this amazing tree with a bird’s nest. (I wonder if there are some eggs in it?)” Yes, the oak is surrounded by saplings, old leaves, other small trees, and shrubbery. But the oak tree is the figure, everything else is the background. You engage in a process where you separate the central object, the main element, from its background. In this figure-ground process, we also “parse” a complex visual input (scene) to try to determine which elements go together. Gestalt psychologists studied the laws that governed perception and were very interested in how we parse (separate into pieces) a complex environment. How do we go about pulling apart a complex scene so that we can understand the pieces that do go together? What are the laws that govern perception? Gestalt means “Whole-Form.” Gestalt Principles Here are some of the “laws” that govern how we parse the scene. The first is based on similarity; we tend to see things that are similar as going together. Look at the example to the right. Most of us would say that there are two lines—each composed of objects that are similar in shape and color; even though the lines are overlapping we see them as distinct from one another and each forming a whole. As another example, let’s say you are walking in the woods and you see leaves that are shaped similarly to one another—maybe they are maple leaves. You tend to say, “Ah! That’s all part of this one tree” because the leaves are similar. Another law governing parsing is closure; we tend to close, or complete, objects that appear to be unclosed or incomplete. Take an example that follows. rectangles You see these squares? Now most of us wouldn’t say, “Wow, that’s a blue square and a gold and red square with little chunks cut out of the corners!” When you are perceiving objects, you close each of them; you say: “Ah, those are three squares—blue, gold, and red—that are overlapping.” So you closed two of the three objects so that you see them as whole, full-formed objects. Another law governing parsing is that of good continuation. We tend to see objects as continuous. So if you are looking at a path going out away from you, and it’s partially covered by leaves, you are not going to say, “Oh, that’s a path with a huge gap in it.” You would say, “The path is continuous—t’s partially covered, but it is continuous.” That’s this idea of good continuation. I think one of the things that is interesting about these processes is that we can make mistakes and miss things. We all make assumptions in our perceptual process, and most of the time we are right, and that’s why we keep doing it. But sometimes we are wrong, and good continuation is an interesting example of where you can be wrong. So, how many of you know what camouflage is? I’m guessing most of you. We say that an animal can camouflage itself when it can disguise its presence and blend into the environment. For example, a praying mantis or other insect is very hard to see because it blends in with the texture and/or color of objects around it. When you are looking at a leaf and it has a stem, you don’t necessarily see that the praying mantis is laying across that leaf, because you don’t expect to see it there; it’s green, and it continues in the same color and direction of the leaf. We tend to not notice it because of our assumption of good continuation—we are making an assumption here that things continue in an expected way, and we parse the insect with the leaf, when actually it is not the case; indeed it is a separate object. There is an insect here, interrupting the texture, and yet we see it as continuous and miss that camouflaged insect altogether. Proximity is another law that governs parsing. We tend to group things that are close to one another as one object and we tend to group the ones that are a little further away as a separate group. Take a look at the example that follows. shapes depcting proximity So here in this visual example you probably see three groupings of these green hexagonal shapes, and you see them as separate groupings because they are farther from one another, and yet the three are close to one another. That’s part of that natural separating process—what you are doing is that you are pulling things apart and figuring out what goes with what. Now imagine you are back in the woods and see maple leaves again. You would tend to see one group (all close together) as belonging to one tree; a group of maple leaves further away (all close together) would be perceived as belonging to a different tree. So, you are using these “laws”—similarity, closure, good continuation, and proximity—to govern how you pull the world apart and put it back together as you attempt to make visual sense of a complex environment. Now, we’re making these perceptual hypotheses all day long! There is one central law that is above all others. Known as the law of simplicity, or Pragnanz (in German), it is the governing principle of the Gestalt psychology. It states that when more than one organization is possible, the one that you choose will be the one that produces the best, simplest, and most stable shape. So you could interpret the visual input in a number of ways, but you choose the one that is the best, simplest, and most stable. And I think this really goes back to the idea that in our daily lives we are all, in some ways, scientists. Every day of our lives we go around looking for information, collecting data, and making hypotheses about what those things are out there in the world, and most of the time we are pretty good scientists! How many of you know what Occam’s razor (or the law of parsimony) is? It’s the idea in science that the simplest explanation is probably best. So what that basically means in science is that we don’t choose the most complex hypothesis or theory, we want one that explains the phenomenon well, accounts for all the different aspects of it, but that’s fairly simple. We want it to be straightforward, and that’s what we do every day as perceptual scientists! We have lots of info coming in and we choose the simplest, most stable, best hypotheses to explain the phenomenon that we see. So that’s basically the idea of the law of simplicity, or Pragnanz—the governing principle of Gestalt psychology. cups or faces graphic Source: Bryan Derksen, via Wikimedia Commons Look at this. What do you see? How many of you see a vase? How many of you see two faces looking at each other? I think if you screw your eyes up a little bit, you can go back and forth and see both. This is what you call an ambiguous figure. This is the very unusual instance where you become aware of your processing of the figure-ground relationship. The idea here is that where it’s not so clear what the figure is and it’s not so clear what the ground is, you can kind of go back and forth in thinking about how you are going to interpret that figure-ground relationship. This is a situation where that simplest, most stable, best form isn’t so obvious (it’s ambiguous). However, we don’t often encounter these things. The Importance of Context and Prior Knowledge: Bottom-Up and Top-Down Processing Let’s talk about bottom-up and top-down processing again. Please go now to the site called OpenPSYC to read the material there. Be sure to watch the short (~ two minutes) video called Phonemic Restoration Demo. It’s interesting to think about how we rely on context to help us to interpret the world. Selective attention I want you all to think about—just do this little exercise for a minute—and think about a penny. A copper penny. What’s on a copper penny? Whose face? Lincoln. Which way is he facing? How many of you are not sure? I am not sure either. And what does it say on the copper penny? Can you remember? One of the things this illustrates is that we perceive the world in ways that are useful to us. How many of us need to know all the details of the copper penny? If you are a collector of coins, sure, you notice all those kinds of details, but most of us probably don’t. It’s good enough that it is the copper one, it’s a different color than the rest of the American money, so we know it’s a penny. And it has a certain kind of size—it’s bigger than a dime but smaller than a nickel. Most of us don’t notice the other details because we don’t need to. So in some ways, what you notice in the environment is also governed by what we call selective attention. You are attending to certain aspects of the world that are important to you and meaningful and helpful, but you may not be attending to the small details of things that you see every day. You are seeing the world in context and you are looking for certain things—things that are meaningful and can help you navigate the world. Automated processing top dpwn and automatice processing reading example How many of you can read this? Probably many, if not most, of you. It’s strange that any of us can read this, but many can! What the authors of this have done here is keep the first letter and the last letter of words and they flipped all the letters in between. How can anyone still read it? Part of what’s happening is that reading is highly automated (you have been reading since you were what? 5? 6?). You have been reading a long time, and you almost cannot NOT read—if you see a sign by the side of the road or on the subway or any other place, you are going to read it. So what’s happening here is that you have this very automated process; you have learned to recognize words, not by looking at every single letter, but by taking in the whole gestalt. Some folks have a harder time with automating this language recognition—folks with dyslexia or folks less familiar with English may have more trouble reading this. Most of you can do that fairly readily, and I think this is such a good illustration of top-down processing. If we didn’t read the world in this automated kind of way, imagine how hard it would be? For those with dyslexia, learning to read often takes a lot more work; they may learn to read automatically using a different approach. Automated processes allow you to go about the process of perception in a very efficient way. Perceptual Constancy Now you may think to yourself, “Isn’t it kind of weird that we have this constantly shifting world, and yet we are able to maintain some sense of consistency? How is it that even when objects change shape as they move we are able to see things in the same sort of way?” This is known as perceptual constancy. That is this idea that we maintain consistency in an ever-shifting world. So you are likely to recognize your friend even if you see them in a new place (like the grocery store), or even if next week they wear their hair differently. You’d recognize them if they put on a coat or wore a hat. Even though the light is different, the clothes are different, the time of day is different, so many things are different, we still maintain our ability to recognize. Some aspects of perceptual constancy include: Color constancy. You see color the same way even if you walk through a shadow; your green sweatshirt would still be perceived as the same color on a dark rainy day as on a sunny one. You still perceive that green even though its appearance has actually changed quite a bit. In these two pictures the lighting is very different, but you still see the oranges as orange, the banana as yellow, and so on. Brain Games—Seeing Color and Color Constancy Shape constancy. Shapes are shifting all the time. When I move from one side of the room to the other, my shape changes, and when I move around, my shape changes. Yet, those around me maintain shape constancy—they still basically know what I look like. So even when things are moving, we are still able to maintain that shape constancy. We have some sense of what that lion looks like—whether it’s coming towards us, away from us, sprinting, etc. And here you can see—you know that this is a round quarter, even though at different angles it can appear quite different. coins that look different shpaes but are not Size constancy. So, when I walk far away you don’t say, “Gosh, she is getting smaller,” you say, “Oh, she is further away—she is still about 5 feet 9 inches tall.” When I walk up close to you, you don’t say, “Oh my gosh, she just turned into a giant.” You recognize those differences. And so you maintain size constancy in ever-changing circumstances. I think it is important to recognize that we develop these perceptual skills over time. A small child can get really freaked out if you change your hair. I remember the first time I put my hair up in a bun when my son was very young; my son looked very confused, like he wasn’t quite sure it was me. This is an example of the evolving shape constancy. These kinds of perceptual expectations are emerging across development and suddenly you have a child who can do these things pretty well. Do You Remember? See what you can remember from the material on sensation and perception by matching the terms with their definitions. Review and Reflect