4 Genes, Environment, and Behavior • Genetic determinism: The idea that genes alone determine everything about us, including behavior. • “Nature versus nurture” is the debate of how much of our behavior results from genes and biological influences, and how much is influenced by our environment and how we are raised. • This “debate” assumes that nature and nurture are two distinct influences. The Marshmallow Test –To understand when the control of delayed gratification develops in children. –600 children studied –A small percentage ate the marshmallow immediately. Those who attempted delayed gratification, about 1/3 made it long enough to get the second marshmallow. –Age was a major determinant of deferred gratification. https://www.youtube.com/watch?v=QX_oy9614 HQ • Proteins are the building blocks of life. They form cell structures and regulate all the processes that keep cells alive. • The cell nucleus contains the chromosomes, which are long, twisted strands of DNA. • A gene is a specific length of DNA that encodes the information needed to make one or more proteins. • Proteins are composed of subunits called amino acids. • There are 20 different amino acids. The sequence of amino acids determines the structure and function of the protein. • A gene has the information that determines the sequence of amino acids in a protein. • If the amino acids are strung together in the correct order, the resulting protein will have the right shape to do its job. • But if the amino acids are in the wrong order, or an incorrect amino acid is inserted, the protein may have the wrong shape and may not work the way it should. • Humans have 23 pairs of chromosomes. • One set comes from the father, within the sperm, and one set from the mother, within the egg. • At fertilization, the two sets come together to form the whole complement of 46 chromosomes. • The 2 chromosomes in each pair contain the same genes, but they may be slightly different, having slightly different “recipes” for how to make the protein. • Different versions of a gene are called alleles. • In most cases, you have two different alleles for each of your thousands of genes, one from your father and one from your mother. • For most genes, many different alleles exist in a population. Figure 4.4 Differing Alleles Result in Different Versions of a Protein • Mutation: A change in DNA sequence that results in changes in the instructions for making a protein. • Most mutations arise from copying mistakes when DNA is replicated during egg and sperm production. • Many are minor and have no effect on the protein’s function. • Some mutations are harmful. Substitution of one or more amino acids can disrupt protein function. • Although rare, mutations can result in better protein function or a protein that has some new, beneficial function. • If a mutation proves to be beneficial and helps the individual survive and reproduce, it may be passed on to offspring and eventually become more common in the population. • Because you have two alleles for every gene, even if one produces a nonfunctional protein, the other allele probably produces a functional one. • Most alleles make functional proteins, but the proteins may function slightly differently, which can result in slightly different traits. • Genotype: The genetic information you received from your parents. • Phenotype: The sum total of all the physical characteristics of an individual, including behavior. • Genotype does not change throughout an individual’s lifetime, but phenotype can change day to day. Figure 4.5 Genotype versus Phenotype • Some alleles influence phenotype more than others do. • Example: Flower color in pea plants. • Plants with purple flowers have at least one allele that produces a purple pigment. • Plants with white flowers have no alleles that produce purple pigment. – If a plant has one allele for purple flowers, and one allele for white flowers, all the flowers will be purple. • The purple allele is said to be dominant. – White flower color appears only if the plant has two white alleles. • The white allele is said to be recessive. Figure 4.6 Alleles at Work in Pea Flower Blossoms • Every cell carries a full set of genes, but uses only a subset of those genes. • Gene expression: When a cell uses a gene to make a particular protein. • Cells may increase or decrease expression of a gene as requirements change in response to the environment. • How do cells control gene expression? • Segments of DNA that lie adjacent to genes can determine which genes will be expressed. – These DNA segments can control when and how a gene a gene is expressed, for instance, how much of a pigment protein is made. • The fact that gene expression in the brain changes constantly in response to experience explains why both nature and nurture influence human behavior. • Experiences early in life have an especially profound and long-lasting effect on gene expression in the brain— and hence on behavior. • Epigenetics: The study of factors that affect gene expression. • Experience and the environment are epigenetic factors. • Research using two strains of mice that have different behavior patterns showed evidence of gene-environment interaction. • A classic study of gene-environment interaction used two strains of rats, one selected for rapid maze learning, the other for having poor maze-solving ability. • They showed that genes influence mazelearning abilities. Figure 4.10 Gene-Environment Interactions (Part 1) • But further research showed that the rat’s environment was also important in learning. • Rats were raised in three environments: a standard lab cage; a more impoverished environment with nothing to do; and an enriched environment with toys, wheels, and companions. Figure 4.10 Gene-Environment Interactions (Part 2) • Both strains of rats did well at maze solving if they were raised in enriched environments. • Both strains performed poorly if they were raised in impoverished environments. • The genetic differences were only apparent in the standard environment. Figure 4.10 Gene-Environment Interactions (Part 3) • For most human behaviors, no single gene is responsible. Many genes each have a small effect, along with environment and experience. • But there are some cases in which a single gene is the cause of certain behaviors. • These behaviors are either destructive processes or sensory defects. • Some alleles code for proteins that cause damage. • In many cases, a fetus with such an allele will not survive. Other alleles cause problems later in life. • Example: The gene huntingtin has one allele that becomes active in middle age, making a protein that kills certain brain neurons, resulting in Huntington’s disease. Figure 4.11 A Destructive Protein • The harmful allele for huntingtin is dominant. • Most dominant harmful alleles are rare because the person does not live to pass it on to offspring. • Each child of a person with Huntington’s disease has a 50% chance of getting the disease. • Now children of people with Huntington’s disease can choose to be tested to see if they carry the harmful allele. • Schizophrenia is a mental disorder characterized by hallucinations, delusions, disordered thinking, and emotional withdrawal. • There seems to be a clear genetic component to the disease. • But closely related people often have the same environment and similar experiences. • Thus the genetic component and environment are confounding variables—which one is at work? Figure 4.15 The Heritability of Schizophrenia • Twin studies: Twins have the same mother, develop in the same uterus, are born at nearly the same time, and usually grow up in the same environment. • Identical or monozygotic twins: A single embryo splits into two; the twins have exactly the same genes. • Non-identical or dizygotic twins: Two different sperm fertilize two different eggs at the same time; same amount of genetic relationship as normal siblings. Figure 4.16 Monozygotic versus Dizygotic Twins • In general, monozygotic twins are more alike than dizygotic twins in both physical characteristics and behaviors. • Twins are concordant for a trait if both individuals have that trait. • Twins are discordant for a trait if one has it and the other does not. • Monozygotic twins are more likely to be concordant for behaviors such as schizophrenia than dizygotic twins are. • A trait is heritable if it is influenced by one or more genes inherited from the parents. • Heritability is a statistical estimate of what percentage of variation for a trait is caused by the various genotypes. • Variation in genes accounts for 20% to 70% of the variation in every human behavior. • This means that 30% to 80% of the variation in behaviors is accounted for by environment. • If the heritability estimate for schizophrenia is 0.60, about 60% of all the variability in schizophrenia in the population is due to variability in the genes in that population. • Heritability estimates only tell us about populations of people, not about a particular person. • Adoption studies: When twins are raised apart from each other. • In twins raised apart where one develops schizophrenia, the other twin is much more likely to develop the disorder than the general population. • The concordance rate for schizophrenia is higher in monozygotic twins raised apart than in dizygotic twins raised apart. • What environmental factors are important in schizophrenia? • Studies show that exposure to stressors such as disease, malnutrition, and neglect increase the likelihood of developing the disease. • City life is more stressful than rural life; the incidence of schizophrenia is higher in cities. • The proportion of people who develop schizophrenia also increases during times of social upheaval, such as wars. • Most people develop symptoms when they are transitioning from adolescence to adulthood, a very stressful time. • The strongest evidence for the role of stress comes from twin studies. • Many studies of identical twins discordant for schizophrenia indicate that the twin who developed schizophrenia was subjected to greater stress, such as complications at birth. • Even early in life, the twin who will develop schizophrenia shows impaired motor development, suggesting that stresses very early in life may be crucial. Figure 4.18 Interaction of Stress and Genes in Schizophrenia • Our genotype is set at fertilization, and there is nothing we can do to change which genes we carry. • It is clear that genes have powerful effects on the way our body and brain are assembled. • But how genes are expressed is constantly changing in response to our environment. • Genes and experiences are equally important. • Early experiences may also epigenetically affect stress responses in adults. • In rats, some mothers are more attentive to their pups than others. These pups grow up to be less fearful and show less response to stress. Figure 4.19 Early Experience Imprints Genes to Affect the Stress Response in Adulthood • Neurons in the brain have receptors for the stress hormone corticosterone. • Corticosterone reaching these receptors triggers the brain to signal the adrenal glands to reduce production of the hormone. • In rats with inattentive mothers, the genes for these receptors are modified by methyl groups, which reduces gene expression, and thus fewer receptors are made. • The adult rats make fewer receptors, and thus release more corticosterone. • In rats with attentive mothers, a protein cofactor binds to the receptor gene, which prevents methylation. • These adults express the receptor gene more, and thus produce less corticosterone. • Studies on the brains of suicide victims also show the addition of methyl groups on the gene for the stress hormone receptor—but only in victims who had been abused or neglected as children. • The implication is that early neglect epigenetically modified expression of the gene in these people. 5 Developmental Psychology Developmental psychology: The study of how the mind and behavior progress as an individual grows. Developmental psychologists once focused only on infants and children, but now recognize that we never stop developing. Brain development involves addition of new neurons and connections, but also loss of neurons and synapses. Experience determines which cells and connections will be lost and which will be retained. Every human starts out as a single cell—the zygote, or fertilized egg. The zygote divides to form a sphere of cells— the embryo. In mammals, the outer layer of cells forms the placenta, which implants into the uterine wall and provides nutrients and oxygen to the embryo. The inner cell mass of the embryo continues dividing to form the body. By about the 9th week the embryo is called a fetus. The nervous system starts as a hollow neural tube. One end becomes the brain, the other end becomes the spinal chord. Brain development proceeds in six stages. 1. Neurogenesis Dividing cells become neurons. Cells are added rapidly; most of our neurons form before birth. 2. Cell migration Neurons move and begin to form clumps of cells that will become brain regions. 3. Differentiation Neurons develop into different types. 4. Synaptogenesis Making the billions of connections, or synapses, between neurons. 5. Neuronal cell death Many cells formed earlier die, perhaps because they have inappropriate connections. This process stops before birth. 6. Synapse rearrangement Some synapses are lost and others form. This process continues throughout life. During childhood, more synapses are gained than lost. Brain size of the fetus increases dramatically as neurons are added. After birth, the brain continues to grow due to addition of billions of synapses. Experiences during this time have an enormous impact on the brain. As the fetal brain is growing rapidly, it is vulnerable to poor nutrition and harmful chemicals. Teratogen: A substance that disrupts development and results in malformations. Teratogens include chemicals in cigarette smoke, pollutants, and alcohol. Consuming alcohol during pregnancy can result in fetal alcohol syndrome (FAS). Children with FAS have distinct facial features and mental impairment such as reduced language and fine motor skills, and aggressive behaviors. Severe impairment includes failure to develop the corpus callosum, which connects the cerebral hemispheres. Experience plays an important role in guiding brain development. Visual experiences early in life influence synapse rearrangement necessary for sight. Animal research shows that if an eye is deprived of light for too long, synaptic connections with the brain are lost forever, and the eye will be blind. But depriving the adult eye of light has no effect. Sensitive periods: times during development when events, such as light deprivation, can have a large effect on brain development and later behavior. When surgeons began to remove cataracts from adults who had been born with them, they found that sight was not restored. The synapses from eye to brain had been lost forever in these people. Plasticity: Ability of the brain to change. Developing brains are much more plastic than adult brains. Children with brain damage typically have much greater recovery of brain function than adults—a reflection of the greater plasticity in synapse rearrangement in the young brain. Newborns display many simple reflexes: unlearned, automatic responses to specific stimuli. Examples: grasping reflex, rooting reflex, and sucking reflex. Motor development: Babies show progressively complex movements. Figure 5.7 Milestones in Infant Motor Development Development is affected by both genes and the environment. Researchers determined that babies were more likely to die of sudden infant death syndrome (SIDS) if they lived with cigarette smokers or were placed on their tummy to sleep. Figure 5.8 Back to Sleep But subsequent research shows that sleeping on the back slows progression of motor milestones. Babies lying on their back have fewer chances to explore and experiment on their belly, and this appears to slow their ability to creep and crawl. Together, experience and genes determine the pace of development. Along with motor systems, sensory systems are also developing. Newborns have poor vision compared to adult vision because the neurons in the retina and the synaptic connections to the brain are immature; they lack the resolution of adult vision. Figure 5.9 Infant Vision Rapidly Improves By the time infants begin crawling, their vision is developed enough that they refuse to crawl over a visual cliff—an apparent drop off in the floor. Even 2-month old babies apparently have some depth perception. Figure 5.10 The Visual Cliff https://www.youtube.com/ watch?v=WanGt1G6ScA Auditory systems seem to be more mature at birth than visual systems, possibly because the child has been receiving auditory stimulation in the uterus. Infants prefer sounds that resemble speech, which probably helps them acquire language. How do we know what infants perceive? Researchers must infer this from infants’ behavior. Example: Tracking eye movements If an infant spends more time looking at one image when presented with two images, we infer that the infant prefers one over the other, or finds it more interesting. Even very young infants prefer looking at facelike images to almost anything else. The more an object looks like a face, the more time infants spend looking at it. This preference grows stronger as they grow older. If an infant looks at one picture more than another, we conclude: • She can tell the two pictures apart. • She prefers one over the other. If the infant looks at two images for the same amount of time, they might not be distinguishable, or there is no preference. Habituation: Failure to attend to a familiar stimulus. Babies may look at a new image for a while, but then their gaze moves to other objects. Habituation technique: By varying the amount of difference between images, researchers can track the development of the visual system in infants. https://www.youtube.com/watch?v=uAl3y3zIp uk Cognitive development: Progressive increase in cognitive ability, including reasoning, problem solving, and language. Swiss psychologist Jean Piaget (1896–1980) was the first to think of a child’s brain as being organized differently than an adult’s brain. As the child grows, she reorganizes thought processes in successive stages of complexity, until she begins to reason like an adult. Piaget’s ideas: The child is an active participant in the development of her own mind (constructivism). • Adaptation to the world: ▪ Assimilation: Taking in information about the world. ▪ Accommodation: Change made in the mind as a result of taking in that new information. Figure 5.16 Piaget’s Constructivist View of Mental Development in Children Piaget’s ideas: There are four distinct stages of cognitive development that a child must go through to think like an adult. Each stage builds on the previous one, and children must completely accommodate one stage of thinking before they can properly assimilate information in the next stage. The principles learned at each stage reflect a cognitive structure inside the mind, which Piaget called a schema. Sensorimotor stage: First 2 years of life • Learning how to use the sensory system and control the body • Learning to distinguish ourselves from other things and other people • Learning object permanence—objects continue to exist even if we cannot see or hear them Figure 5.17 Object Permanence Preoperational stage: Ages 2 to 7 • Language learning • Egocentrism, the notion that everything revolves around them and that everyone knows what they know • They do not yet have a theory of mind: the understanding that other people’s minds are different from their own and may have different information Figure 5.18 The Sally and Anne Test Children at the preoperational stage still reason intuitively rather than logically. They must acquire an understanding of conservation: the volume and mass of an object remain the same no matter how you rearrange its parts. Figure 5.19 Testing a Child’s Understanding of Conservation https://www.youtube.com/wat ch?v=gnArvcWaH6I Concrete operational stage: Ages 7 to 11 • Learn more formal logical skills, but tend to be very concrete in their thinking • Readily learn mathematical operations such as addition and multiplication • Have trouble with more theoretical questions Formal operational stage: About age 11 • Able to consider many different theoretical possibilities for a condition • Solve complex, hypothetical problems using abstract ideas • Can engage in hypothesis testing • Become concerned with the future and with ideological questions Figure 5.20 Piaget’s Four Stages of Cognitive Development Temperament: A person’s emotional makeup; the way he or she generally responds to situations. Considered a long-lasting aspect of personality and usually thought of as inborn. In developmental psychology, it refers to differences in emotional response that are seen in infants and seem to persist throughout life. Temperament has a genetic component, but environment also plays a role. For example, difficult infants became less difficult if their parents were able to respond in a patient, relaxed fashion to their demands. Stranger anxiety: A milestone in infant emotional development when they have a negative response to unfamiliar people. Child psychologist John Bowlby proposed that human infants are also born with the tendency to form a strong emotional attachment to his or her caregivers. The child uses them as a “safe base” from which to explore the world. The child uses this early social interaction with his caregivers to build social relationships with other people. Psychologist Mary Ainsworth devised the strange situation, a test of the attachment between child and parent as revealed by the child’s reaction to separation from the parent. Secure attachment: The child is visibly upset when the caregiver leaves, rejects a stranger, and is happy when the caregiver returns. https://www.youtube.com/watch?v=QTsewNrHUHU Avoidant attachment: The child shows little or no distress when the caregiver leaves, little or no response upon reunion, and interacts very little with a stranger. https://www.youtube.com/watch?v=AGRT6VjnTm8 Figure 5.23 Different Types of Attachment Styles Ambivalent or resistant attachment: Child is upset when the caregiver leaves, but may warm up to a stranger, and behave negatively toward the caregiver upon reuniting. Disorganized attachment: Child shows an inconsistent pattern of response in the strange situation. https://www.youtube.com/watch?v=DRejV6fY3c Responses to the strange situation often correlate with behavior later in life. Responses also correlate with parenting style. It is not clear whether the adult’s parenting style causes the attachment pattern, or whether the infant’s attachment pattern shapes the parent’s behavior. Puberty: When an individual becomes capable of reproducing—production of sperm or release of eggs. Puberty is an event; adolescence is the process of transition from childhood to adulthood. Adolescence is marked by physical changes. There is a brief, vigorous growth spurt, with changes in body proportions. Hormones (estrogen and testosterone) drive the development of secondary sex characteristics. These changes affect how other people relate to the individual, and tell the individual that he or she must prepare for the transition to adulthood. Many studies show that children in Western nations reach puberty at earlier ages than they used to. An indicator of puberty in girls is menarche: the girl’s first menstrual period. Possible explanations of this accelerating menarche include better nutrition and medical treatment, exposure to human-made chemicals in the environment, or increased body fat. Social experience may be a factor: • If a father is present during the first 10 years of life, girls enter menarche later than girls with an absent father. • The more stress a girl experiences, the more likely she is to reach menarche at a younger age. The brain is also changing during adolescence. Brain development is mostly complete by puberty, except for myelination (complete by about age 20) and synapse rearrangement. Greatest changes are in the frontal cortex, including areas that inhibit behavior. During adolescence, teenagers develop more control and independence, which helps them learn to make good choices. They also have the opportunity to make poor choices and engage in risky behaviors. Some studies indicate that they may make risky choices because they underestimate the unpleasant consequences. Most adolescents maintain good relationships with their parents, but also desire to make friends and spend time with them. It is a continuation of “attachment”—the parents serve as a safe base to which the child returns after forays out into the world. Peer interactions are also valuable for social development. Adolescents may experience intense mood swings, and this may explain why some become depressed. While many people recover from adolescent depression, there is also a peak in suicide at these ages. Many of these suicides seem to be impulsive acts, so intervention can be important. https://www.youtube.com/watch?v=3BByqa7bhto Antidepressant drugs are modestly effective in adults, but seem to have little effect in children and teens. Some studies indicate teens are more likely to commit suicide while taking antidepressants. • One pitfall seems to be when teens decide on their own to stop taking the antidepressant. The biggest challenge of adolescence is developing a personal morality. Morality is a set of rules determining whether conduct is right or wrong. Many people are telling adolescents what is right and wrong, and they do not all agree. There is often conflict between what a person emotionally feels is right and what seems proper if we use reasoning. Lawrence Kohlberg (1927–1987) believed there are distinct stages of moral reasoning that we go through, and we must achieve competence in each stage before we can grasp the next. Most adults use conventional moral reasoning, based on society’s expectations. Young children use preconventional moral reasoning, based on personal consequences. Few people achieve postconventional moral reasoning (the “principled level”), in which rules are based on a social contract. At the highest level of moral reasoning, a person may reject rules even when the majority of citizens disagree. Kohlberg’s ideas on moral development have been criticized: • Studies have shown that children may use preconventional or conventional moral reasoning depending on whether an action would cause someone to be hurt. • Emphasis on justice, rather than caring. From a caring orientation, the three stages of moral development can be seen as: 1. What is good or bad for only me? 2. What is good or bad for other people? 3. What is good or bad for everyone, including me? Sometimes orientations of justice (what is fair?) can be in conflict with orientations of care (is someone suffering?). https://www.youtube.com/watch?v=dzmNoFnx u68 Erik Erikson (1902–1994) suggested there are eight stages of psychosocial development, marked by shifts in our relationships with other people. The stages are progressive—experiencing one stage tends to lead to the next. Each stage is characterized by tension; we are torn between opposing ways of interacting with people. Criticism of Erikson’s theory: • It was not based on empirical data, but inspired by biographies of famous people. • It was inspired by Freud’s theories, which were also based on anecdotes. But it has withstood the test of time; the stages resonate with most people’s personal experiences. Aging Physical changes: skin becomes less supple, hair thins and grays, reproductive systems begin to shut down, hormone levels decline. Menopause: When menstrual cycles stop, around age 50. For men, the reproductive shutdown is more gradual, also starting around 50. Vision and hearing may gradually become less acute. Decreased functioning of sensory and motor systems contributes to some decline in information processing. Reaction times become slower, such as hitting the brake pedal when a light comes on. • Drivers 75 and older are much more likely to have an automobile accident. Many brain regions have a net loss of neurons. The average length of dendrites becomes shorter, indicating a loss of synapses. Overall brain weight shrinks by 10% by age 90. Some regions show more shrinkage than others, for unknown reasons. Keeping physically and mentally active can slow down brain shrinkage as we age. There is a progressive decline in memory skills; but also a great deal of variability among individuals. In normally aging people, there is a correlation between the strength of memory and the size of the hippocampus, which is important for memory. Is there a decline in intelligence with aging? Two different kinds of intelligence: Fluid intelligence—ability to think and reason abstractly and to solve problems. Crystallized intelligence—learning from past experience, based on a store of facts. Young adults have greater fluid intelligence, but the elderly tend to have greater crystallized intelligence. Fluid intelligence peaks in adolescence but begins to decline at around 30–40. Crystallized intelligence keeps growing throughout adulthood, except in extreme old age or pathology, such as Alzheimer’s disease. Figure 5.33 Changes in Intelligence with Age Perceptual speed—how quickly we can detect and process stimuli—steadily declines with age. In timed visual tests, young adults performed better than elderly adults. But if elderly adults were given more time, they performed just as well. Figure 5.34 Perceptual Speed in Vision Declines with Age Some people show signs of dementia— progressive decline in cognitive function caused by damage or disease rather than normal aging. It is marked by growing forgetfulness; impairment in language, perception, and judgment; or a change in personality. The two major causes are a series of small strokes and Alzheimer’s disease. Alzheimer’s disease results from a buildup of abnormal clumps of dead and dying neurons called neuritic plaques in the brain. Brain cells release a protein called amyloid, which accumulates in pockets and causes the plaques to form. Genetic component: people with certain alleles for some proteins are more likely to develop Alzheimer’s. Alzheimer’s disease is not simply a result of the brain wearing out. AD may occur before age 60; but people who live to age 90 are less like to develop AD. Many studies have shown that remaining physically and intellectually active makes a person less likely to develop AD. Participating in social activities also helps preserve cognitive function. 8 Learning 8 Introduction In 1919, John Watson did experiments with an infant (Little Albert) to study learning. He paired loud harsh sounds with the presentation of a white rat, and Albert soon learned to be afraid of the rat, and subsequently all furry objects. Watson never knew whether this fear would persist because Albert and his mother moved away. The study would be considered unethical today, and Watson was publicly criticized. 8 Introduction Learning: The acquisition of knowledge, skill, attitudes, or understanding as a result of experience. Generally we are interested in learning that results in a relatively long-lasting change in behavior. Little Albert displayed conditioned learning, he was conditioned to associate a white rat with a loud, upsetting noise. Figure 8.1 The Conditioning of Little Albert https://www.youtube.com/wat ch?v=zZ3l1jgmYrY 8.1 Predicting the Future Stimulus: Any physical event that affects a sensory cell so that an individual can detect the event. The simplest learning involves a single stimulus. Habituation: Repeated presentation of a stimulus elicits less and less of a response. • If the subject is still able to detect the stimulus and respond, then the reduced responsiveness must have been learned. Figure 8.2 Habituation in Humans and Slugs 8.1 Predicting the Future Even simple animals habituate. Sea slugs become habituated to gentle squirts of water that initially cause the animal to withdraw its gill. In habituation, the sensory system does not lose the ability to detect the stimulus. The animal learns to ignore it. 8.1 Predicting the Future In sensory adaptation, the sensory system stops responding to an unchanging stimulus, which reflects the way sensory receptor cells are built. In habituation, the animal can still detect the stimulus. They serve the same purpose: helping us ignore repetitive or constant stimuli that are not important for survival. 8.1 Predicting the Future Dishabituation: The sudden return of a response that had formerly been habituated. An electric shock applied to the sea slug’s tail causes the animal to again withdraw its gill when squirted with water. The sea slug also becomes sensitized: a very strong unpleasant stimulus causes an enhanced response to a variety of other stimuli. Figure 8.3 Dishabituation and Sensitization in Humans and Slugs 8.1 Predicting the Future These simple forms of learning (habituation, dishabituation, and sensitization) are called non-associative learning: • There is no particular predictive relationship between any two stimuli. 8.1 Predicting the Future Associative learning: Learning of the relationship between two stimuli or a stimulus and a behavior that repeatedly occur at about the same time. • Classical conditioning • Operant conditioning 8.1 Predicting the Future Classical Conditioning In the famous experiments of Russian physiologist Ivan Pavlov, a bell was rung every time meat powder was placed in a dog’s mouth, triggering salivation. The dog learned to associate these paired stimuli, and would then salivate when the bell sounded. Figure 8.4 Russian Physiologist Ivan Pavlov (1849–1936) Figure 8.5 Classical, or Pavlovian, Conditioning 8.1 Predicting the Future Terminology in classical conditioning studies: Unconditioned stimulus (US)—naturally evokes a specific response (reflexive). Unconditioned response (UR)—specific response naturally evoked by the US. Conditioned stimulus (CS)—neutral stimulus paired with the US, eventually triggers the response. Conditioned response (CR)—learned response to a previously neutral stimulus. 8.1 Predicting the Future Acquisition—gradual appearance of the CR in response to the CS. Humans can also learn by classical conditioning. Classical conditioning allows animals to “predict the future” and is adaptive. 8.1 Predicting the Future Stimulus generalization: When the subject displays a CR to stimuli that are similar, but not identical, to the CS used in training. • Example: Dogs conditioned to salivate at a tone of middle C will also salivate at tones near middle C. Little Albert was showing stimulus generalization when he was afraid of any fuzzy thing. 8.1 Predicting the Future If a dog is repeatedly presented tones of different pitch, but only given food when the pitch is middle C, it will learn to salivate only at that pitch. The dog is displaying stimulus discrimination. 8.1 Predicting the Future Extinction: Repeated presentation of the CS (sound) without the US (food) results in weaker and weaker CR, until the CR disappears. The CR will reappear faster if the pairing of CS and US is resumed. Spontaneous recovery: The previously extinguished CR in response to the CS returns after a period of rest. Figure 8.8 Acquisition, Extinction, and Spontaneous Recovery in Classical Conditioning 8.1 Predicting the Future For a while it seemed that all stimuli were equal in eliciting the CR, but the work of John Garcia showed that some associations are more easily learned than others. • Question: Are all stimuli really equal in their ability to invoke an unconditioned response? • Hypothesis: It may be adaptive to readily associate illness with taste (e.g., poisonous berries). 8.1 Predicting the Future • Test: Establish what dose of radiation would induce nausea in rats. ▪ Two groups of rats are given an US of sweetened water followed by either 1. a buzzer, a flash of light, and a shock, or 2. a buzzer, a flash of light, and enough radiation to induce nausea ▪ After conditioning both groups, give rats a choice of sweet water alone, or plain water with the light and buzzer. 8.1 Predicting the Future • Results: Rats that had been shocked associated the shock with the noise and light, not with the sweet water, and continued to drink sweet water. ▪ Rats that had been sickened associated nausea with the sweet water, and subsequently drank less sweet water than rats in the no-radiation group. 8.1 Predicting the Future Conclusion: The particular stimulus used in classical conditioning does matter. Natural selection has favored the tendency to readily associate nausea with something we previously ate or drank, which may help us avoid ingesting poisons. Figure 8.9 Taste Aversion (Part 2) Figure 8.9 Taste Aversion (Part 3) 8.1 Predicting the Future Conditioned taste aversion: Experiments showed that rats associated a new taste with nausea so readily that a single pairing was enough to cause them to avoid that taste. This disproved three ideas on classical conditioning: • All stimuli work equally well. • Repeated pairings are needed for acquisition. • The US must be presented soon after the CS. Figure 8.10 The Study of Taste Aversion 8.1 Predicting the Future Natural selection would favor taste aversion to prevent animals from eating foods that might kill them. If animals become ill, even once, after eating a new food, they avoid that food in the future. Poisonous food sometimes takes hours to evoke symptoms, so it makes sense that taste aversion conditioning can occur even if the nausea happens much later. 8.1 Predicting the Future Taste aversion conditioning also operates in the natural world. • Example: A blue jay that eats a monarch butterfly soon becomes ill and will thereafter avoid eating other such butterflies. Figure 8.11 Taste Aversion at Work 8.1 Predicting the Future People also experience taste aversion when they get sick after eating a specific food. It can be a very strong, reflexive reaction. This is evidence of its adaptive significance, as is the evidence that this learning takes place in the evolutionarily older brainstem rather than in the cortex. 8.1 Predicting the Future Taste aversion is adaptive learning. Another type of adaptive learning is imprinting: the tendency of newly hatched birds to bond with the first moving object they see and follow it. • The chick normally sees its mother first, so it learns to follow her. Biological constraints on learning (or biological preparedness to learn): some behaviors are more easily learned by one species than another. Figure 8.12 Follow Your Mother? 8.1 Predicting the Future Fear conditioning: Pairing a previously neutral stimulus with a painful stimulus. Just about any stimulus can be associated with pain. Little Albert was subjected to fear conditioning. In lab experiments, the fearful reactions can be unlearned by presenting the CS without the US (extinction). Figure 8.13 Fear Conditioning 8.1 Predicting the Future Experiences such as Albert’s can lead to a phobia, an irrational fear of particular objects or situations. Fear of truly dangerous objects, like a loaded gun or a wild animal, is by definition not a phobia. 8.2 Reinforcing Behavior In real-life conditions, we and other animals are constantly learning which of our actions bring the outcomes we want. Edward Thorndike studied learning in cats using a puzzle box—cage equipped with levers and latches; an animal must open a door to escape. The cats generally got out of the box faster with each subsequent trial, but the process seemed very gradual and rather hit-or-miss. Figure 8.14 Puzzle Boxes 8.2 Reinforcing Behavior Thorndike concluded that animals were solving the boxes by trial and error. They were learning to connect a particular response with the pleasant outcome of the door opening. The law of effect: Any behavior that results in a satisfactory outcome is more likely to recur in the future. 8.2 Reinforcing Behavior John Watson advocated behaviorism: the perspective that psychologists should only study externally visible behavior rather than make inferences about internal processes. Behaviorism dominated psychology for over 50 years, primarily due to B. F. Skinner. Skinner sought to standardize testing so he could systematically vary conditions to see how they affected learning. 8.2 Reinforcing Behavior Skinner built boxes that would hold a rat or pigeon and some simple learning task, such as pressing a bar to receive a food reward. • In this case, the animal’s behavior (bar press) elicited the stimulus (food). Skinner called this operant conditioning, and the boxes operant conditioning chambers (Skinner boxes). Figure 8.16 Learning to Press a Lever 8.2 Reinforcing Behavior Delivery of food makes the animal more likely to press the bar in the future, reinforcing that behavior. A reinforcer is a stimulus that appears in response to behavior and increases the probability of that behavior recurring. Reinforcers include food, access to a sexual partner, or receiving an injection of a drug like cocaine. Box 8.2 Skeptic at Large: Operant Conditioning for Fun and Profit Chickens can be trained by operant conditioning to “play” tic-tac-toe for food. But it is doubtful that the hen can actually choose which square to occupy next to beat her opponent. Humans who opt to try to beat the chicken at tic-tac-toe are also displaying operant conditioning: they play in hopes of getting money. Box 8.2 Who’s the Better Player? 8.2 Reinforcing Behavior Standardized Skinner boxes taught us a lot about learning. Researchers could help rats catch on more quickly by shaping: providing reinforcers whenever the subject came close to making the desired response. 8.2 Reinforcing Behavior Human behavior can also be shaped. In a classic experiment, people were told they would get a point for a particular behavior but weren’t told what the behavior was. At first participants got points for lifting a thumb, then for moving the hand, until finally only by raising a hand could they gain points. Figure 8.17 Shaping Human Behavior 8.2 Reinforcing Behavior When food was provided to pigeons at random, some birds acted as though a behavior would result in a food reward. Skinner said the birds were displaying superstition, the false belief that a particular behavior will bring about a stimulus or event. Humans also display superstitions, like baseball players. Figure 8.19 A Superstitious Athlete 8.2 Reinforcing Behavior Four types of stimuli can change behavior. Reinforcements make a behavior more likely to occur. • Positive reinforcement: When a behavior is followed by a favorable stimulus, like food. • Negative reinforcement: When a behavior is followed by removal of an aversive stimulus (escape). 8.2 Reinforcing Behavior Punishments make the behavior less likely to recur. • Positive punishment: Usually an aversive stimulus, such as spanking. It is added after the behavior. • Negative punishment: A penalty; something is removed after the behavior, such as grounding a teenager. Figure 8.20 Overview of Different Types of Reinforcements and Punishments 8.2 Reinforcing Behavior In the 1960s and 1970s debate arose regarding the use of punishment in child rearing. Punishment may make the child afraid of the parent. Some punishment is aggressive, such as spanking. Does it teach bad behavior? If punishment is used inconsistently, the child may not be able to figure out what is appropriate. Punishment may simply teach the child which behaviors to avoid when the parent is present. 8.2 Reinforcing Behavior Most experts agree that reinforcement with rewards is usually better than punishment. Punishment should be used sparingly in combination with positive reinforcements, including praise. It must come soon after the offense, and it is important to explain to the child what triggered the punishment and why it was inappropriate. Punishments must be used consistently to be effective. 8.2 Reinforcing Behavior Escape conditioning: Negative reinforcement in which the subject learns a response that removes an aversive stimulus. Active avoidance: The subject must display a particular behavior to avoid an unpleasant stimulus. Pavlov’s dogs learned to jump over a barrier to avoid an electrical shock, then were conditioned by hearing a tone before the shock. 8.2 Reinforcing Behavior Once the dogs had learned this, it was very difficult for them to unlearn it. Because they always jumped over the barrier at the tone, they could never learn that the shocks no longer occurred. The only way was to close off the barrier, so the dog could not jump over. Figure 8.21 Active Avoidance Behaviors Are Difficult to Extinguish 8.2 Reinforcing Behavior Irrational fears (phobias) have been connected to the difficulty of extinguishing active avoidance. Little Albert leaned to move away from the rat and other furry objects. If as he grew up, Albert always avoided furry things, he couldn’t learn they might be harmless. 8.2 Reinforcing Behavior Passive avoidance: Animal learns to not show a particular behavior to avoid unpleasant stimuli. In the simplest case, the animal learns to do nothing, just stay still, when the stimulus arrives to avoid shock. Some people with extreme social phobias learn to stay in their homes to avoid unpleasant situations. They never learn that some social encounters can be pleasant and rewarding. 8.2 Reinforcing Behavior Learned helplessness: The subject learns that an aversive stimulus cannot be avoided. In experiments with two dogs harnessed together, both were given electric shocks, but one dog could stop the shocks by pressing a button. The other had no control. When the dogs were later put in an active avoidance chamber, the dog that had no control over the shocks could not learn to jump the barrier; it had learned helplessness. 8.2 Reinforcing Behavior Learned helplessness may be a model for clinical depression, which is typified by disinterest in being active and lack of belief that taking action will improve things. Not all dogs seemed to be susceptible to learned helplessness; some would readily learn to jump the barrier. Some people seem more susceptible than others to clinical depression. 8.2 Reinforcing Behavior Reinforcement schedules: Skinner’s studies of operant conditioning led to rules governing how often a subject is given reinforcement. Continuous: Reward behavior every time it is displayed. Partial (intermitant): Only some of the responses are reinforced. 8.2 Reinforcing Behavior Fixed ratio (FR) schedule: Reinforcement is delivered after every Nth response (e.g., food after every 10 bar presses). • Subjects tend to pause in the bar pressing after the reward. Variable ratio (VR) schedule: Subject cannot predict how many responses will result in the reinforcement. • Acquisition is faster, with fewer reinforcements required. 8.2 Reinforcing Behavior The time between reinforcements can be varied, instead of number of responses required. Fixed interval (FI) schedule: Reinforcement comes after a set time period. Variable interval (VI) schedule: Reinforcement that comes after different periods of time. • Animals show more consistent performance. Table 8.1 (Part 1) Table 8.1 (Part 2) 8.2 Reinforcing Behavior Responses trained using variable schedules are generally slower to extinguish than behaviors trained using fixed schedules. These reinforcement schedules can be applied in child-rearing, in classrooms, and in the workplace. Figure 8.22 Overview of Different Types of Reinforcement Schedules 8.2 Reinforcing Behavior Primary reinforcer: Stimulus that fills a biological need (food, water, or sex), or a punishment the subject already finds unpleasant. Secondary reinforcer: Stimulus the subject comes to associate with one or more primary reinforcers. • The money that we work for in a job is a secondary reinforcer—it provides access to food, water, shelter, etc. 8.3 Observational Learning Behaviorism ignored other types of learning because studying them requires speculating about internal, mental processes. But by the mid-20th century, investigators began to consider how animals were learning in addition to conditioning. 8.3 Observational Learning Rats learning to run a maze for a food reward can be viewed as operant conditioning. Tolman suggested that when rats first wander the maze, they are building a cognitive map of the maze. • Rats quickly know to use alternate routes if the main route is blocked. Figure 8.23 Rats Can Form a Cognitive Map 8.3 Observational Learning Modern studies have shown that certain neurons in the hippocampus fire when the rat is in a particular part of the maze. In humans too, neurons in the hippocampus fire when the person is in a particular location. This part of the brain seems to keep track of where we are in space. Natural selection would favor development of cognitive maps for finding food, mates, etc. 8.3 Observational Learning Tolman also did experiments to show learning could take place even with no reinforcement. • Question: Can rats learn only in response to a reinforcement such as food? • Hypothesis: Rats exploring a maze will learn about that maze even if there is no reinforcer such as food. 8.3 Observational Learning • Test: Allow rats to explore a maze with one-way doors so they eventually reach the goal box. ▪ Divide rats into three groups: 1. Food is provided in the goal box every day 2. Food is provided only on the 11th day 3. Food is never provided Figure 8.24 Latent Learning in a Maze (Part 2) 8.3 Observational Learning • Results: Rats receiving food from the beginning quickly learned to go there with few errors. ▪ Rats provided no food until the 11th day made many errors up to that point. But on the 12th day, after having found food in the goal box the day before, these rats made even fewer errors than the rats provided food all along. ▪ Rats that were never given food continued to make errors. 8.3 Observational Learning • Conclusion: The rats provided no food for the first 11 days must have learned about the maze—on the 12th day they made no more errors than rats given food all along. ▪ Animals can, in fact, learn about a maze even in the absence of reinforcement. This is an example of latent learning— occurs without being immediately apparent and often without reinforcement. Figure 8.24 Latent Learning in a Maze (Part 3) 8.3 Observational Learning Observational learning: One individual learns by watching another individual’s behavior. Modeling: one individual imitates another’s behavior. Modeling has been documented in many animals, including Japanese macaques and blue tits. One individual tried a behavior that resulted in a reward of sorts, and other individuals imitated that behavior. Figure 8.25 Observational Learning 8.3 Observational Learning Many birds learn their characteristic songs by hearing their father’s singing. • This can result in regional “dialects” — song variation from place to place. Babies also learn to speak the language and dialect that they hear while growing up. Figure 8.26 White-Crowned Sparrow Dialects 8.3 Observational Learning Youngsters of many animal species engage in rough-and-tumble play: running, chasing, wrestling, etc., especially males. Play behavior may influence adult behavior. Monkeys raised without the opportunity to play grow up to be socially inept, unable to mate or get along with other monkeys, or care for their young. 8.3 Observational Learning Human children spend more time in play than other species. Even children playing alone often pretend to be interacting with other people (e.g., playing with a doll). Play teaches us how to interact with other people. It is one aspect of social learning— changes in behavior brought about by interacting with other individuals. 8.3 Observational Learning Bandura studied social learning using a Bobo doll. He did experiments in which children observed adults interacting with Bobo. Children exposed to adults who displayed aggressive behavior towards Bobo were more likely to also show aggressive behavior. On average, boys were more aggressive than girls, especially if the model was a man. Figure 8.27 Bandura’s Four Factors Necessary for Modeling Behavior https://www.youtu be.com/watch?v=z erCK0lRjp8 8.3 Observational Learning People emulate modeled behavior when four criteria are met: 1. Paying attention to the model’s behavior 2. Retaining the information gained about the observed behavior 3. Reproducing the behavior, and getting better at imitating the behavior with practice 4. Motivation to reproduce the model’s behavior 8.3 Observational Learning Bandura’s results suggest that behaviors can be learned without the external reinforcers emphasized in behaviorism. But reinforcement was important in motivation: children, especially girls, were unlikely to imitate the behavior if the model was punished for it. Social monitoring or referencing: When an individual observes consequences of someone else’s behavior to guide their own behavior. 8.3 Observational Learning Insight: A sudden understanding of a problem that leads to a solution without having to resort to trial and error. Köhler studied insight in chimpanzees in the 1920s. Films show them solving problems (how to get at suspended bananas), but not by trial and error. Figure 8.28 Insightful Problem Solving in Chimpanzees 8.3 Observational Learning Insight in humans: the candle problem requires thinking of a new use for an object. This type of insight is often crucial for insightful learning and is a pretty good definition of what we mean when we say someone is creative. Figure 8.29 The Candle Problem https://www.youtube.com/watch ?v=FRtQNS5dFO8 8.3 Observational Learning It is unclear whether Little Albert developed a life-long phobia of furry objects. He may have been one of two boys born to unwed mothers at Johns Hopkins hospital where Watson worked. One boy died at age 6 of hydrocephalus. The other boy lived to age 87, and relatives report that he always hated dogs and never had any pets.
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