* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 6 – Perception
Behavioral modernity wikipedia , lookup
Educational psychology wikipedia , lookup
Thin-slicing wikipedia , lookup
Theory of planned behavior wikipedia , lookup
Attribution (psychology) wikipedia , lookup
Abnormal psychology wikipedia , lookup
Theory of reasoned action wikipedia , lookup
Psychophysics wikipedia , lookup
Applied behavior analysis wikipedia , lookup
Neuroeconomics wikipedia , lookup
Adherence management coaching wikipedia , lookup
Learning theory (education) wikipedia , lookup
Verbal Behavior wikipedia , lookup
Behavior analysis of child development wikipedia , lookup
Insufficient justification wikipedia , lookup
Social cognitive theory wikipedia , lookup
Classical conditioning wikipedia , lookup
Behaviorism wikipedia , lookup
Chapter 8 – Learning – ‘15 Learning: experience; know sequence, association for both classical and operant conditioning CC: OC: Classical Conditioning: Pavlov, Watson, behaviorism, principles UCS UCR CR NS/CS Terms (for both): acquisition: timing, extinction, spontaneous recovery, generalization, discrimination, Updating: “mentalistic” cognitive processes (predictability), biological predispositions – Garcia experiment showed 1. 2. Pavlov’s legacy: scope, methodology, application, influence on Watson, “Little Albert” Versus Operant conditioning: BF Skinner: Law of Effect, Skinner Box, shaping / successive approximations Reinforcers: positive and negative, primary, conditioned / secondary -immediate versus delayed (marshmallow test) -continuous versus partial -partial / intermittent reinforcers and effects: fixed ratio (FR), variable ratio (VR), fixed interval (FI) – “scalloped, variable interval (VI) Punishment definition, problems with: Updating Skinner: Cognition, cognitive map, latent learning, overjustification effect – intrinsic versus extrinsic motivation, informational rewards versus bribes, controlling; biological predispositions Skinner’s legacy: controversy; application of operant conditioning: at school – “teaching machines”, branching at work: for managers; at home – parents, you: Observational: AKA modeling -- us, monkeys; memes, mirror neurons; -by 14 months, copy TV *Bandura: “Bobo” experiment; lowered inhibitions, copied model; -bad: hypocrites - antisocial; good: Gandhi - prosocial, -TV: not an accurate world, spread coincided with rise in violence -- definitely correlated; -consensus: does lead to violence in kids and teens; desensitizes. Chapter 8 – Learning – ‘15 Learning: experience; know sequence, association for both classical and operant conditioning CC: OC: Classical Conditioning: Pavlov, Watson, behaviorism, principles UCS UCR CR NS/CS Terms (for both): acquisition: timing, extinction, spontaneous recovery, generalization, discrimination, Updating: “mentalistic” cognitive processes (predictability), biological predispositions – Garcia experiment showed 1. 2. Pavlov’s legacy: scope, methodology, application, influence on Watson, “Little Albert” Versus Operant conditioning: BF Skinner: Law of Effect, Skinner Box, shaping / successive approximations Reinforcers: positive and negative, primary, conditioned / secondary -immediate versus delayed (marshmallow test) -continuous versus partial -partial / intermittent reinforcers and effects: fixed ratio (FR), variable ration (VR), fixed interval (FI) – “scalloped, variable interval (VI) Punishment definition, problems with: Updating Skinner: Cognition, cognitive map, latent learning, overjustification effect – intrinsic versus extrinsic motivation, informational rewards versus bribes, controlling; biological predispositions Skinner’s legacy: controversy; application of operant conditioning: at school – “teaching machines”, branching at work: for managers; at home – parents, you: Observational: AKA modeling -- us, monkeys; memes, mirror neurons; -by 14 months, copy TV *Bandura: “Bobo” experiment; lowered inhibitions, copied model; -bad: hypocrites - antisocial; good: Gandhi - prosocial, -TV: not an accurate world, spread coincided with rise in violence -- definitely correlated; -consensus: does lead to violence in kids and teens; desensitizes. Chapter 8 Notes (Complete) Learning I. Learning A. Adaptability: our capacity to learn new behaviors that enable us to cope with changing circumstances i. Unlike salmons, which have most of the behavioral instructions they need for life through genes, humans mostly learn from experience B. Learning: a relatively permanent change in an organism’s behavior due to experience i. What is learnable can potentially be taught ii. What has been learned can potentially be changed by new learning iii. Experience is key to learning C. We learn by association i. Associative learning: learning by linking certain two events that occur close together. The events may be 2 stimuli (classical conditioning) or a response and its consequences (operant conditioning) ii. Our minds naturally connect events that occur in sequence, therefore, we associate them iii. If, after seeing and smelling fresh bread, you eat some and enjoy it, the next time you see and smell fresh bread your experience will lead you to expect that it will be satisfying iv. Associations: a. If you associate a sound with a frightening consequence, then your fear may be aroused by the sound itself b. If sea snail repeatedly receives an electric shock just after being squirted, its withdrawal response to being squirted becomes stronger : associates squirt with shock c. Seals repeat behaviors that prompt people to toss them food : associate the act with the reward d. The animals learn something important to their survival, to predict the immediate future D. Successful adaptation requires both nature and nurture i. Keiko, killer whale in Free Willy, had the genes to survive in the wild but not the experience ii. The Mexican gray wolves, after being bred and raised in captivity, when released into Arizona’s Apache National Forest, were unable to survive. The lone survivor was recaptured. They did not know how to run from a human with a gun. iii. Of 145 reintroductions of 115 species in the 20th century, only 11% produced self-sustaining populations in the wild iv. Learned associations influence people E. Conditioning: process of learning associations i. Classical conditioning: learn to associate two stimuli and thus to anticipate events a. Flash of lightning signals an impending crack of thunder, so we start to brace ourselves when lightning flashes nearby ii. Operant conditioning: learn to associate a response and its consequence = repeat acts followed by reward and avoid acts followed by punishment iii. Operant and classical conditioning often occur in the same situation a. A rancher herds cattle by outfitting them with pagers; after training, the animals learn to associate two stimuli—the beep on their pager and the arrival of food (classical) and their hustling to the food trough with the pleasure of eating (operant) iv. Observational learning: learn from others’ experiences and examples v. Humans adapt to environments through operant and classical conditioning, and observation a. Classical: learn to expect and prepare for significant events such as food or pain b. Operant: learn to repeat acts that bring good results and avoid acts that bring bad results c. Observational: watching others and learning new behaviors II. Classical Conditioning A. Classical/Pavlovian/Respondent conditioning: associating stimuli; a neutral stimulus that signals an unconditioned stimulus begins to produce a response that anticipates and prepares for the unconditioned stimulus. i. Pavlov’s work laid the foundation for Watson’s idea that human behavior is mainly a bundle of conditioned responses ii. Behaviorism: psychology as an observable science based on observable behaviors iii. Both Watson and Pavlov shared a disdain for mentalistic concepts, preferring observable behaviors B. Pavlov’s experiments i. He noticed that when he worked with the same dog repeatedly, the dog began salivating to stimuli associated with the food ii. Paired various neutral stimuli such as a tone, with food in the mouth to see if the dog would begin salivating to the neutral stimuli alone iii. Isolated dog to eliminate influence of extraneous stimuli; dog secured to harness; saliva diverted to measuring instrument iv. Just before placing food in the dog’s mouth Pavlov sounded a tone after several pairings of the tone and food, the dog began to salivate to the tone in anticipation of the meat v. Unconditioned response: UCR: the unlearned response: salivation vi. Unconditioned stimulus: UCS: unlearned stimulus: food vii. Conditioned response: CR: learned response: salivation in response to sound of tone viii. Conditioned stimulus: CS: learned stimulus: tone ix. Conditioned = learned; unconditioned = unlearned C. Five major conditioning processes i. Acquisition: initial learning of the stimulus-response relationship a. Question of timing: How much time should elapse between the neutral stimulus (NS) and the UCS?: generally half a second b. Conditioning would not likely happen if the food (US) appeared before the tone (CS) c. Conditioning seldom occurs when CS comes after the UCS d. Classical conditioning is biologically adaptive: Pavlov’s tone signals an important biological event-the arrival of food e. If the food or bad event had already occurred, the CS would not likely signal anything significant f. Conditioning helps and animal survive and reproduce; prepare for good and bad events g. In humans, stimulus associated with sexual pleasure, can become CS for sexual arousal h. Associations, even those not consciously noticed, can give rise to attitudes ii. Extinction a. Diminishing response that occurs when the CS no longer signals an impending UCS b. Ex: when Pavlov sounded the tone again and again without presenting food, the dogs salivated less c. Ex: After breaking up with girlfriend, one still stops pairing CS of smell of onion breath with kissing (US) iii. Spontaneous recovery a. Reappearance of a weakened CR after a rest pause: suggests that extinction suppresses the CR but does not eliminate it b. Ex: if Pavlov allowed several hours to elapse before sounding the tone again, the salivation to the tone would reappear spontaneously c. Ex: Occasionally, smelling onion breath still awakens a small version of emotional response iv. Generalization a. Tendency to respond to stimuli similar to the CS b. Pavlov and his students noticed that a dog conditioned to the sound of one tone also responded somewhat to the sound of a different tone never paired with food c. Generalization can be adaptive: toddlers fear moving cars and respond similarly to trucks, motorcycles, etc. d. Shown an angry face on a computer screen, abused children’s brain-wave responses are dramatically stronger and longer lasting e. Stimuli that are similar to naturally disgusting or appealing object will, by association, evoke some disgust or liking f. People’s emotional reactions to one stimulus generalize to similar stimuli v. Discrimination a. Learned ability to distinguish between a conditioned stimulus and other irrelevant stimuli b. Has survival value, because slight different stimuli are at times followed by vastly different consequences c. Pavlov’s dogs also learned to respond to the sound of a particular tone only d. Pavlov’s and Watson’s disdain for “mentalistic” concepts has given way to a growing realization that they underestimated the importance of cognitive processes and biological constraints D. Updating Pavlov’s Understandings i. Cognitive processes a. Early behaviorists believed that learned behaviors of various organisms could be reduced to mindless mechanisms, therefore, presumption of cognition seemed unnecessary b. Robert Rescorla and Allan Wagner argued that when two significant events occur closely together in time, an animal learns the predictability of the second event: if tone always precedes shock, and light sometimes accompanies tone, rats will fear tone not light c. The more predictable the association the stronger the CR d. Expectancy: awareness of how likely it is that the UCS will occur e. Conditioning occurs best when the CS and UCS have just the sort of relationship that would lead a scientist to conclude that the CS causes the UCS f. Classical conditioning treatments that ignore cognition often have limited success ii. Biological predispositions a. Pavlov and Watson believed the basic laws of learning were similar in all animals b. An animal’s capacity for conditioning is constrained by its biology; biological predispositions of each species dispose it to learn the particular associations that enhance its survival c. Garcia and Robert Koelling noticed that rats began to avoid drinking the water from the plastic bottles in radiation chambers d. Garcia and Koelling gave rats a particular taste, sight, or sound and later gave them radiation or drugs that led to nausea and vomiting a. Even if sickened as late as several hours after tasting a particular novel flavor, the rats thereafter avoided that flavor b. Sickened rats developed aversions to the tastes but not the sights or sounds c. This contradicted the behaviorists’ idea that any perceivable stimulus could serve as a CS e. Conditioning is even speedier, stronger, and more durable when the CS is “ecologically relevant” f. Birds, which hunt by sight, appear biologically primed to develop aversions to the sight of tainted food g. Humans, too, seem biologically prepared to learn some things rather than others h. These cases support Darwin’s principle that natural selection favors traits that aid survival i. Birds, which hunt by sight, appear biologically primed to develop aversions to the sight of tainted food j. Nature prepares the members of each species to learn those things crucial to their survival k. Experiments revealed that conditioned taste aversion could successfully prevent baboons from riding African gardens, raccoons from attacking chickens, and ravens and crows from feeding on crane eggs l. Learning enables animals to adapt to their environments: discovery of biological constraints on learning affirms this m. Animals are generally predisposed to associate a CS with a UCS that follows predictably and immediately n. Adaptation also helps explain exceptions such as the taste-aversion finding E. Pavlov’s Legacy i. Classical conditioning is a basic form of learning ii. Many other responses to many other stimuli can be classically conditioned in many other organisms iii. Classical conditioning is one way that virtually all organisms learn to adapt to their environment iv. Pavlov showed us how a process such as learning can be studied objectively, by isolating elementary blocks of complex behaviors and studying them with objective laboratory procedures v. Applications of classical conditioning a. Rug counselors advise addicts to steer clear of settings associated with the euphoria of previous drug use b. Counselors sometimes provide people who abuse alcohol with experiences that may reverse their positive associations with alcohol c. Works on the body’s disease-fighting immune system d. Provided a basis for John Watson’s idea that human emotions and behavior, though biologically influenced, are mainly a bundle of condtitioned responses e. “Little Albert” feared loud noises but not white rats: Watson and Rayner conditioned a fear of rats: Albert generalized this fear to rabbits, dogs, and sealskin coats f. Watson used his knowledge of associative learning to conceive many successful campaigns g. One patient who feared elevators for 30 years, forced himself to enter 20 elevators a day for 10 days, and his fear nearly vanished F. Close-Up: i. Her fear (CR) was most powerfully associated with particular locations and people (CS), but it generalized to other places and people ii. Rape victim fears apartment, town, darkness: fear is subsiding after eleven years III. Operant Conditioning A. Operant conditioning: association of behaviors with their consequences: more likely to repeat rewarded, reinforced behaviors and less likely to repeat punished behaviors B. Difference between classical and operant: classical conditioning forms an association between stimuli and involves respondent behavior: behavior that occurs as a automatic response to some stimulus; operant conditioning involves operant behavior: the act operates on the environment ot produce rewarding or punishing stimuli C. Skinner’s Experiments i. Law of effect: rewarded behavior is likely to recur ii. Skinner developed a “Behavioral technology” that revealed principles of behavior control iii. Enabled him to teach pigeons such unpigeonlike behaviors as playing ping-pong, and keep a missile on course by pecking at a target on a screen iv. Designed an operant chamber/Skinner box: soundproof, with a bar or key that an animal presses or pecks to release a reward of food or water, and a device that records these responses v. Shaping, a procedure in which reinforcers, such as food, gradually guide an animal’s actions toward a desired behavior a. After observing how the animal naturally behaves before training, you would build on its existing behaviors b. To condition hungry rat to press a bar you build on existing behaviors by using successive approximations: reward responses that are ever-closer to the final desired behaviors and ignore all other responses c. By making rewards contingent on desired behaviors, researchers and animal trainers gradually shape complex behaviors d. By shaping nonverbal organisms to discriminate between stimuli, a psychologist can also determine what they perceive e. Experiments show that some animals are remarkably capable of forming concepts; they demonstrate this by discriminating between classes of events or objects f. If an experimenter reinforces a pigeon for pecking after seeing a human face (discriminative stimulus), but not after seeing other images, the pigeon will learn to recognize human faces g. In shaping procedure the trainer builds on the individual’s existing behaviors by expecting and immediately rewarding successively closer approximations of a desired behavior. h. In everyday life we may unintentionally continually reward and shape the behavior of others vi. Principles of reinforcement a. Reinforcement: any event that increases the frequency of a preceding response, not necessarily a reward; any consequence that strengthens behavior b. Positive reinforcer may be a tangible reward c. Two kinds of reinforcement: positive: strengthens a response by presenting a typically pleasurable stimulus after a response and negative: strengthens a response by reducing or removing an aversive stimulus. d. Negative reinforcement is not punishment; rather, it removes a punishing aversive event e. Primary reinforcers-innately satisfying f. Conditioned reinforcers/secondary reinforcers: are learned: get their power through association with primary reinforcers (if rat in skinner box learns that a light reliably signals that food is coming, the rat will work to turn on the light: light becomes a secondary reinforcer) g. Humans respond to reinforcers that are greatly delayed h. To function effectively we must learn to postpone immediate rewards for greater longterm rewards i. To our detriment, small but immediate consequences are sometimes more alluring than big but delayed consequences j. Big step to maturity is learning to delay gratification to control impulse in order to achieve more valued rewards k. Continuous reinforcement: desired response is reinforced every time it occurs: learning occurs rapidly: extinction works rapidly: not provided in real life l. Partial/intermittent reinforcement: responses sometimes reinforced and sometimes not: initial learning slower (continuous reinforcement preferable until a behavior is learned): produces greater persistence and greater resistance to extinction m. With intermittent reinforcement, hope springs eternal vii. 4 Schedule of Partial Reinforcement a. Fixed-ratio schedules: behavior reinforced after set number of responses: piecework: often found tiring b. Variable-ratio schedules: provide reinforcers after an unpredictable number of responses: commission: high rates of responding because reinforcers increase as the number of responses increases c. Fixed-interval schedules: reinforce the first response after a fixed time period: salary: produces choppy stop-start pattern rather than a steady rate of response d. Variable-interval schedules: reinforce the first response after varying time intervals: random: tend to produce slow, steady, long-lasting responding e. Animal behaviors differ, yet Skinner contended that these reinforcement principles of operant conditioning are universal D. Punishment i. Effect opposite to that of reinforcement ii. Decreases frequency of preceding behavior usually by administering an undesirable consequence or withdrawing a desirable one iii. Swift and sure punishers can powerfully restrain unwanted behavior iv. Some punishments, though unintentional, are nevertheless quite effective: A dog that has learned to come running at the sound of the electric can opener will stop coming if its master starts running the machine to attract the dog and banish it to the basement v. Problem with human punishment studies, which often find that spanked children are at increased risk for aggression, depression, and low self-esteem vi. Physical punishment has drawbacks; punished behavior not lost only suppressed; temporary suppression may negatively reinforce the parents’ punishing behavior; may increase aggressiveness by demonstrating that aggression is a way to cope with problems vii. If punishment is avoidable, the punished behavior may reappear in safe settings, viii. The child may simply learn discrimination: different places mean different rules ix. Physical punishment may increase aggressiveness by demonstrating that aggression is a way to cope with problems x. Punishment can create fear xi. When punishments are unpredictable and inescapable, both animals and people may develop the sense that events are beyond their control; feel helpless and depressed xii. Even though punishment suppresses unwanted behavior, it often does not guide one toward more desirable behavior xiii. Punishment combined with reinforcement is usually more effective than punishment alone xiv. Parents of delinquent youth often lack this awareness of how to reinforce desirable behavior without screaming or hitting; training programs are available xv. Psychologists now favor an emphasis on reinforcement E. Updating Skinner’s Understanding i. Skinner resisted the growing belief that cognitive processes have a necessary place in the science of psychology and even in our understanding of conditioning ii. Cognitive processes might be at work in operant learning iii. Evidence of cognitive process has come from studying rats in mazes: develop a cognitive map, a mental representation of the environment: occurs even when passively carried through the maze in a wire basket iv. The animals behave as if they expected that repeating the response would soon produce the reward v. Cognitive map: a mental representation of the layout of one’s environment; e.g. maze vi. Rats exploring a maze develop a cognitive map; when an experimenter then places a reward in the maze’s goal box, the rats very quickly perform as well as rats that been reinforced with food for running the maze vii. Latent learning: learning that becomes apparent only when there is some incentive to demonstrate it viii. There is more to learning than associating a response with consequence, there is cognition ix. Learning can occur without reinforcement or punishment x. Unnecessary rewards sometimes carry hidden costs xi. Promising children a reward for a task they already enjoy can backfire. People who begin to see the reward as their motive for an activity may lose their intrinsic interest in it: overjustification effect: an already justifiable activity becomes overjustified by the promise of a reward xii. Intrinsic motivation: desire to perform a behavior effectively and for its own sake, can be undermined by excessive rewards xiii. Extrinsic motivation: seeking external rewards and avoiding threatened punishment xiv. Person’s interest often survives when a reward is used neither to bribe nor to control but to signal a job well done xv. If a reward boosts feeling of competence after doing good work, enjoyment of task may increase xvi. Rewards rightly administered can motivate high performance and creativity. xvii. An animal’s natural predispositions constrain its capacity for operant conditioning xviii. Biological constraints predispose organisms to learn associations that are naturally adaptive xix. Biological predispositions were more important than had been supposed xx. “Misbehaviors” occur when animals revert to their biologically predisposed patterns F. Skinner’s Legacy i. Skinner believes to manage people effectively we should worry less about their illusions of freedom and dignity; recognizing that behavior is shaped by its consequences, we should administer rewards in ways that promote more desirable behavior ii. Skinner’s critics objected saying that he dehumanized people by neglecting their personal freedom and by seeking to control their actions iii. At School a. Skinner and others advocated the use of teaching machines and textbooks that would shape learning in small steps and provide immediate reinforcement for correct responses b. Teachers should pace the material according to each students’ rate of learning and provide prompt feedback with positive reinforcement to both slow and fast learners c. Students must be told immediately whether what they do is right or wrong and, when right, they must be directed to the step to be taken next d. Computers can pace the material according to each student, keeping flawless records for the supervising teacher iv. In Sports a. Reinforcement principles can also enhance athletic abilities: key is to shape behavior, by first reinforcing small successes and then gradually increasing the challenge b. Compared with children taught by convention methods, those trained by this behavioral method show, in both testing and game situations, faster improvement in their skill v. At Work a. Business managers have capitalized on psychological research: many companies now enable their employees to share profits and to participate in company ownership; when workers’ productivity boosts rewards for everyone, their motivation, morale, and cooperative spirit often increase b. Reinforcement for a job well done is especially effective in boosting productivity when the desired performance is well-defined and achievable c. It is wise to make the reinforcement immediate d. Rewards need not be material, nor should they be substantial vi. At Home a. Many economists and psychologists believe people’s spending behavior is controlled by its consequences (its costs and benefits) b. In homes immediate consequences most effectively influence behavior c. When parents cave in to protests or defiance, they reinforce such behaviors d. Give children attention and other reinforcers when they are behaving well; target a specific behavior e. Ignore whining f. When children misbehave or are defiant, do not yell or hit them g. Can be applied to ourselves: state your goal, monitor yourself, reinforce the desired behavior, reduce the incentives gradually vii. Contrasting Classical and Operant Conditioning a. Both are forms of associative learning and both involve acquisition, extinction, spontaneous recovery, generalization, and discrimination b. Through classical conditioning, an organism associates different stimuli that it does not control and responds automatically c. Through operant conditioning, an organism associates its operant behaviors with their consequences d. Both are influenced by cognitive processes and biological predispositions IV. Learning by Observation A. Observational learning: we observe and imitate others B. Modeling: process of observing and imitating a specific behavior C. We can glimpse the roots of observational learning in other species D. Imitation is all the more striking in humans: so many ideas, fashions, and habits travel by imitation that these transmitted cultural elements now have a name: memes E. Mirror neurons: in frontal lobe area adjacent to the brain’s motor cortex, provide a neural basis for observational learning; may also serve in human language, and give rise to children’s empathy and to their theory of mind F. PET scans reveal that humans have mirror neurons in this brain area G. Imitation of models shapes children’s development H. Bandura’s experiments: i. Albert Bandura: pioneering researcher of observational learning ii. Child imitates aggression towards Bobo doll, at a time of aggression, after having seen the behavior in an adult iii. Observing the adult model beating up the doll lowered their inhibitions iv. Part of whether we will imitate a model is reinforcements and punishments v. By looking we learn to anticipate a behavior’s consequences vi. Especially likely to imitate those we perceive as similar to ourselves, as successful, or as admirable I. Applications of Observational Learning i. Antisocial models, may have antisocial effects ii. By watching TV, children may learn that physical intimidation is an effective way to control others, that free and easy sex brings pleasure without consequences, or that men are supposed to be tough and women gentle iii. Lessons we learn as children are not easily unlearned as adults, and they are sometimes visited on future generations iv. Intergenerational transmission of abuse could be genetic v. Prosocial: positive, constructive, helpful behavior, can have prosocial effects; people who exemplify nonviolent, helpful behavior can prompt similar behavior in others vi. Parents are powerful models, observational learning of morality begins early vii. Models are most effective when their actions and words are consistent viii. When exposed to a hypocrite, children tend to imitate the hypocrisy by doing what the model did and saying what the model said ix. Wherever television exists it becomes the source of much observational learning x. Most people have access to televisions and a major portion of their life watching it xi. U.S. network programs have offered about 3 violent acts per hour during prime time, and 18 per hour during children’s Saturday morning programs; real world-87% of crimes are nonviolent on television,13% of crimes are nonviolent xii. Television viewers are learning about life from a rather peculiar storyteller, one who reflects the culture’s mythology but not its reality xiii. In a study, 6 in 10 shows featured violence, that 74% of violence went unpunished, that 58% did not show the victims’ pain, and that nearly half the inciedents involved justified violence and nearly half involved an attractive perpetrator xiv. Correlational studies do link violence-viewing with violent behavior: more hours spent watching violent programs the more at risk they are for aggression and crime as teens and adults: increased homicide rates in US, Canada, and South Africa xv. These studies do not prove that viewing violence causes aggression xvi. Experiments show that violence shows can to an extent cause more cruel behavior xvii. The violence effect seems to stem from a combination of factors including imitation xviii. Prolonged exposure to violence also desensitizes viewers: watching cruelty fosters indifference