Transcript Chap3
PSY 402 Theories of Learning Chapter 3 – Nuts and Bolts of Conditioning (Mechanisms of Classical Conditioning) Classical vs. Instrumental The modern view is that these two types of learning involve similar learning processes, but differ in the following ways. 1. 2. In Classical conditioning, two stimuli are associated with each other but in Instrumental conditioning, a stimulus and a response are associated. In Classical conditioning, the response is a reflex or involuntary action but in Instrumental conditioning, the response is a voluntary, freely emitted behavior. Pavlov’s Conditioned Reflex Conditioning -- a stimulus that initially produces no response can acquire the ability to produce one. Learning occurs through pairing in time and place of one stimulus with another stimulus that produces an involuntary response. Political Classical Conditioning Terminology of Conditioning Unconditioned stimulus (US or UCS) Elicits a reflexive response without learning. Unconditioned response (UR or UCR) The response that occurs with a US, typically a reflex, emotion or drug state Involuntary and automatic. More Terminology Neutral stimulus Conditioned stimulus (CS) A stimulus not capable of producing an unconditioned response (before learning). A previously neutral stimulus that has acquired the ability to evoke a response. Conditioned response (CR) The learned response, often similar to the UCR, an involuntary reflex, emotion or drug state. Prior to conditioning Neutral stimulus (tone) (Orientation to sound but no response) UCS (food powder in mouth) UCR (salivation) During Conditioning Neutral stimulus CS (tone) + UCS (food powder) CR (salivation) After conditioning CS (tone) CR (salivation) Conditioning Processes Stimulus generalization – stimuli like the CS become able to evoke the conditioned response. Extinction – if the UCS and CS are not paired, the CS loses its ability to produce a conditioned response. Spontaneous recovery – an extinguished CS briefly returns but quickly goes away again. What is Learned? Pavlov believed the association was between the two stimuli (tone and meat powder), not between the tone and salivation. Either is possible Stimulus substitution Conditioning Situations Sign-tracking (autoshaping) – animals must recognize signs of food (UCS) and respond (UCR). Pigeons pecking at key. UCR, not an operant response, because behavior is specific to the stimulus. Eyeblink conditioning UCR is rapid, CR is slow. Many trials are needed (100 pairings) 3.7 Autoshaping in pigeons (Part 1) 3.7 Results of autoshaping tests in pigeons (Part 2) 3.5 Design of eyeblink conditioning experiment in rabbits (Part 1) 3.5 Results of eyeblink conditioning experiment in rabbits (Part 2) Conditioned Emotional Responses Fear is an anticipatory pain response based on past experience. Fear is conditioned (becomes a CR) whenever a CS is associated with an aversive (painful or undesirable) event. Fear motivates two responses: Escape (when pain is present) Avoidance (when pain is imminent) Fear conditioning Avoidance is not a good measure of fear. Suppression of an operant behavior occurs with a feared stimulus. First – an operant behavior is learned. Second – a CS is paired with an aversive UCS. Third – the CS is presented in the operant chamber and the effect on operant responding is measured. 3.6 Conditioned suppression in rats (Part 1) Suppression Ratio During CS Suppression Ratio = During CS + Without CS The amount of time during and without the CS is equal. The more fear, the lower the suppression ratio. Ratios typically fall between 0 and .5 This will be on the midterm 3.6 Conditioned suppression in rats (Part 2) Flavor Aversion Learning Garcia – rats will not drink water with saccharin if they get ill after drinking. Significant avoidance occurs after just one trial. Human food aversions are related to illness (89%). Even if illness occurs hours later it is linked to the previous meal. Not cognitive – you can know the food is not to blame and still feel an aversion to it. Acquired Changes in Response Habituation – response to a repeated stimulus decreases with non-threat experience. Sensitization – response to a variety of stimuli increases with a single threat experience. Examples: Ingestional neophobia, fear of new food Rats orient less toward light, startle decreases Chicks are less frightened by shadows flying overhead with repeated exposure. Factors Affecting Conditioning Timing – how closely in time are the CS and UCS, and which occurs first. Novelty of the CS and UCS. Intensity (strength) of the CS and UCS. Consistency of the pairing between the CS and UCS. If one or the other appears alone then conditioning is weakened. Stimulus Presentation Paradigms Delayed conditioning – the CS onset precedes the UCS onset. Trace conditioning – the CS starts and ends before the UCS onset. Simultaneous conditioning – the CS and UCS occur together. Backward conditioning – the UCS starts and ends before the CS onset. These paradigms will be on the midterm 3.8 Different ways to present CS and US in time This works best The longer the gap (trace interval) the worse this works This isn’t as good as delayed This doesn’t work at all Massed vs Spaced Trials Better learning occurs when trials are spaced out over time (spaced), rather than bunched together (massed). Memory consolidation or rehearsal may be needed between trials. The ratio between the exposure to the CS and the time in-between is the important factor. If both are the same duration, learning is weaker. 3.9 Trial spacing in Pavlovian conditioning This works best This doesn’t work as well Importance of Novelty Preexposure to the CS (before it is paired with the UCS) reduces learning. The same thing happens with preexposure to the US (before it is paired with the CS). Called latent inhibition because it inhibits learning of the CS-UCS association. Called the US preexposure effect Other, more novel stimuli are more likely to become associated with the UCS. Stimulus Intensity (Strength) The stronger the US (UCS), the faster the learning and the stronger the association. The stronger the CS, the better the learning. Salience – how attention-getting the stimulus is in relation to other stimuli in the environment. The most salient CS becomes associated with the UCS. An overpowering CS may elicit a response of its own, preventing learning. Pseudo-conditioning Responses to the CS may occur due to the strength of the UCS, not learning. Once air has been puffed at the eye, blinking may occur in response to any stimulus that comes next, without any learning. Sensitization resulting from an intense UCS may cause the response to a CS to be increased, even when there is not greater learning. A control group lets you tell the difference. 3.10 Bernstein’s experiment on taste aversion learning Classical Conditioning Adaptation Organisms learn to recognize and respond selectively to the signals that are important in their environment. Cues associated with food evoke digestion: salivation, gastric juices, insulin secretion. Taste aversion learning – illness makes us avoid foods that were eaten just prior to feeling sick. Food preferences are associated with nutrients. Examples of Conditioning Popcorn at the movies. Fear of flying -- stronger with more turbulence (a stronger UCS). An antelope shying away from low tree branches. Nausea at the smell of alcohol after a hangover. Territoriality Environmental cues can become associated with sexual rival males in gourami fish. Pairing the light with the rival signaled the other fish to prepare so it was able to be more aggressive. Presenting the light without pairing it with the rival had no effect. Courtship behavior can also be conditioned, leading to more successful nestbuilding, etc. Fear Conditioning Freezing is a universal response to threat. Animals that freeze are less likely to be attacked. Fear is an anticipatory pain response. It occurs in response to stimuli that have been aversive in the past and motivates escape or avoidance behaviors. Fear also releases endorphins in rats who are confronted by the smell or sight of a cat. Conditioning and Addictions Drugs can be associated with environmental cues present when the drugs are taken. Instead of the drug response being conditioned, an opposite adaptive response is conditioned that lessens the drug’s effect. This is called drug tolerance. Taking a drug under novel circumstances can produce a drug overdose because the compensatory effect is not present (no cues). Sign Tracking (Auto-Shaping) Sign tracking occurs when a stimulus (cue) in the environment is associated with reward or punishment. The sign stimulus motivates approach or avoidance behavior because of what it signals. Negative sign tracking occurs when a sign motivates withdrawal instead of approach. Some signs signal safety because they mean a bad thing is less likely to occur. Extinction Associations are learned when they enhance survival, but conditioning decreases when the expected consequence no longer occurs. Extinction occurs with both instrumental and classical conditioning. Spontaneous recovery occurs after extinction has been learned, but a break in exposure to the stimulus occurs. After spontaneous recovery, extinction returns. Timing of Stimuli The strength of both instrumental and classical conditioning depends on the timing of events. Reward or punishment must immediately follow the emitted response in order to strongly affect behavior. Two stimuli must occur close together in time in order for them to be associated with each other. Size of the Stimuli The strength of both instrumental and classical conditioning also depends on the size of the stimuli. Larger rewards produce a stronger response than smaller ones. More intense stimuli are better signals and evoke greater conditioned responses. More fear, more saliva. Preparedness Affects Learning Both instrumental and classical conditioning are affected by preparedness (the innate nature of the organism). Flavor aversion learning is easier with taste cues than with visual cues, but not shock. Rooting behaviors interfere with learning for pigs trained to put a wooden coin in a “bank”. Some hamster behaviors are easier to learn. Humans Show Preparedness Humans show preparedness too, appropriate to our species. Nausea can be associated with tequila but not with friends or a shot glass. Snake and spider phobias may be especially prevalent due to preparedness. People associate shock with spiders or snakes more readily than with flowers or mushrooms.