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Riflesso Condizionato (Pavlov)

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maxpower1th
view post Posted on 18/3/2013, 17:13




How Dog Training Works

Learning Theory
Dog training typically centers on operant conditioning. The first scientist to define this concept was B.F. Skinner, who studied the work of Russian physiologist Dr. Ivan Pavlov on animal behavior. In Pavlov's groundbreaking study, dogs learned that a stimulus (in this case, a bell) meant they were about to be fed. Starting with two things that are naturally paired -- salivating and being fed -- Pavlov added a third component by ringing a bell before feeding. After a few trials, the dogs learned to associate the bell with being fed and would react by salivating at the sound of the bell in anticipation of their food but without any food present.

Since dogs naturally begin salivating when offered food, food is an unconditioned stimulus. No conditioning or special training is necessary to cause the dog to salivate, which is an unconditioned response. In contrast, a ringing bell does not normally cause dogs to salivate; they will do so only if they have been conditioned to associate a bell with being fed. Therefore, the bell is a conditioned stimulus. The dog's new reaction is a reflex to the stimulus and is a conditioned response.

Many of us see this today with our own dogs when they break into a frenzy of barking at the sound of the doorbell, sometimes even a doorbell on television. In this case, the dog has been conditioned to associate the stimulus of the bell with the imminent arrival of a stranger.

When we see flashing lights or hear a siren behind us while driving, we may reflexively tense up and our heart rate may increase. We have been conditioned to associate the sound of sirens with the unpleasant and stressful experience of getting a ticket. This is classical conditioning. Both animals and people can learn to relate a pair of events and respond to the first in anticipation of the second. This type of learning is passive and involuntary; it occurs without the learner doing anything and often without awareness.

While Pavlov's work dealt with a reflexive reaction to a conditioned stimulus, Skinner became interested in creating a specific behavioral reaction to a stimulus by adding a reinforcer. A reinforcer can be either a reward or a punisher. A reward is anything that increases the frequency of an action; a punisher is anything that decreases its frequency.

When we are rewarded for a certain behavior, we are likely to repeat that behavior. When we are punished for a certain behavior we are likely to stop. This type of learning is active and voluntary; it depends on the actions of the learner.

Because the definition of a reinforcer is based on its effectiveness, it's important to remember that a reward for one person may not be meaningful, and thus not a reward, for another. Similarly, what is a reward in one context may not be somewhere else.

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Skinner showed that both animals and people would perform certain behaviors for a reward. In his experiments with rats and pigeons, Skinner showed how animals could learn to press a lever to get a food reward. When the animals were first introduced to the test box they moved around randomly. When they accidentally depressed the lever, a food pellet was dispensed. They quickly learned to depress the lever on purpose to get a pellet. He also shaped behaviors that are more complicated by reinforcing them step by step. Skinner called his approach "operant conditioning" because the animal's behavior actually operated on the environment (pressing the lever) in response to the anticipated outcome (getting a food reward).

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Rewarding to encourage good behavior and punishing to discourage bad is something most of us do instinctively; it's common sense. Operant conditioning had a long history in animal training even before it was ever defined. Colonel Konrad Most, who published "Training Dogs: A Manual" in 1910, was using many of the same principles that Skinner studied, decades before he described them. Col. Most's training methods seem somewhat harsh by today's standards, but he is considered by many to be the father of modern dog training. Most, and other trainers used both rewards and punishers to shape and reinforce desired behavior.

Next, we'll look at how reinforcers are used in animal training.



Reinforcers

Reinforcers can involve either the addition of a new element or the removal of an element currently present. The terminology for this is a little confusing, but adding something is referred to as "positive," though not necessarily in the sense of "happy" or "good." "Negative," in this case, is the removal of something, and doesn't necessarily mean "bad." Therefore, both rewards and punishers can be either positive or negative.

Giving a parrot a piece of fruit for waving its foot is an addition of something good (a positive reward); a horse moving faster to stop the pressure of spurs is the ending of something bad (negative reward). Even though "negative reward" sounds like an oxymoron, the removal of something bad is a kind of reward.

There are many ways to teach a dog to sit using a reinforcer. The trainer may push or lure the dog into a sitting position, or he may simply wait until the dog sits naturally on its own. Once the dog sits, the trainer may offer a positive reward such as verbal praise ("good boy!"), tactile praise (a pat on the head), a favorite toy, or a treat. Some trainers use negative rewards like electronic collars to administer a mild shock to the dog, which stops as soon as he sits. The dog learns he can eliminate the shock by sitting. For ethical reasons, many people frown on this. However, it follows the same principles of operant conditioning. In every case, the dog will learn that when he hears the command "sit" and he sits, he will get a reward.

Reinforcers can be almost anything as long as they are meaningful to the dog. One dog may think treats are more valuable than toys, while another may feel the opposite. It doesn't really matter what the reinforcer is, but for practical reasons, some reinforcers are easier to work with than others. Also, the same reinforcer doesn't have to be used every time or in every situation. Some tasks may require a more valuable reinforcer than others. As PetSmart obedience trainer Dan O'Leary puts it, "you would probably step over a chair if I offered you a dollar to do it. But you probably wouldn't wash and wax my car for a dollar." Similarly, your dog may work for one type of reward in the relative calm of your home but may need something more desirable to maintain focus in class.

We'll look at how trainers developed markers, or cues, to train animals other than dogs
 
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maxpower1th
view post Posted on 18/3/2013, 17:33




Riflesso condizionato

Il riflesso condizionato o riflesso pavloviano, dal nome dello scienziato russo Ivan Pavlov che elaborò il concetto agli inizi del Novecento nell'ambito degli studi sul comportamento, è la risposta che il soggetto dà alla presentazione di uno stimolo condizionante.

Il riflesso condizionato è una reazione prodotta nell’animale in cattività da un elemento esterno, che l’animale si abitua ad associare ad un preciso stimolo (presentato subito dopo durante la fase di condizionamento; subito prima una volta effettuato il condizionamento). Il primo agente diventa perciò lo stimolo chiave, ciò che attiva il riflesso condizionato.



Esperimento di Pavlov

Uno dei cani di Pavlov con impianto di cannula per misurare la salivazione (Pavlov Museum, Ryazan, Russia, 2005)L'esperimento classico di Pavlov si propone la dimostrazione del riflesso condizionato, cioè con uno stimolo naturale si è in grado di provocare il verificarsi di un determinato evento (risposta). Gli organismi (animali ed umani) imparano ad associare uno stimolo con un altro. Centrali per il condizionamento classico sono i riflessi, ovvero risposte non apprese e non controllabili, come la salivazione, la contrazione pupillare, la chiusura degli occhi.

Associando per un certo numero di volte la presentazione di carne ad un cane con un suono di campanello, alla fine il solo suono del campanello determinerà la salivazione nel cane. La salivazione è perciò indotta nel cane da un riflesso condizionato provocato artificialmente.

Pavlov approntò la fase di condizionamento: dava da mangiare al cane ogni qualvolta si presentava il suono del campanello.

Dopo varie ripetizioni, lo stimolo del campanello si trasformava in stimolo condizionato capace di produrre da solo una risposta, questa volta condizionata, di salivazione.

Lo stimolo incondizionato è qualsiasi stimolo che naturalmente evoca un comportamento riflesso, ad esempio la salivazione in seguito alla vista/odore del cibo; risposta incondizionata è il comportamento riflesso, come ad esempio la salivazione, evocato da uno stimolo incondizionato; stimolo neutro è uno stimolo che non ha alcun significato per l'organismo (campanello). Quando è associato a uno stimolo incondizionato, lo stimolo neutro può diventare uno stimolo condizionato.

Gli esperimenti di Pavlov portarono all'utilizzo di questi cani per l'Armata Rossa ai tempi della Seconda Guerra Mondiale per distruggere i Panzer tedeschi. Venivano imbottiti di esplosivo e portati alla fame e addestrati a cercare cibo sotto i carri armati tedeschi (nei cingoli) e con questa tecnica furono distrutti circa 700 Panzer, ma si rivelò più che altro fallimentare, dato che era una tecnica disperata.



Fonte: http://it.wikipedia.org/wiki/Riflesso_condizionato
 
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1 replies since 18/3/2013, 17:11   193 views
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