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.