Animal training is the act of teaching animals specific responses to specific conditions or stimuli. Training may be for purposes such as companionship, detection, protection, and entertainment. The type of training an animal receives will vary depending on the training method used, and the purpose for training the animal. For example, a seeing eye dog will be trained to achieve a different goal than a wild animal in a circus. In some countries animal trainer certification bodies exist. They do not share consistent goals or requirements; they do not prevent someone from practicing as an animal trainer nor using the title. Similarly, the United States does not require animal trainers to have any specific certification. An animal trainer should consider the natural behaviors of the animal and aim to modify behaviors through a basic system of reward and punishment. Methods The behavioral approach Principles During training, an animal trainer can administer one of four potential consequences for a given behavior: Positive reinforcement Occurs when an animal's behavior is followed by a stimulus that increases occurrences of the behavior in the future. Negative reinforcement Occurs when a behavior is followed by the removal of an aversive stimulus, which causes the occurrences of the behavior to increase in the future. Positive punishment Occurs when a behavior is followed by the addition of an aversive stimulus. This causes a decrease in occurrences of behavior in the future. Negative punishment Occurs when a behavior is followed by the removal of a stimulus. As a result, the occurrences of the behavior decrease in the future. Behavior analysts emphasize the use of positive reinforcement for increasing desirable behaviors and negative punishment for decreasing undesirable behaviors. If punishment is going to be used to decrease an undesirable behavior, the animal must be able to receive positive reinforcement for an alternative behavior. Establishing new behavior Reinforcement should be provided according to a predetermined schedule. Such a schedule of reinforcement specifies whether all responses or only some are reinforced and includes the following: Variable ratio A reinforcer delivery occurs after a set number of responses, but that number varies around an average number. Fixed ratio A specific number of responses occur before a reinforcer is delivered. Variable interval The first response that is emitted after a set but variable amount of time has elapsed is reinforced. Fixed interval The first response that is emitted after a set time has