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Learning is the alteration of behavior as a result of experience. When an organism is observed to change its behavior, it is said to learn. Many theories have been formulated by psychologists to explain the process of learning. Early in the twentieth century, learning was primarily described through behaviorist principles that included associative, or conditioned response. Associative learning is the ability of an animal to connect a previously irrelevant stimulus with a particular response. One form of associative learning—classical conditioning—is based on the pairing of two stimuli. Through an association with an unconditioned stimulus, a conditioned stimulus eventually elicits a conditioned response, even when the unconditioned stimulus is absent. The earliest and most well-known documentation of associative learning was demonstrated by Ivan Pavlov, who conditioned dogs to salivate at the sound of a bell. In operant conditioning, a response is learned because it leads to a particular consequence (reinforcement), and it is strengthened each time it is reinforced. Without practice any learned behavior is likely to cease, however, repetition alone does not ensure learning; eventually it produces fatigue, boredom, and suppresses responses. Positive reinforcement strengthens a response if it is presented afterwards, while negative reinforcement strengthens it by being withheld. Generally, positive reinforcement is the most reliable and produces the best results. In many cases once the pattern of behavior has been established, it may be sustained by partial reinforcement, which is provided only after selected responses.

In contrast to classical and operant conditioning, which describe learning in terms of observable behavior, other theories focus on learning derived from motivation, memory, and cognition. Wolfgang Köhler, a founder of the Gestalt school of psychology, observed the importance of cognition in the learning process when he studied the behavior of chimpanzees. In his experimentation, Köhler concluded that insight was key in the problem-solving conducted by chimpanzees. The animals did not just stumble upon solutions through trial and error, but rather they demonstrated a holistic understanding of problems that they solved through moments of revelation. In the 1920s, Edward Tolman illustrated how learning can involve knowledge without observable performance. The performance of rats who negotiated the same maze on consecutive days without reward improved drastically after the introduction of a goal box with food, indicating that they had developed cognitive maps of the maze prior to the reward although it had not been observed in their behavior.

In the 1930s, Clark L. Hull and Kenneth W. Spence introduced the drive-reduction theory. Based on the tendency of an organism to maintain balance by adjusting physiological responses, the drive-reduction theory postulated that motivation is an intervening factor in times of imbalance. Imbalances create need, which in turn create drives; both encourage action in order to reduce the drive and meet the need. According to drive-reduction theory, the association of stimulus and response in classical and operant conditioning only results in learning if accompanied by drive reduction.

Perceptual learning theories postulate that an or ganism's readiness to learn is of primary importance to its survival, and this readiness depends largely on its perceptual skills. Perceptual skills are intimately involved in producing more effective responses to stimuli. In the laboratory, perceptual learning has been tested and measured by observing the effects of practice on perceptual abilities. Subjects are given various auditory, olfactory, and visual acuity tests. With practice, subjects improve their scores, indicating that perceptual abilities are not permanent but are modifiable by learning. In studies of animal behavior, the term perceptual learning is sometimes used to refer to those instances in which an animal learns to identify a complex set of stimuli that can be used to guide subsequent behavior. Examples of such perceptual learning include imitation and observational learning, song learning in birds, and imprinting in newborn birds and mammals. Imprinting occurs only during the first 30 or so hours of life. It is a form of learning in which a very young animal fixes its attention on the first object with which it has visual, auditory, or tactile experience and thereafter follows that object.

Observational learning, also known as modeling or imitation, proposes that learning occurs as a result of observation and consequence. Behavior is learned through imitation, however behavior that is rewarded is more readily imitated than behavior that is punished. Termed vicarious conditioning, this type of learning is present when there is attention to the behavior, retention and the ability to reproduce the behavior, and motivation for the learning to occur.

Current research on learning is highly influenced by computer technology, both in the areas of computer-assisted learning and in the attempt to further understand the neurological processes associated with learning by developing computer-based neural networks that simulate different types of learning.

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