Latent learning is a form of learning that is not immediately expressed in an overt response; it occurs without any obvious reinforcement of the behavior or associations that are learned. Interest in latent learning arose largely because the phenomenon seemed to conflict with the widely held view that reinforcement was necessary for learning to occur.
In a classic study by Edward C. Tolman, three groups of rats were placed in mazes and their behavior observed each day for more than two weeks. The rats in Group 1 always found food at the end of the maze; the rats in Group 2 never found food; and the rats in Group 3 found no food for 10 days, but then received food on the eleventh. The Group 1 rats quickly learned to rush to the end of the maze; Group 2 rats wandered in the maze but did not preferentially go to the end. Group 3 acted the same as the Group 2 rats until food was introduced on Day 11; then they quickly learned to run to the end of the maze and did as well as the Group 1 rats by the next day. This showed that the Group 3 rats had learned about the organisation of the maze, but without the reinforcement of food. Until this study, it was largely believed that reinforcement was necessary for animals to learn such tasks.  Other experiments showed that latent learning can happen in shorter durations of time, e.g. 3-7 days. Among other early studies, it was also found that animals allowed to explore the maze and then detained for one minute in the empty goal box learned the maze much more rapidly than groups not given such goal orientation.
In 1949, John Seward conducted studies in which rats were placed in a T-maze with one arm coloured white and the other black. One group of rats had 30 mins to explore this maze with no food present, and the rats were not removed as soon as they had reached the end of an arm. Seward then placed food in one of the two arms. Rats in this exploratory group learned to go down the rewarded arm much faster than another group of rats that had not previously explored the maze.
In 1952, Bendig investigated latent learning using a Morris water maze. In this type of maze, there are escape platforms hidden just below the surface of water in a large tank. The animal is forced to swim until it reaches (and memorises) where the platforms are. Bendig required rats to escape a water maze while satiated for food, with food located on one of the escape platforms. Upon being returned to the maze while food deprived, the rats learned where the food was located at a rate that increased with the number of pre-exposures given the rat in the training phase. This indicated varying levels of latent learning.
Most early studies of latent learning were conducted with rats, but a study by Stevenson in 1954 explored this method of learning in children. Stevenson required children to explore a series of objects to find a key, and then he determined the knowledge the children had about various non-key objects in the set-up. The children found non-key objects faster if they had previously seen them, indicating they were using latent learning. Their ability to learn in this way increased as they became older.
In 1982, Wirsig and co-researchers used the taste of sodium chloride to explore which parts of the brain are necessary for latent learning in rats. Decorticate rats were just as able as normal rats to accomplish the latent learning task.
More recent studies
An experiment with infants explored latent learning at an early age. Three-month-olds were exposed to two different hand puppets simultaneously. The infants were then periodically presented with one of the puppets until they reached 6-months of age, at which point a target behavior was demonstrated on the first puppet. Finally, the infants were presented with the alternative puppet and performed the target behavior on that puppet at a higher rate than the control group which had not seen the two puppets paired. This suggests that the pre-exposed infants had formed an association between the puppets without obvious reinforcement.
Another experiment suggested that not all potential associations are easily formed by latent learning. Human participants undeprived of caffeine were given a novel caffeinated drink for four days and then were given the drink on a caffeine-deprived fifth day. These participants did not show an increased liking for the flavor upon being caffeine-deprived, while subjects who underwent the same procedure while deprived of caffeine every day showed an increased liking for the flavor each day. In this case, flavor quality as a function of caffeine did not seem to be acquired through latent learning.
There have been several investigations of the neural processes involved in latent learning. In one study, patients with medial temporal amnesia had particular difficulty with a latent learning task which required representational processing. Another study, conducted with mice, found intriguing evidence that the absence of a prion protein disrupts latent learning and other memory functions in the water maze latent learning task, while phencyclidine was found to impair latent learning in a water finding task.
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