The role of the hippocampus in passive and active spatial learning.

Rats with lesions of the hippocampus or sham lesions were required in four experiments to escape from a square swimming pool by finding a submerged platform. Experiments 1 and 2 commenced with passive training in which rats were repeatedly placed on the platform in one corner-the correct corner-of a pool with distinctive walls. A test trial then revealed a strong preference for the correct corner in the sham but not the hippocampal group. Subsequent active training of being required to swim to the platform resulted in both groups acquiring a preference for the correct corner in the two experiments. In Experiments 3 and 4, rats were required to solve a discrimination between different panels pasted to the walls of the pool, by swimming to the middle of a correct panel. Hippocampal lesions prevented a discrimination being formed between panels of different lengths (Experiment 3), but not between panels showing lines of different orientations (Experiment 4); rats with sham lesions mastered both problems. It is suggested that an intact hippocampus is necessary for the formation of stimulus-goal associations that permit successful passive spatial leaning. It is further suggested that an intact hippocampus is not necessary for the formation of stimulus-response associations, except when they involve information about length or distance.

The role of local, distal, and global information in latent spatial learning.

In 4 experiments that investigated latent spatial learning, rats were repeatedly placed on a submerged platform in a corner of a square swimming pool with walls of different brightness. When they were subsequently released into the pool for a test trial in the absence of the platform, they spent the majority of time in the corner used for placement training-the correct corner. This effect was observed in Experiment 1, even when the test trial took place in a transformed version of the training arena. Experiments 2 and 3 indicated that the correct corner was identified by local cues based on the walls creating the corner. Experiment 4 demonstrated that distal cues created by the two walls that did not surround the platform during placement training could also be used to identify the correct corner. There was no evidence of learning about the relationship between global cues provided by the entire arena and the goal. The absence of the opportunity to develop instrumental, stimulus-response associations during placement training indicates that stimulus-stimulus associations acquired during this training were sufficient to guide rats to the platform when they were eventually released into the pool.

Response-Outcome versus Outcome-Response Associations in Pavlovian-to-Instrumental Transfer: Effects of Instrumental Training Context.

One experiment with rats used Pavlovian-to-instrumental transfer (PIT) tests to explore potential competitive interactions between Pavlovian and instrumental processes during instrumental learning. Two instrumental response-outcome relations (e.g., left lever - grain pellets, right lever - sucrose pellets) were first trained in distinct contexts for one group of rats (Group Differential) or in each of two contexts for a second group (Group Non-Differential). Both of these groups then received training with two Pavlovian stimulus-outcome relations in a third experimental context. Selective PIT tests conducted in both the Pavlovian and instrumental contexts revealed greater selective PIT in Group Non-Differential than in Group Differential subjects. This result is discussed in terms of the roles played by context-outcome, response-outcome, and outcome-response associations during instrumental learning. The results further help us understand the nature of Pavlovian-instrumental interactions in specific PIT tasks.

Latent spatial learning in an environment with a distinctive shape.

Four experiments were conducted with rats in order to determine whether being placed on a platform in one corner of a rectangular swimming pool results in latent spatial learning. Rats in Experiments 1-3 received four trials a day of being placed on the platform. During a subsequent test trial, in which they were released into the pool without the platform, the rats exhibited a preference for swimming in the correct corners of the pool (those with the same geometric properties as the corner containing the platform during training), than the two remaining, incorrect corners. This effect was seen when the interval between the final placement trial and the test trial was as much as 24 hr (Experiment 2) and after varying numbers of sessions of placement training (Experiment 3). Experiment 4 revealed that when the test took place in a kite-shaped arena, after placement training in a rectangle, a stronger preference was shown for the corner that was geometrically equivalent to the correct rather than the incorrect corners in the rectangle. The placement treatment is said to result in latent spatial learning based on the development of S-S associations.