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Learn Mem. 1995 May-Aug;2(3-4):107-32.

Remembering and forgetting as context discrimination.

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  • 1Department of Psychological Sciences, Purdue University, West Lafayette, Indiana 47907-1364, USA.


In 1929, H.C. Blodgett reported the results of a seminal maze learning experiment using rats. In that experiment, hungry rats ran in a complex maze but were not rewarded on reaching the goal box. Not surprisingly, the performance of the hungry rats did not improve over trials. However, with the introduction of reward, the error scores of the rats suddenly dropped to the level of the control rats that were rewarded from the outset. This finding indicates that the experimental group had learned the maze despite the absence of reward but that the learning was latent rather than manifest. With Blodgett's findings, the distinction between learning and performance became firmly established, if not as widely appreciated as it might be. Blodgett's (1929) early experimental finding of latent learning could well serve as a paradigm for the approach taken here. That is, we have emphasized the principle that a lack of performance does not necessarily indicate a lack of either learning or memory. This principle is much more than an empty admonition: We have shown it can have a firm theoretical basis, one that has been confirmed repeatedly by experiments cited throughout this paper. That is, it has been shown numerous times that a failure to perform either in a Pavlovian or instrumental learning task or to remember in an animal or human memory task under one set of conditions could be alleviated under another set of conditions. Forgetting was viewed here as a failure of performance resulting from the cues at test retrieving a memory other than the target memory or retrieving no memory at all. According to this view, memory involves discrimination learning. Essentially, memories are stored in the presence of an elaborate set of interoceptive and exteroceptive stimuli, a context. Whether at test the target memory is retrieved depends on how well the cues at test discriminate between the target memory and other memories. This approach suggests that forgetting does not occur: There is only a failure to perform because of a difference between the stimulus conditions prevailing at encoding and at test. It was demonstrated that this approach is at least as reasonable as that which suggests that true forgetting occurs, but certainly more useful. At least three advantages adhere to our view that memory is a discrimination problem. First, in almost numberless cases, it has been shown that failure of performance under one set of stimulus conditions can be alleviated under some other set of stimulus conditions. Second, the proposition that altered stimulus conditions are responsible for forgetting is one of wide generality. Thus, the altered stimulus conditions approach can serve as an explanation not only for various human memory findings but also for various animal memory and learning findings. Finally, and perhaps most importantly, the present approach provides investigators with a powerful and proven working hypothesis. It tells us not to accept failures of performance as indicating an absence of learning or a loss of memory but rather to seek conditions favorable to improving performance, a strategy that should lead to a better fundamental understanding of memory and learning. This position is obviously a type of optimality theory, of which evolutionary theory is one of the more outstanding examples. In optimality theory, any deviation from some ideal state or condition prompts the investigator to seek the reasons for deviation. This approach may prove as successful when applied to learning and memory as it has to other areas of science.

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