(The first author of this post was Ken Malmberg.) About 50 years ago, Richard C. Atkinson and Richard M. Shiffrin published the results of several years of research in Human Memory: A Proposed System and its Control Processes. The recent special issue of Memory & Cognition calls attention to this anniversary and celebrates its contribution to cognitive science. There were two key advances that influenced the emerging field of cognitive psychology in profound ways: the mathematical formulation of cognitive processes and the interplay between rigorous theory and comprehensive data, which was rare at the time.
In addition to the lasting, general influences on cognitive psychology, Atkinson and Shiffrin chapter has had a particular influence on our understanding of human memory. The 100 pages of the chapter presented a general framework for understanding the complexities of human memory. The specific assumptions used to implement the framework were those suggested by or required to fit quantitative models to a variety of data from laboratory studies, and in a number of cases, new findings collected by these authors and their collaborators.
As prescient as it was, the early research left many issues incomplete, and of course did not deal with a large number of findings that have emerged in the years since. Thus, the model and framework have been extended and enlarged as time has passed, sometimes in publications by Shiffrin and his colleagues, and sometimes in publications by others. Of course diverse researchers have not always agreed on the best way to characterize memory or on how to interpret various findings, and many of the advances in memory theory and debates about the best ways to characterize memory processes have used the modal model as a starting point for developments.
Our contribution to the special issue (Malmberg, Raaijmakers, & Shiffrin, 2019), of course, could not touch on all the many issues and developments. Consider an example that was precluded from discussion by space limitations: Effects of memory testing.
Research into the nature of recognition memory was only just beginning when the chapter was published (Mandler, Pearlstone, & Koopmans, 1969). Initially, there was the notion that recognition decisions could be based on several factors but that a primary component would be the familiarity of the stimulus (Parks, 1966; Atkinson & Juola, 1974). There was a burst of scientific creativity and ingenuity in the 1980s to create a family of global-matching models to describe how the familiarity of the stimulus was obtained (Murdock, 1982; Gillund & Shiffrin, 1984; Hintzman, 1988; Humphreys, Bain, & Pike, 1989). The models differed, but they all assumed that the familiarity of the tested stimulus was positively related to the similarity of the retrieval cue to the traces stored during study, a similarity calculated via a global-matching process. Thus, increasing the amount of item information stored by increasing the number of massed and spaced repetitions improves recognition memory.
The global-matching mechanisms could not, however, account for a set of critical findings termed ‘list-strength’: In a mixed experimental list, some items are made stronger than others (by extra study time or repetitions). Control lists have equal strength items. In mixed lists, the presence of strong items slightly improved recognition memory but harmed free recall for the weaker items (Shiffrin, Ratcliff, & Clark, 1990).
These results led to a new wave of creativity and ingenuity that added Bayesian computational and decision processes to the global-matching approach (Glanzer, Adams, Iverson, & Kim, 1993; Shiffrin & Steyvers, 1997; Anderson et al., 1998; McClelland & Chappell, 1998). The key assumptions were that repeated item and context information about events often accumulates in the same trace, leading to the differentiation of traces (as traces of different items become stronger their similarity decreases). This mechanism also is a key to understanding the development of knowledge (Nelson & Shiffrin, 2013).
Consider another example involving the role of testing. Following Izawa (1970), Murdock and Anderson (1975), and later Roediger and Karpicke (2006), Criss, Malmberg, and Shiffrin (2011) noted that interference caused by testing items other than those studied builds up over the course of recognition testing. In fact, this interference is larger than simply adding more different items to a study list. These recognition findings seem to be paradoxical: Increasing the strength of some items helps recognition of other items, and increasing the number of studied items only slightly harms recognition memory, but increasing the number of items tested produces a stronger negative effect upon recognition. Helping to understand the basis for such effects is the finding that the interference arising from testing occurs within a test block of similar items, but then recovers when the next block of tests are for items dissimilar to the prior block (Malmberg, Criss, Gangwani, & Shiffrin, 2012).
Kilic, Criss, Malmberg, and Shiffrin (2017) used extant encoding assumptions to describe these consequences of testing in recognition studies. The key assumption involved updating of a prior trace of an item when that item is tested: A prior trace that sufficiently well matches the test stimulus is updated with additional item information, an updating that occurs regardless of whether the test stimulus had previously been studied or not. Malmberg, Lehman, Annis, Criss, and Shiffrin (2014) reprised the Atkinson and Shiffrin approach to the findings concerning testing, and the complex issues that such findings raise, in a chapter in The Psychology of Learning and Motivation.
These two examples show how an increase in understanding was facilitated by use of the framework of the modal model and its subsequent development. The modal model, in both its original broad outline and in its developed form today, remain a standard for research and theory development in the field. Although this modal model, as with all models of human memory, remains a work in progress. It seems likely to remain a standard reference for future developments for many years to come.
References
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Atkinson, R.C. & Juola, J.F. (1974). Search and decision processes in recognition memory. In D.H. Krantz, R.C. Atkinson, R.D. Luce, & P. Suppes (Eds.), Contemporary developments in mathematical psychology. Vol. 1. Learning, memory and thinking. San Francisco: Freeman.
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Malmberg, K.J., Lehman, M., Annis, J., Criss, A.H., & Shiffrin, R.M. (2014). Consequences of Testing Memory. In Brian H. Ross editor: The Psychology of Learning and Motivation, Vol. 61, Burlington: Academic Press, 2014, pp. 285-313.
Malmberg, K.J., Raaijmakers, J.G.W., & Shiffrin, R.M. (2019). 50 Years of Research Sparked by Atkinson and Shiffrin (1968), Memory & Cognition.
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