A Brief History of Human Memory Systems Research

Early models and measures of memory

Some of the first notable noted research on human memory was conducted in 1890 by William James. Based on his research, James assumed memory consists out of two systems (dichotomous memory)1) Loftus, G. R., and Elizabeth F. Loftus. Human Memory: The Processing of Information. Routledge, 1976. :

primary memory, which lasts for a few seconds and holds information in our consciousness, and

second memory, which has unlimited duration and can be brought to consciousness if desired.

A measure for the capacity of short-term (primary) memory was first introduced even a bit earlier, in 1887, by Joseph Jacobs, who tested the span of digits his students were able to remember.2) Jacobs, J. Experiments in 'prehension'. Mind, 12, 75-79, 1887. Cited by Baddeley, Alan D. Human memory: theory and practice. Psychology Press, 1997. Under the criterion that at least 50% of the digits need to be remembered correctly, subjects he tested mostly remembered about 7 digits. What he also noticed is that this result can be improved by grouping the digits (for example in groups of three), or reading aloud.

Similar results were reported by George Miller in 19563) Miller, G. A. The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63, 81–97. 1956. . Based on his research, he suggested human short-term capacity was determined by the number of chunks or cognitive wholes one can remember, no matter if it is a letter, digit or word. This number on average equals seven, and may vary usually between five and nine.

This research increased interest in human memory research. Until then, it was commonly accepted that forgetting occurs due to interference of target information with new acquired information. This idea known as retroactive interference4) Forgetting of learned information due to newly acquired information. was introduced in 1900 by Georg Elias Müller and Alfons Pilzecker5) Müller G.E., & Pilzecker A. Experimentelle Beiträge zur Lehre vom Gedächtnis. Z. Psychol. Ergänzungsband 1:1–300. 1900. cited by Lechner, Hilde A., Larry R. Squire, and John H. Byrne. 100 Years of Consolidation — Remembering Müller and Pilzecker. Learning & Memory 6, no. 2: 77-87, March 1999. who concluded that learning does not cause instantaneous and long lasting memories, but that memory takes time to consolidate (Konsolidierung). This also means that during the consolidation period the memory is vulnerable.

During the 1950s John Brown6) Brown, J. Some Tests of the Decay Theory of Immediate Memory. Quarterly Journal of Experimental Psychology 10, 12-21. 1958. and Lloyd and Margaret Peterson7) Peterson, L. R., & Peterson, M. J. Short-term retention of individual verbal items. Journal of Experimental Psychology, 58, 193-198. 1959. conducted research on information forgetting, offering other explanations of forgetting. Their hypothesis was that forgetting occurs due to the rapid decay of the memory trace (the neural substrate of retention) when it is first established. Both reasons will later be accepted as correct.

One or two memory systems?

Another issue discussed during 1960s was weather human memory system has one or two components. Some authors like Arthur Melton8) Melton, Arthur W. Implication of short-term memory for a general theory of memory, October 1963. argued that both short term memory (STM) and long term memory (LTM) are just two subcomponents dependent on the same system. He justified his views by proofs of activation of the LTM in STM experiments. His work was very influential, yet during the years more and more evidence of at least two separate memory systems have accumulated.

The multi-store model of Atkinson and Shiffrin. Image borrowed from: Wikipedia: Memory. Click on the picture to follow the link. The first more influential two component memory model was introduced in 1968 by Richard Atkinson and Richard Shiffrin9) Atkinson, R.C. & Shiffrin, R.M. Chapter: Human memory: A proposed system and its control processes. In Spence, K.W.; Spence, J.T. The psychology of learning and motivation (Volume 2). New York: Academic Press. pp. 89–195. 1968. . Their model called Multi-store model consisted of long-term and working or short-term memory model and was later improved by an additional component, the sensory memory. Sensory memory contains one register for each sense and serves as an short lasting buffer-zone before the information can enter short-term memory. Short-term memory is a temporal storage for new information before it enters long-term memory, but is also used for cognitive tasks, understanding and learning.

The thesis of two separate memory systems: the long-term memory and the short-term memory is today considered to be true. This thesis is supported by differences in10) Cowan, N. What are the differences between long-term, short-term, and working memory? Progress in brain research 169: 323-338. 2008. 11) Mcleod, Saul. Memory Psychology. Simply Psychology, 2007. :

capacity (small for STM and large or unlimited for LTM),

duration limits (items in STM decay as a function of time, which is not a characteristic of LTM),

retention speed (very high for STM and possibly lower for LTM),

time to acquire information (short for STM and longer for LTM),

information encoding (semantic for LTM and acoustic or visual for STM), and

type of memory affected by physical injuries in patients12) See: Milner, B. Amnesia following operation on the temporal lobes. In C.W.M. Whitty & O. L. Zangwill (eds), Amnesia. London: Butterworth, 1966. (damage of LTM without damaging STM), and Shallice, T. & Warrington, E.K. Independent functioning of verbal memory stores: a neuropsychological study. Quarterly Journal of Experimental Psychology, 22, 261–273. 1970. (damaged STM with fully functioning LTM), cited by Baddeley, Alan D. The Psychology of Memory. In Michael D. Kopelman, and Barbara A. Wilson. The Handbook of Memory Disorders. 2nd ed. Wiley, 2002. .

Another term should be clarified here: the working memory, which is often mistaken for the short-term memory. The main difference between these two is that working memory usually includes the structure and processes performed by a system in control of the short-term memory.

Bibliography

Rončević Zubković, Barabara. Ustrojstvo radnog pamćenja i njegova uloga u jezičnom procesiranju. Psihologijske teme 19, no. 1: 1-29. 2010.

Lechner, Hilde A., Larry R. Squire, and John H. Byrne. 100 Years of Consolidation — Remembering Müller and Pilzecker. Learning & Memory 6, no. 2: 77 -87. March 1, 1999.