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⁾ :

• primary memory, which lasts for a few seconds and holds information in our consciousness, and
• secondary 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⁾ 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⁾ . 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 interference ⁴⁾ was introduced in 1900 by Georg Elias Müller and Alfons Pilzecker ⁵⁾ 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 Brown ⁶⁾ and Lloyd and Margaret Peterson ⁷⁾ 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.

Another issue discussed during 1960s was weather human memory system has one or two components. Some authors like Arthur Melton ⁸⁾ 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 first more influential two component memory model was introduced in 1968 by Richard Atkinson and Richard Shiffrni ⁹⁾ . 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 in^{10) 11)} :

• 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⁾ .

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.

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.