What is the duration and capacity of sensory, short-term, and working memories?
The Modal Model of the Mind was proposed by a number of psychologists (Atkinson & Shiffrin, 1968; Waugh & Norman, 1965) in order to explain how our brain stores information. The model proposes three different "storage units" where information is sent, processed, and kept. Each of these "storage units" are different in terms of their capacity and their function throughout the process. The process of memory storage is dependent on what are known as "control" processes (opposite of variable) that include a) the senses, b) how the information is put in (input), c) level of attention, d) MRE (maintenance rehearsal encoding), and e) the final retrieval.
The first type of memory is the echoic, or sensory memory. This is basically what you first hear during input. According to Atkinson & Shiffrin (1968) the duration of this type of memory, which is the shortest, is about 4-10 seconds. If the input is given in a manner which attracts and sustain the attention of the listener, the input will then move to the SHORT term memory.
The short term memory is the second, short-term storage unit in the brain. According to what is known as "Miller's Magic Number" (Miller, 1956), the capacity for short-term memory comes with a formula which Miller calls the "magical number 7 plus 2", or 7+2 . Miller states that short term memory does vary among different people. However, his proposal states that information, or input, should be given in chunks. In his research, the majority of his participants were able to recall 7 chunks of input plus two more. Short term memory lasts from 20 to 30 seconds, according to research. This lapse of time is dependent on interference from other events, noises, or interruptions taking place, or for memory loss that is caused by biological or cognitive issues.
Long term memory (LTM) is the final and most capable of all the storage units in the brain. It is also the one upon we depend the most. The most recent research has been conducted chiefly by Eric Kandle, Nobel Prize winner (2000) and it is based on the development of drugs that mimic the LTM process of keeping in maintaining information. As with every other research done before, the final conclusion is that LTM has both unlimited capacity and unlimited duration. Depending on environmental and physical factors, LTM will vary from person to person. However, the same researchers have also concluded that LTM is the last of the three types of memory storage units to become affected by variable factors. This is because of its resilience, and because the input was processed effectively in order to be stored in the LTM.
These findings present a strong implication for educators all over the world to understand how it is that students retain information and through which methods this is done most effectively.