Experiments have shown that the sensory register holds information for up to 50 milliseconds (Sperling, 1960). His experiment used arrays of letters (12 letters in total) and a subject was exposed to these letters for 50 milliseconds, and then asked to recall as many as possible. The subjects could only recall 4 or 5 of the letters and when presented with the letters for less than 50 milliseconds only on occasion were any letters recalled at all. This then proved that the sensory memory register needs 50milliseconds at least for information to be taken in and used, this process is also called iconic storage.
The information that has been chosen from the sensory register for further storage (the information which has been paid attention to) is then transferred to the short term memory (STM) where it is held for up to 30 seconds longer, and can be manipulated further. It has been suggested that the short-term memory can usually hold from 5-9 items (Miller, 1956). A number could be looked at for no more than 0.5 seconds (the time it takes for sensory register to take in the information), then the participant can count down from 10 to zero, this reduces the chance of rehearsal and hence transferring the information to the long term memory. This method can then be repeated using a larger amount of numbers each time, in most cases the participant should find that they could only remember the number is it is from 5-9 digits long. If the information in the short-term memory is need for a more long-term use then it can be sent to the long-term memory either by voluntary or in-voluntary rehearsal. As an example a telephone number that needs to be remembered is usually repeated in the person’s head until they are happy they can remember it. Whereas some information may be sent to long-term memory without rehearsal for instance a television advertisement may be remembered and recited even those you have not voluntarily placed that information into your long-term memory. The information stored in the short term memory is thought to be stored as sound (acoustic encoding), for example when remembering a telephone number it is stored as it is spoken in the short term memory, whereas when information is stored in the long term memory it is stored as it is written and in terms of meaning (semantic encoding).
The long-term memory is the vast database of information in the brain, the information has at some point been transferred through the sensory register and short-term memory to the long-term memory where it is stored indefinitely. As mentioned earlier the information transported to the long-term memory is usually voluntary, there are processes involved in placing the information in the long-term memory, these are called the control processes. First the relevant information is selected and manipulated giving special attention to certain items. If there is any related information in the long-term memory then the new information is linked so that upon the need for retrieval items from different situation and times can be recalled for one subject. The size of the long term memory and how long information stays there for has yet to be discovered, and many scientists believe that although many people cannot remember much from childhood, that the memories are still there yet it cannot be reached.
In 1974 Baddeley and Hitch weren’t convinced that the modal model proposed by Atkinson and Shiffrin six years earlier, and produced a more complex version of the structure of memory. Baddeley and Hitch agreed with the long term memory ideas that Atkinson and Shiffrin put forward but disagreed about the short-term memory. The model Baddeley and Hitch worked on was called the ‘Working Memory Model’ Baddeley and Hitch (1974), and was composed of a more complex short-term memory system than previous models. The short-term memory suggested was made up of 3 sections; the central executive, articulatory loop and the visuo-spatial scratch pad, all working together to transmit information to and from the long-term memory.
The central executive is the least known section of the short-term memory in this model and it is still to be explored as o what exactly happens in the central executive, however the important facts are known. The main task of the central executive is to pass the information to and from it’s two slave systems; the articulatory loop and the scratchpad, and is also involved in the decision making of receiving information. It was also proposed by Baddeley and Hitch that their short-term memory model was not modally selective and could deal with the stimuli from different (or the same) senses at the same time. This theory was tested (Robbins et al 1996) using a chess game set up. Two participants played a game of chess with each other (participants varying in skill levels) whilst undertaking other activities at the same time for instance; repetitive tapping, repeating words and pressing keys on a keypad in a clockwise motion. This illustrated that many sources of information could be handled at the same time using the central executive model. The better moves of the more experienced players also reflected the idea that they use the long-term memory more to retrieve tactical information and therefore turned out to be better also at the supplementary tasks.
The articulatory loop of the system receives the audio information and stores this information as acoustic coding. When a telephone number is received for example it needs to be rehearsed so that it can be transferred to the long term memory, normally the number would leave the phonological store of the short term memory within 2 seconds of receiving the information this is where the articulatory control process comes in help. The process is that of repetition, the information in the phonological store needs to be repeated either out loud or silently to yourself so that it can travel around the loop and back into the phonological store again before it is lost. Once the information has been repeated enough it will then become apparent in the long-term memory, where it can be recalled when needed.
The second slave to the central executive is the visuo-spatial sketchpad that is responsible for receiving and manipulating the visual and spatial information from the senses. There are two main processes in the sketchpad; the visualizing of images and spatial awareness within the mind, the ‘inner eye’ ( Baddeley, Thompson and Buchanan, 1975) and also controlling the images received from the physical eye and making us aware of the surroundings around us. This slave system is linked to the articulatory loop and both work together, as illustrated in the matrix experiment (Baddeley et al, 1975). This involved a 4 x 4 matrix of squares and a subject was given instructions to place numbers in the boxes, upon completion the subject is then asked to repeat the sentences of instructions as they were read out to them. This involves the use of both the slaves in the system as the sentences are constructed from the visual image of the matrix stored.
Having looked at the two models of the structure of the memory, the difference between them is the complexity of the short-term memory. Both models however could be interpreted as being correct and both provide solid reasoning behind the working of the memory. If a simple approach to the aspect of memory was needed then the Atkinson and Shiffrin’s modal model would be a beneficial explanation however more understanding and research into the memory may require a more complex approach, this is where Baddeley and Hitch working memory model would be useful.
References
Baddeley, A.D., Grant S., Wight, E. and Thompson, N. (1975) ‘Imagery and visual working memory’, in P.M.A. Rabbit and S. Dornic (eds) attention and performance, V, pp. 205-217, London: Academic Press
Sperling, G. (1960) Psychological Monographs: General and Applied, 74, 1-29
Miller, G. (1956) Psychological Review, 63, 81-97
Atkinson, R.C. & Shiffrin, R.M (1968) ‘The Psychology of Learning and Motivation: Advances in Research and Theory’ (vol. 2) New York: Academic Press
Baddeley, A.D. & Hitch, G. (1974) ‘The Psychology of Learning and Motivation’ (vol. 8) New York: Academic Press.
