The evidence for short term memory and its hypothetical construct and its nature

The recency effect suggests that the capacity of short-term memory is about two or three chunks whereas the span measures indicate a capacity of about seven chunks.  One reason for this difference is the different pattern of rehearsals that take place for each assessment.  Both the recency effect and span measures providence evidence showing that the capacity of short-term memory is limited.

An experiment by Peterson and Peterson in 1959  known as the “Brown – Peterson technique” was used to demonstrate the duration of a short term memory.  Participants were required to remember a fairly artificial kind of data: trigrams ( three consonants) and then later recall them after different, set, time periods.  They were also given an interference task to prevent them rehearsing the trigram.  The simple nature of this experiment meant that we could clearly identify the effect of the independent variable (time delay) on the dependant variable (recall). The conclusion was that short-term memory would just about disappear after 18 seconds.

Short term memory can also be defined by the concept of encoding, a concept likely to be less familiar than the capacity and duration of short-term memory.  Encoding refers to the way in which information is stored in the memory.  It was found by the psychologist Baddely using free recall, that short-term memory largely uses an acoustic code where the words are stored in relation to the way they sound.  This was found due to participants not confusing words that had the same meaning, but often-confusing words that sounded similar.  Conrad (1964) also investigated into encoding and presented data that also showed that participants made errors during the encoding of words that sounded the same.  Later research by Posner in 1969 demonstrated that visual codes do in fact exist in short-term memory, at least some of the time.  This was shown by an experiment wherebye participants wer shown letters of the same sound but were sometimes mixed into different forms i.e. aA and AA. Participants had to say whether the letters were the same or different in this free recall natured experiment.

Further Evidence about short-term memory came from studies of brain damage by Warrington and Shallice in 1970.  They studied a participant who had suffered brain damage.  The participant had no problem with long-term memory, but had an extremely poor digit span indicating his short-term memory was drastically reduced.  Combined with the knowledge of amnesia – when a person loses much of their long-term memory due to brain damage but had almost normal short-term memories, it was suggested that different parts of the brain are involved in short-term and long-term memory.  Further studies from Warrington and Shallice gave additional insight into short term memory.  It was found that the participant earlier assessed would forget things that were heard much more than the forgetting of visual stimuli.  They also found that the participants short-term memory deficit was limited to verbal materials and did not extend to meaningful sounds.  This further suggested that there is a number of different stores of more than one short term memory, each represented in different parts of the brain.