Short Term Memory

• Miller (1956) used the serial recall technique to test capacity
• Miller (1956) called his experiment the digit span experiment. This technique asks participants to serially recall lists of numbers back to the researcher immediately after seeing them. Each trial adds another number
• Miller found that participants on average could remember between five and nine digits of information before starting to make mistakes
• Miller also found that it seemed easier to remember digits rather than letters because there are only nine digits but 26 letters
• Miller also found that if participants were able to chunk information together meaningfully then the amount of information remembered would increase
• Baddeley (1966) used word lists to test for acoustic and semantic encoding in STM
• Baddeley presented word list for ps to remember and recall. One set of words contained acoustically dissimilar and the other set of words contained acoustically similar words
• Baddeley found that acoustically similar words were harder to recall than dissimilar words. This may be because STM is largely encoded acoustically and so so acoustically similar words are more likely to be confused
• Peterson and Peterson (1959) used the trigram technique to test for STM duration
• Peterson and Peterson briefly showed ps a consonant trigram. Ps were asked to count backwards in threes from a specified number to stop them thinking about the letters. after the intervals of 3, 6, 9, 12, 15 or 18 seconds, ps were asked to recall the original trigram. The procedure was repeated several times using different trigrams
• Peterson and Peterson found that ps were able to recall 80% of trigrams after a 3 second interval. Progressively fewer trigrams were recalled as the time intervals lengthened. After 18 seconds, fewer than 10% of the trigrams were recalled correctly
• Peterson and Peterson concluded that if rehearsal is prevented, information vanishes rapidly from STM. Therefore, decay is the mechanism for forgetting in STM
• Cowan (2001) reviewed a variety of studies on the capacity of STM and concluded that STM is likely to be limited to about four chunks. Research on the capacity of STM for visual information also found that four items was about the limit. This means that the lower end of miller‘s range is more appropriate which suggests that STM may not be as extensive as was thought
• Simon (1974) found that people had a shorter memory span for larger chunks, like eight word phrases, than smaller chunks like one-syllable words which supports the view that STM has a limited capacity and refines our understanding
• In the petersons’ study ps were counting the numbers in their STM and this may displace or ‘overwrite’ the syllables to be remembered. Reitman (1974) used auditory tones instead of numbers so displacement wouldn’t occur and found that the duration of the STM was longer
• Brandimote et al (1992) found that ps used visual coding in STM if they were given a visual task and prevented from doing any verbal rehearsals in the retention interval before performing a visual recall task. Normally we ‘translate’ visual images into verbal codes in STM but, as verbal rehearsal was prevented, ps used visual codes which suggests that STM isn’t exclusively acoustic