Short Term and Long Term Memory


 – The limited capacity memory store

– Your memory for immediate events

– Memories disappear unless they are rehearsed

– Capacity is between 5-9 items

– Duration is between 18-30 seconds

– Coding is mainly acoustic

– Sometimes referred to as working memory


– The permanent memory store

– Memory for events that has happened in the past

– Unlimited capacity

– Unlimited duration

– Coding is semantic


– How much data can be held in a memory store

– STM has a limited capacity to 7 土 2 characters

– LTM has an unlimited capacity


– Jacobs (1887) used this technique to assess STM capacity

– The researcher gives, for example, 4 digits and then the participant is asked to recall these in the correct order out loud

– If this is correct the researcher reads out 5 digits and so on until the participant cannot recall the correct order anymore

– This determines the individual’s digit span

– He found that the average span was 9.3 items and 7.3 for letters


– Miller (1956) noted that things tend to come in sevens: there are 7 days of the week, 7 deadly sins ect.

– He reviewed psychological research and conducted the span if immediate memory is about 7 items, sometime more and sometimes less

– Miller also noted that people can recall 5 words as well as they can recall 5 letters.

– They do this by chunking, by grouping sets of digits or letters into units or chunks



– One criticism of Jacobson’s study is that it was conducted a long time ago

– Early research in psychology often lacked adequate control.

– For example, some participants may have been distracted while they were been tested so they didn’t perform as well as they might.

– This would mean that the results would might not be valid because the confounding variables that were not controlled.

– However, the results of this study have been confirmed other research supporting its validity.


– One criticism of the research investigating STM is that Miller’s original findings have not been replicated.

– Cohen reviewed a variety of strut studies on the capacity of stm and concluded that STM is likely to be limited to about 4 chunks.

– Research on the capacity of STM for visual information (rather than verbal stimuli) also found that four items was about the limit.

– This means that the lower end of Miller’s range is more appropriate (5)

– This suggests that stm might not be as extensive as was thought.


– Jacobs also found that that digit span increased with age

– 8 year olds could remember an average of 6.6 digits

– Whilst for 19 year olds the average was 8.6 digits

– This age increase might be due to gradual increase in brain capacity or development of strategies to increase digit span.


– The length of time information can be held in memory

– LTM potentially lasts forever

– STM has a short duration


– Peterson and Peterson (19590 studied the duration of STM, using 24 students.

– Each participant was tested over 8 trials.

– On each trial a participant was given a consonant syllable and a 3 digit number (eg. THX 512)

– They were asked to recall the consonant syllable after a tension interval of 3, 6, 9, 12, 15 or 18 seconds.

– During the retention interval they had to count backwards from the three digit number.

– Participants, on average were 90% correct over 3 seconds, 20% correct after 9 seconds and only 2% correct after 18 seconds.

– This suggests that STM has a very short duration (less than 18 seconds) as long as verbal rehearsal is prepared.


Bahrick et al (1975) studied 392 participants from Ohio, USA who were aged between 17 and 74.

– High School yearbooks were obtained from the participants or directly from some schools.

– Recall was tested in various ways, including:

– Photo recognition test consisting of 50 photos, some from the participants high school yearbook

– Free recall test where participants record all the names of their graduating class.

– Participants who tested within 15 years of graduation were about 90% accurate in the photo recognition.

– After 48 years, recall declined to about 70% for photo recognition.

– Free recall was less good than recognition.

– After 15 years this is about 60% accurate, dropping to about 30% after 48 years.

– This shows that LTM can last a very long time indeed.



– A criticism of Peterson and Peterson study is that their study was artificial.

– Trying to memorise consonant symbols does not really reflect most everyday memory activity is where what we are trying to remember is meaningful.

– Therefore, the study lacks external validity and mundane realism

– However, we do sometimes try to remember 30 meaningless things, such as groups of numbers (phone numbers) or letters (postcodes).

– This means that, although the task was artificial, the study does have some relevance to everyday life.


– One strength of Bahrick et al’s study is that it has higher external validity than Peterson and Peterson.

– Real life meaningful memories were studied.

– When studies on LTM have been conducted with meaningless pictures to be remembered, recall rates were lower.

– The downside of such real-life research is that confounding variables are not controlled, as Bahrick’s participants may have looked at their yearbook photos and rehearsed their memory over the years, leading to individual differences

– Therefore although there is high external validity it is hard to control the confounding variables.


– The format in which information is stored in memory

– Information enters the brain via the senses and is then stored in various forms

– Visual (images)

– Acoustic (Sounds)

– Semantic (meaning)

– STM tends to be coded acoustically

– LTM tends to be coded semantically


– Baddeley (1966) gave a different list of words to 4 groups of participants to remember.

Group 1 – Acoustically similar – words sounded similar e.g. cat, cab, can.

Group 2 – acoustically dissimilar – words that sound different e.g. pit, view, cow.

Group 3 – semantically similar – words with similar meanings e.g. great, large, big.

– Group 4 – semantically dissimilar – words that had different meanings e.g. good, huge, hot.

– Participants were shown the original words and asked to recall them in the correct order.

– When they had to do this recall task immediately after hearing it they tended to do worse with acoustically similar words.

– If participants were asked to recall the word list after a time interval of 20 minutes, they did worse with the semantically similar words.

– This suggests that information is coded semantically in LTM and acoustically with ST



– One limitation of Baddeley’s study was that it used quite artificial stimuli rather than meaning for material.

– The word list had no personal meaning to participants.

– This means that we should be cautious about generalizing the findings to different kinds of memory task.

– For example, when processing more meaningful information, people may use semantic coding even for the STM tasks.

– This suggests that the findings from this study have limited application andthe study lacks external validity and mundane realism.


– Some experiments have shown that visual codes are also used in STM.

– One study found that participants use visual coding in STM if they were given a visual task (pictures) and prevented from doing any verbal rehearsal in the retention interval (they had to say ‘la la la’) before performing a visual recall task.

– Normally we translate visual images into visual codes in STM but as verbal rehearsal was prevented, participants used visual codes.

– Other research has shown that STM sometimes uses a semantic code.

– This suggests that STM is not exclusively acoustic.