SHORT 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
LONG TERM MEMORY
– The permanent memory store
– Memory for events that has happened in the past
– Unlimited capacity
– Unlimited duration
– Coding is semantic
CAPACITY
– 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
STM – DIGIT SPAN
– 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
STM – THE MAGIC NUMBER
– 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
EVALUATION OF CAPACITY
TEMPORAL VALIDITY
– 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.
CAPACITY MIGHT BE MORE LIMITED
– 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.
INDIVIDUAL DIFFERENCES
– 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.
DURATION
– The length of time information can be held in memory
– LTM potentially lasts forever
– STM has a short duration
THE DURATION OF STM
– 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.
THE DURATION OF LTM
– 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.
EVALUATION OF DURATION
ARTIFICIAL
– 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.
HIGH EXTERNAL VALIDITY
– 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.
CODING
– 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
ACOUSTIC AND SEMANTIC CODING
– 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
EVALUATION OF CODING
ARTIFICIAL
– 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.
STM MAY NOT BE EXCLUSIVELY ACOUSTIC
– 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.