Please enable JavaScript.
Coggle requires JavaScript to display documents.
Features of STM and LTM (Key Terms (Capacity: A measure of how much can be…
Features of STM and LTM
Capacity
STM
Jacobs (1887) used the digit span technique to measure the capacity of STM. He found the average span for digits was 9.3 items and 7.3 for letters. Jacobs proposed more digits could be recalled as there are only 9 digits compared to 26 letters.
The magic number 7+- 2 After reviewing research, Miller (1956) concluded that the span of STM is 7 plus or minus 2 items. When dots are flashed on a screen people are able to count 7 dots but not many more. This is the saem for musical notes, letters and words. Miller further proposed STM capacity can be enhanced by grouping sets of digits and letters into meaningful unitsknown as 'chunks'.
Evaluation
The capacity of STM may be even more limited Cowan's (2001) review of STM capacity studies suggests that capacity is more likely to be limited to about 4 chunks of information rather than 7+-2 items. This is supported by research into the capacity for visual stimuli which found that 4 items was the limit (Vogel et al., 2001)
The size of the chunk matters The size of the chunk seems to affect how many chunks can be recalled. Simon (1974) found that people had a shorter memory span for eight word phases (larger chunks) than for one-syllable words (smaller chunks)
Individual differences Individual differences mean the capacity of STM varies between people. Jacobs found digit span (the ability to recall items in a list) increases with age; eight year olds could recall an average of 6.6 digits whereas for 19 year olds the mean recall was 8.6 digits
-
Duration
STM
How? Peterson (1959) devised a laboratory experiment to test 24 students over 8 trials. Each trial consisted of the participant being given a consonant syllable and a three-digit number. Participants recalled the consonant syllable after a retention interval during which they counted backwards from the three-digit number presented. Recall was tested over retention intervals of 3, 6, 9,12, 15 and 18 seconds.
Showed? On average, particiapnt recall of the consonant syllable was 90% correct over 3 seconds, 20% correct after 9 seconds and only 2% correct after 18 seconds. This suggests that when verbal rehearsal of the consonant syllable is prevented the duration of STm is very short.
LTM
How? In a natural experiment, Bahrick et al. (1975) tested over 400 people, aged 17-74 years, for their memory of classmates from when they were at school. A photo-recognition test required participants to identify high-school yearbook images of thier classmates from 50 photos. In a free-recall test participants listed names of classmates in their graduating class.
Showed? In the photo-recognition task, participants tested within 15 years of graduating from high school showed 90% accuracy when identifying photos of their classmates. After 48 years this declined to about 70% accuracy. For free-recall of classmates' names participants were 60% accurate after 15 years whereas after 48 years recall accuracy fell to 30%.
Evaluation
Peterson and Peterson's testing was artificial People don't normally want or need to remember meaningless consonants so the test did not reflect everyday memory activities. However, it could be said we do sometimes try to remember fairly meaningless items such as groups of numbers (phone numbers) or letters (post codes). Therefore, the study could hold some relevance to memory in everyday life.
STM results may be due to displacement not decay The counting task may have displaced the memory of the syllable. Reitman (1974) used auditory tones instead of counting which prevents displacement and found the duration of STm was longer. If the forgetting seen in the Petersons' study was due to displacement rather than decay the duration of STM was not measured.
LTMs may have been regularly rehearsed In Bahrick et al's. study participants may have kept in contact with their classmates and seen them over the years since graduation. This would explain the high levels of recall seen as they would be rehearsing the memory of their classmates every time they met, spoke to or though about them.
Coding
Coding in STM and LTM
How? In a laboratory experiment Baddeley (1966) gave particpants lists of words that were acoustically similar or dissimilar and lists of words that were semantically similar or dissimilar.
Showed? When testing STM, participants had difficulty remembering acoustically similar word lists but could recall semantically similar words. In LTM, participants became muddled when recalling semantically similar words but were able to recall acoustically similar word lists. This suggests that STM uses acoustic coding whereas LTM uses semantic coding.
Evaluation
Baddeley may not have tested LTM When testing STM, Baddeley asked participants to recall a word list immediately after hearing it. LTM was tested by recalling 20 minutes after hearing the word list. It is questionable as to whether this is a sufficient amount of time to test LTM.
STM may not be exclusively acoustic Brandimonte et al. (1992) found that when participants were given a visual task and prevented from using verbal rehearsal they were still able to perform well ona visual recall task. Normally, we would translate the visual images into a verbal code in STM but saying la,la,la repeatedly prevented this, meaning participants used visual codes.
LTM may not be exclusively semantic Frost (1972) showed that recall in LTM was related to visual as well as semantic categories. Nelson and Rothbart (1972) found evidence of acoustic coding in LTM. Therefore, LTM does not seem restricted to semantic coding. As with STM the coding used varies according to circumstances.
Key Terms
Capacity: A measure of how much can be held in memory. Measured in bits of information, such as the number of digits. STM has a limited capacity. LTM has a potentially infinate capacity.
Coding: The way information is changed so that memory can be stored. Information entering the brain via the senses is stored as visual codes (images), acoustic codes (sounds) or semantic codes (the meaning of experiences).
Duration: a measure of how long a memory lasts before it is no longer available. LTM potentially lasts forever but STM has a short duration, meaning information is quickly lost unless it is repeated over and over again is a process called maintenance rehearsal.
Long-term memory (LTM): Memory for events that have happened in the past. This lasts anywhere from 2 minutes to 100 years. LTM has potentially unlimited durationand capacity and tends to be coded semantically.
Short-term memory: Memory for immediate events. Measured in seconds and minutes rather than hoursor days. Short-term memories, as last for a very short time and disappear unless rehearsed. STM also has a limited capacity and tends to be coded acoustically. This type of memory is sometimes referred to as working memory.
