Conclusions –findings suggest nature of encoding is different in STM and LTM.
- STM- is acoustic not semantic
- Encoding is on the basis of sound not meaning
- We rehearse/say over words in STM.
- LTM- coding is semantic, not acoustic
-Encoding based on meaning of word not sound.
Criticisms
- Study lacks mundane realism – people in real life do not learn word lists under controlled conditions- experiment lacks ecological validity, not generalise to everyday memory.
- Not all information in LTM is in semantic form –words are presented visually in STM task.
-only know how to pronounce them because information about word sounds, stored in LTM.
- More codes than acoustic and semantic- other codes preferred depending on nature of information encoded.
-Posner (1969)- Visual coding preferred over acoustic in STM.
-AA processed rapidly than Aa – 2 letter combinations do not differ acoustically.
Information in LTM encoded acoustically, visually, taste, smell.
Capacity in Short-term Memory
Aims: Investigate how much information can be held in STM.
-Jacobs needed an accurate measure of STM capacity – devised technique “serial digit span”.
Procedure: Laboratory experiment using digit-span
- Participant presented with letter/digit sequences – serial recall (repeat back letters/digits in same order presented)
- Pace of item presentation controlled- ½ second intervals through metronome.
- Sequence- 3 items, increased by 1 item until participant failed to reproduce sequence correctly.
- Number of trails repeated – establish participants digit/letter span
- Longest sequence lenght-50% trails taken to be participants STM span/digit/letter span.
Findings – Average STM span (number of items recalled between 5-9 digits.
-Digits recalled better (9.3 items) and letters 7/3 items.
-Individual differences –STM span increased with age- 6.6 average for 8 year olds and 8.6 for 19 year olds.
Conclusions- Findings show STM has limited storage capacity –between 5-9 items.
-STM- capacity not determined by nature of information learnt –size of STM span – constant across individuals.
-Individual differences as STM span increased with age – increasing brain capacity/improved memory techniques- chunking.
Criticisms
- Historical importance- represents first systematic attempt to assess capacity of STM
Key Findings-capacity is small.
- Research lacks mundane realism-digit-span task not representative of everyday memory demands
-Artificiality of task-biased result
-Letters/digits not meaningful- remembered less well than meaningful information.
-Capacity of STM- greater for everyday memory
-Jacobs’s findings-not safely generated to real life memory. Ecological validity?
Argument- meaningful material produces less “pure” measure of STM capacity – participants make use of LTM to improve performance.
- Findings – usefully applied to improve memory.
-Telephone numbers, codes, car registration- based on total digit span idea,
-Memory –improvement techniques based on findings-digit span cannot be increased – size of information can be.
Chunking- applied in mnemonics (memory aids) – ROY G BIV= colours of rainbow.
Duration of Short-term memory
Study: Peterson and Peterson’s 1959, study of duration of short-term memory
Aims: 1950’s- How long information remains in STM
-Peterson and Pterson- study issue using simple stimuli
-Not allowing participants to rehearse material presented
-Information could remain in STM for long periods of time if participants rehearsed it.
Procedure:- Peterson and Peterson used Brown- Peterson technique
- Each trial-participants presented with trigram- 3 constantans (BVM, CTG)
-would be asked to recall in correct order.
-recall required after delay of 3,6,9,12,15,18 (18 seconds)
-Participants count backwards in threes from random digit number (866, 863, 860) – between presentation of trigram and time asked to recall it.
-Recall had to be 100% accurate and in correct order (serial recall) in order to count.
-Participants tested repeatedly variable –time delay
-Dependent variable- number of trigrams recalled.
Findings: Increase in forgetting from STM as time delay increased.
-After 3 seconds –80% trigram recalled
-After 6 econds-50% recalled
-After 18 seconds- less than 10% recalled
-Little information remained in STM for more than 18 seconds.
Conclusions: Findings suggest information held in STM is lost rapidly when there is no opportunity to rehearse it.
- Information in STM is fragile and easily forgotton
-STM is distinct from LTM- forgetting is faster from STM than from LTM.
Criticisms
- Peterson and Peterson used artificial stimuli (trigram)-lack in meaning
-Study lacks mundane realism and ecological validity-STM is likely to be better for meaningful stimuli in everyday life than for stimuli used in study.
- Peterson and Peterson findings- depended in part on the fact that participants given many trials with different trigrams- became confused.
-1962- Keppel and Underwood- used same task- observed no forgetting over time on first trial.
-Forgetting caused in part by proactive interference-disruption of central learning and memory by previous learning.
-First trigram-free from proactive interference.
Encoding in Long-term memory
Duration in Long term Memory
Study: 1975- Bahrick et al’s
Aim: Bahrick et al –to investigate duration of very long-term memory (VLTM)
-Show memories last over several decades –support assumption that duration of memory-lifetime
-Aimed to test VLTM in ecologically valid way- testing memory for real life information.
Procedure-sample of 392 ex-high school students- 17-71
- Free recall of names of former class mates
- Photo recognition test-identity class mates in set of 50 photos-only were thier classmates
- Name recognition test
- Name and photo matching test
-Tests assesses VTLM- time since leaving high school was 48 years.
-Participant’s accuracy (duration of memory)- assessed comparing responses with yearbooks with pictures and names of all students.
Findings: Bahrick et al found- 90% accuracy in face and name recognition- even for those whi left 34 years previously
- 80% name recognition, 40% face recognition- 48 years.
Free recall less accurate- 60%-15 years
- 30%- 48 years.
Conclusion: - Before research by Bahrick et al- assumption that information could remain in LTM for long periods of time- No experimental tests of this assumption
- Classmates faces and names- particular type of information
-Might have emotional significance
-Opportunity for rehearsal- daily contact
-Same is not true for other types of information-findings on VLTM cannot be generalised to other types of information.
- Compared to majority of other research-takes place in laboratory-research has mundane realism, real-life memory.
-Represents natural behaviour-high ecological validity.
-Possible to generalise findings to other settings.
