Evidence for Sensory Memory.
- Participant's saw a grid of digits and letters for 50 milliseconds.
- They were asked to either write down all 12 items or they were told they would hear a tone immediately after exposure and they should just write the corresponding row.
- When asked to report the whole thing their recall was poorer (42%) than when asked to give just a row (75%)
- This shows that information decays rapidly in the sensory store and therefore supports the Multi Store Model.
1 of 9
Capacity of STM.
- A lab experiment using the digit-span technique was conducted. Pt's were presented with a sequence of letters or digits, followed by serial recall.
- The pace of the item presentation was controlled to half-second intervals through a metronome. Initally, the sequence was 3 items, which then increased by a single item until the participant consistently failed to produce the sequence correctly. This was repeated over a number of trials to establish the pt's digit (or letter) span.
- Jacobs found that the average STM span was between 5 and 9 items. Digits were recalled better (9 items) than letters (7 items). Individual differences were found, hence the range 5-9. Furthermore, the STM span increased with age.
- The experiment uses the scientific method eg. the effect of the IV on the DV can be accurately measured. Extraneous variables can be controlled.
- Research into STM and LTM has practical applications - findings relating to the capacity of STM has been usefully applied to improve memory.
- The research is useful because memory improvement techniques are based on the findings that the digit span cannot be increased by the size of the bits can be eg. chunking.
- Lacks ecological validity & mundane realism.
2 of 9
Duration of STM.
The Brown-Peterson technique:
- Participants hear various trigrams. Immediately afterwards, they are instructed to recall what they heard or count backwards in 3's out loud from some specified number for a pre-determined period of time (the retention interval). The function of this distractor time is to prevent rehearsal. At the end of the time period pt's try to recall the trigram.
- The average percentage of correctly recalled trigrams was high with short delays but decreased as the delay interval lengthened - on average, 18 seconds.
- The research used scientific methods; the effect of the IV on the DV can be accurately measured and extraneous variables controlled.
- The sample was biased - they were all American students therefore we may not have population validity.
- The research lacked mundane realism - artificial stimuli and trying to memorise trigrams is not an every day task.
- The research also lacked ecological validity - the environment in which the research was conducted was artificial.
- Ethics - consent, withdrawal.
3 of 9
The serial position effect:
- Murdock presented pt's with a list of words at a rate of about one per second. They were required to free recall as many of these things as they could. It was found that the probability of recalling any word depended on it's position in the list.
- Pt's recalled those items from the end of the list first, and got more of these correct then the earlier items. Items from the beginning were also recalled well relative to those in the middle. This is the PRIMARY-RECENCY EFFECT.
- The items at the beginning of the list would have been rehearsed and items at the end would still be in the STM.
- This study therefore supports the MSM because it suggests that STM and LTM are seperate.
4 of 9
HM - case study for evidence of separate stores.
- A surgeon tried to cure HM's epilepsy by cutting a hole in his head and sucked part of his brain out through a silver straw. He removed the hippocampus and therefore HM lost the ability to encode new memories.
- He was stuck in the past and the present with no future to look forward to. He still had his normal STM - he could repeat lists of numbers or letters just heard.
- He was aware of what happened a minute or so ago but beyond this or if he was distracted, he could recall nothing.
- He was incapable of updating his LTM.
- As these are case studies of one person, you can't generalise the findings to the rest of the population, they lack population validity.
- On the other hand, because they are on an individual, they are rich in detail.
- As these are real life case studies, they are high in ecological validity.
5 of 9
Capacity of LTM.
Case study of Solomon Shereshevsky:
- Solomon Shereshevsky was said to have the best ever memory. He was studied by a professor for over 30 years. It is claimed that Shereshevsky's memory was so perfect that he could remember virtually every detail of his life in the most minute detail.
- When Luria first met Shereshevsky and gave him a long list of numbers, worse and nonsense syllables to remember, all were recalled perfectly.
- Luria could find no limit to the capacity or duration of his memory. Shereshevsky started to perform his memory deats on stage; for a time earning his living as a mnemonist, demonstrating his remarkable prowess.
- This case study supports the MSM by suggesting that the LTM has an unlimited capacity and can store for up to a lifetime.
6 of 9
Duration of LTM.
- 392 American ex-high school students aged 12-74. Recall was tested in 4 ways:
- Free recall of the names of as many of their former classmates as possible.
- A photo recognition test where they were asked to identify former classmates in a set of 50 photos, only some of which were their classmates.
- A name recognition test.
- A name and photo matching test.
- 90% accuracy in face recognition of their former classmates, even in the partipants who had left school 34 years previously.
- After 48 years, the recall declined to 80% for name recognition and 40% for face recognition.
- Free recall was considerably less accurate.
- The findings showed that memory may not be as unreliable as is commonly percieved. However, the research is aimed at very specific information - faces and names of people who had been seen on a regular basis over a period of time.
- Overall, Bahrick's results suppport the MSM in the duration of LTM being up to a lifetime.
7 of 9
Evaluation of Bahrick's study.
- Bahrick's research has high mundane realism - asking participants to recall their classmakes tests a real life memory. The research is therefore more representative of natural behaviour (how an individual spontaneously recalls information over a very long period of time) and so has high ecological validity.
- Classmates faces are a very particular type of information, they may have en emotional significance and due to daily contact there will have been lots of opportunity for rehearsal. This is not the same for other types of information so these findings related to the duration of LTM cannot be generalised to other types of information.
- Biased sample as it only tested American ex-high school students.
8 of 9
General evaluation for the MSM.
- The MSM provides a systematic account of the structures and processes involved in human memory. Backed up by considerable evidence.
- Case studies of brain damaged patients also support the distinction between short term and long term memory srotes.
- The existence of seperate stores is supported by the use of brain scanning techniques eg. PET scans.
- The MSM states you have to rehearse info to transfer it to LTM. From real life examples we know this isn't correct. We read/see something once and it's remembered for hours but struggle to remember something for an exam. The theory of a 'flashbulb' memory is also evidence against the MSM.
- The MSM is sometimes seen as an oversimplification of memory eg. Clive Wearing couldn't remember his personal history but could still conduct an orchestra - suggesting there's more than one long term store.
- The MSM suggest STM is a single store - again research such as KF suggest that there are several components to STM. Also the WMM disputes the idea of a single store for STM.
9 of 9