Experiments - Multi store model of memory.

Research:

Supporting and conflicting:

27year old suffering severe epilepsy.

Surgeons carried out drastic operations to remove most of his hippocampus.

Memory was affected – he could remember most events before the operation but none after. He was unable to make new LTM.

Both episodic and semantic memories were damaged.

Although he could not remember what he had for breakfast, he learnt how to play tennis.

The part of his brain concerned with procedural memories (cerebellum) was not affected.

Milner discovered that HM was able to learn to trace a shape using its mirror image and retain this skill over a number of days. He had no conscious recollection of having done the mirror drawing task.

It appears the HM was able to use procedural memory to learn the skill, but his operation had damaged his ability to use his declarative memory to consciously recollect this experience.

Supports STM + LTM are two separate stores. (STM intact, unable to form new LTM).

Challanges MSM LTM is no 1 unitary store - (unable to use declarative memory but can use procedural memory).

Evidence for separate episodic and semantic memories:

Tulving:

Heindel et al:

Tulving performed brain scans on six volunteers and found that when the P’s were using their episodic memory part of the front cortex (frontal lobes) was active compared to when P’ were using their semantic memory when the back cortex was active.

This supports the notion that episodic memory and semantic memory are two separate systems (although both are types of declarative memory.

Investigated learning in people with Huntington disease a progressive degenerative disease of the brain. They found that HD patients had no problems learning new facts and knowledge but had severe problems learning new motor skills. This shows that procedural and semantic memories are two separate systems.

Jacobs (Experiment short term memory – Capacity)

Conclusions:

Short term memory has limited capacity 5-9 items.

He also found numbers are easier to recall than letters as there are fewer of them, 9 compared to 25.

Evaluation:

One limitation of Jacobs study is that it was conducted a long time ago.

Early research in psychology often lacked adequate control.

For example, some P’s may have been distracted while they were being tested.

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

However, the results of this study have been confirmed in other research which supports its validity and increases its reliability.

Miller (Experiment short term memory – Capacity)

Miller coined the phrase ‘the magic number 7 + or _ 2’ to describe the capacity of STM.

Miller believed that our immediate memory span is determined by the number of chunks of information we can hold rather than the number of individual letters or numbers.

He noted that things come in sevens: there are seven notes on the music scale, 7 days of the week, 7 deadly sins, and so on, this suggests the span or capacity of STM is about 7 items.

However, miller also noted that people can recall 5 words as well as they can recall 5 letters. They do this by chunking grouping sets of digits or letters into units or chunks.

i.e. learning a mobile number in groups of 3 numbers.

Millor thought that the chunk was the basic unit in STM and that we can remember 7+/-2 chunks of information at any one time.

Other researchers criticize the term chunk as being too vague.

Cowan reviewed research and concluded that the capacity of STM.

Peterson & Peterson (Experiment on STM Duration)

Evaluation:

Got students to recall combinations of 3 letters (trigrams), after longer and longer intervals.

During the intervals students were prevented from rehearsing by a counting task.

Lacks Mundane realism

Lacks external validity – doesn't reflect most real-life memory activities.

However, we do sometimes try to remember phone numbers so the study isn't totally irrelevant.

Could have been a capacity issue rather than a duration issue.

Baddeley (experiment on STM encoding)

Group one: Acoustically similar (e.g. man, cab, can, cat).

Group two: Acoustically dissimilar (e.g. pit, few, cow, pen).

Group three: Semantically similar (e.g. great, large, big, huge).

Group four: Semantically dissimilar (e.g. good, huge, hot, safe).

Results:

The list of words was read out to them and then they were asked to immediately recall them. They found that G1 performed the worst. This led Baddeley to conclude that STM is predominately encoded acoustically.

Conrad (experiment on STM encoding)

Findings

Evaluation

Showed P’s a random sequence of six consonants.

He projected them in a very rapid sequence onto a screen.

There were two conditions in his study.

Acoustically similar (BGCTDV)

Acoustically dissimilar (FJXMSR)

Afterwards P’s asked to immediately after the presentation to write the letters down in the correct order.

Normal digit span is about 7.

However, Conrad found P’s frequently made errors of recall and most errors involved the substitution of similar sounding letters. E.g. V for a D

P’s found it more difficult to recall strings of letters that sounded the same (acoustic confusion)

This supports the theory that encoding is acoustic in STM

Conrad concluded that while the consonant sequences had been presented visually, the P’s had converted them to an acoustic code in STM.

It was this encoding that resulted in the difficulties distinguishing between constants that sounded similar.

This was a very well controlled lab experiment however it used artificial stimuli and students – lacks external validity.

Unsing students means it lacks population validity.

Another research suggested that it is too simplistic.

KF Case study (encoding STM)

They found KF’s STM for digits was very poor when they read them out loud to him (acoustic), but his recall was much better when he was able to read the digits himself (visual).

Further studies of KF and others showed there could even be another short-term store for non-verbal sounds.

The unitary STM is a limitation of the MSM.

Research suggests there must be one short term memory store to process visual information and another to process auditory information.

Baddeley (experiment on LTM encoding)

Same people recall lists but 20 mins later.

This time they found that group three performed the worst.

This led Baddeley to conclude that long term memory is predominantly encoded semantically. The meaning-based encoding semantically.

Bahrisk et al. (experiment on LTM Duration)

392 high school graduates from the state of Ohio, USA aged from 17-74. Their LTM was tested in the form of the names and pictures of their classmates taken from their high school yearbooks.

Results – Photo recognition:

Graduated high school within the last 15 years – 90% accurate.

Graduated 48 years ago –70% accurate.

This study demonstrated how a person's memory can last for a very long time – a person's lifetime.

Table summary:

	Coding	Capacity	Duration	Forgetting
Sensory register	Multi-sensory Modality specific Iconic = Visual Echoic = Auditory	Unlimited	Very short time (2 - 3 seconds)	Displacement.
Short-term memory	Acoustically (Baddeley, 1966)	Very limited - 7 +/-2 items (Miller, 1956)	15-30 seconds (Peterson & Peterson, 1959)	Mainly displacement (Miller 7 +/- 2)
Long term memory	Semantically (Baddeley 1966)	Unlimited	Lifetime; potentially forever (Banrick et al. 1975)	Mainly interference (Peterson & Peterson)