Tuesday, 18 March 2014

Memory Capacity Revision

It is generally accepted that LTM has an unlimited capacity. It is possible to lose things through processes such as decay and interference but the loss does not occur because of capacity limitations.

Researchers generally agree that STM has a limited capacity. If someone gives you a phone number to remember, it is impossible to recall it without rehearsal because STM has a limited capacity and items can get displaced. 

Jacobs devised one of the earliest attempts at measure the capacity of STM in 1887 called the digit span technique*. Jacobs found that on average, people could recall about 7 digits in this immediate serial recall task*.

George Miller
Wrote a famous article in 1956, called 'The Magical Number 7, Plus or Minus 2' in which he proposed that we can hold about 7 items in our STM, but there is a range of capacity between 5 and 9 items. 
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 numerals. 
Also, memory span can be increased by chunking. 

Some psychologists have criticised Miller's concept of chunking for being too vague. Simon (1974) found that the span as measured in chunks depends on the amount of information contained in the chunk. He experimented with the immediate serial recall technique with one-syllable, two-syllable and three syllable, and for two and eight word phrases. 
He found that the span in chunks was less with larger chunks, i.e eight word phrases, than with smaller chunks. 

Glanzer and Razel (1974) used the recency effect rather than the digit span as a measure of the capacity of STM. They found that the recency effect 2.2 items when the stimulus material consisted of single, unrelated words, but increased to 1.5 sentences (i.e considerably more single words) when unfamiliar sentences were presented and to 2.2 proverbs when familiar proverbs (e.g. 'a stich in time saves nine') were used. 

Saturday, 8 March 2014

Neuropsychological Evidence for Differences Between STM and LTM

Some evidence for the difference between STM and LTM comes from case studies of people who have suffered brain damage. In these cases memory is selective; it affects one type of memory but not the other. 

Clive Wearing 
Wearing has an impaired short term memory and has a poor duration that can only hold information for 7 seconds (the average person has a duration of 18-30 seconds). Since his illness he cannot create any new memories and constantly feels like he has awoke from unconsciousness. Wearing contracted a form of amnesia after a herpes simplex (cold sore) spread to areas of his temporal lobes. 

Henry Molaison 
HM suffered from epilepsy and as a result underwent brain surgery to remove part of his temporal lobes and hippocampus. This alleviated his epilepsy but left him with severe memory deficits although his IQ remained above average. He was able to recall events in his early life but was unable to remember events for about 10 years before the surgery and could not learn or retain new information. He could remember approximately six numbers in the order they were presented suggesting his STM was okay. However, he would read the same magazine over and over again and not process the information into LTM, not realizing he had read it before. He was also unable to recognise psychologists who sent long periods of time with him. HM suffered from anterograde amnesia (the loss of ability to create new memories).

In both of these cases, episodic memory (the memory of autobiographical events times, places, associated emotions, and other contextual who, what, when, where, why knowledge that can be explicitly state) is lost. However Semantic memory ( which refers to the memory of meanings, understandings, and other concept-based knowledge, and underlies the conscious recollection of factual information and general knowledge about the world) is largely unaffected 

KF sustained brain injuries after a motorcycle accident. He appeared to have an intact LTM store in that he was able to learn new information and recall stored information. However, his STM was affected so that he had a recency effect of only one item. Also, although his visual information was on a normal level, he struggled with auditory and verbal information making conversation difficult. 

Alzeihmer's Patients
Patients with Alzheimer's disease have been found to have  low levels of a neurotransmitter acetylcholine. Drachman and Sahakian (1979) investigated this by administering a drug to a group of participants which blocks the action of acetylcholine in the brain. They then gave participants various memory tasks that tested either STM or LTM and compared their performance with a control group. They found that the experimental group performed normally on STM tasks but significantly more poorly in the LTM task.

Squire et al. found that the hippocampus is active in LTM tasks whereas areas in the prefrontal cortex are activated for STM tasks. 

Conclusions: what does this tell us?
-Amnesiacs tend to lose only one store suggesting that LTM and STM are separate
-However, it is more complicated as LTM seems to consist of more than one component (semantic and episodic). Plus, KF's case seems to suggest that STM is more complex than a single store.

Friday, 7 March 2014

The Distinction Between STM and LTM

When psychologists use the free recall technique it produces a characteristic serial curve. This is thought to be because words at the beginning of a list have been rehearsed and have passed to LTM meaning they can be recalled at the time of rehearsal (the Primacy effect). Words at the end are still circulating in STM and can be easily retrieved (recency effect). While words in the middle have had little time for rehearsal and have been displaced by later items in the list (asymptote) Glanzer and Cunitz (1966) showed this functional dissociation in their experiment. 

Glanzer and Cunitz (1966)
Aim: To find functional dissociation curve in STM and LTM
Procedure: There were two conditions in the experiment
- In Condition One, participants were asked to recall the words immediately after they had been presented
-In Condition Two, participants were given a distractor task after the words had been presented and had to count backwards in 3s for 30 seconds before they were asked to recall words. 
Results:In condition one they found the expected serial position curve. However, in condition 2, they found that the distractor task had been disrupted the recency effect and words from the last part of the list were not recalled well. 
Conclusions: They explained that the task of counting backwards had displaced the last few words in the list from the fragile STM but the task had not affected earlier words because they had been rehearsed and passed to LTM
Evaluation: Lab so highly controlled. However, does not represent how memory works in daily life. 
Researchers had to gain consent and debrief them afterwards so was ethical

Sensory Memory Revision

Sensory Memory act as a filter with each sense having its own brief storage system. Few if any will be remembered. Right now you are reading and this is a visual environmental stimuli. It appears to hold information for a fraction of a second and unless the information is unusual in anyway will not be recalled. However, if it is unusual it will be transferred to the short term memory store. Sensory memory therefore plays a vital role in filtering out the vast majority of useless stuff that impinges on our senses and enables us to focus our attention on important detail. 

Sperling (1960) 

Aim: To explore the capacity of sensory memory.
Procedure: Participants were asked to look at a chart for 50 milliseconds and were asked to freely recall any letters they remembered. They could usually recall 4 or 5 items.
In the second stage participants were asked to recall single rows when particular tones were heard (high for top row, middle tone for the middle tow and low tone for the bottom).
ResultsIn the second condition, participants were able to recall on average 3 items from whichever row was cued by the tone.
Conclusions:  Although in theory P's should remember more than the average 4 items, it is thought that the image of each item fades during the 50ms and the time it takes to report back recalled items. Therefore, sensory memory has a large capacity but most items fade before they can be processed.
Evaluation: Methodological: Lab high level of control, and replicable.

-items remain in sensory memory for a very brief period of time probably less than two seconds (or even less in the iconic store). 
-Information is in a relatively unprocessed form. It’s passively registered in sensory memory, we can’t control what enters it but we can actively select certain items for transmission to short term memory by paying attention to them. 
-There are different stores for different parts: iconic for visual, echoic for sound and haptic store for things we feel touch.