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Lecture 4 Memory Memory is a hypothetical construct denoting 3 distinguishable but interrelated processes:
1. Registration (or encoding)- the transformation of sensory input e.g. sound or visual image into a form that allows it to be entered into or registered into the memory.
2. Storage- the operation of holding or retaining information in memory. In humans, the changes that occur in the brain allow information to be stored.
3. Retrieval- the process by which stored information is extracted from the memory. Not everything that registers on the senses is actually stored in the memory. Similarly, we cannot retrieve information that hasn't been stored but at the same time, the fact that it has been stored doesn't mean that we will be able to retrieve it. This is the crucial distinction between availability (whether or not the information has been stored) and accessibility (whether or not it can be retrieved), which is relevant in theories of forgetting. When people complain about having poor memory, this could be either storage or retrieval but they aren't able to make the distinction. Sensory memory Sensory memory gives us an accurate account of the environment as experienced by the sensory system. Storage => Sensory memory => Short term memory (STM) => Long term memory (LTM) We retain a literal copy of the stimulus for long enough for us to decide whether it is worthy of further processing. Any information we don't attend to process further is forgotten. Short term memory (STM) Probably less than 1/100th of all the sensory information that impinges on the human senses every second reaches our consciousness and only 5% or so of this is stored permanently. If we only processed sensory memory, our capacity for retaining information about the world would be extremely limited. However, according to memory models such Atkinson and Shiffrin's multi store model, some information from sensory memory is successfully passed on to short term memory. STM and LTM can be analysed in terms of :
Capacity- how much information can be stored
Duration- how long the information can be held in storage
Coding- how sensory input is represented by the memory system
Capacity Ebbinghaus and Wundt were two of the first psychologists to maintain that STM is limited to 6 or 7 bits of information. The most famous account is given by Miller (1956). He showed how chunking can be used to expand the limited capacity of STM by using already established memory stores to categorise new information. Chunking If we think of STM's capacity as 7 slots with each slot being able to accommodate one bit or unit of information, then 7 individual letters would each fill a slot and there'd be no room left for any additional
letters. If the letters are chunked into a word, then the word would constitute one unit of information, leaving 6 free slots. To be able to chunk, you have to know the rule or the code. Chunking is involved whenever we reduce a larger amount of information into a smaller amount. This a) increases the capacity of the STM and b) represents a form of encoding information by imposing a meaning on otherwise meaningless information. For example, arranging letters into words, words into phrases, phrases into sentences. Although the amount of information contained in any one unit is unlimited, the number of chunks that can be held in STM is still limited to 7 plus or minus 2. Duration A way of studying pure STM was devised by Brown (1958) and Peterson and Peterson (19590 and is called the Brown-Peterson technique. By repeating something that has to be remembered (maintenance rehearsal), information can be held in STM almost indefinitely. The Brown- Peterson technique overcomes this problem (see textbook p259) Coding Conrad (1964) presented participants visually with a list of 6 consonants each of which was seen for about 3/4 of a second. They were instructed to write down the consonants. Mistakes tended to be related to a letter's sound. For example, there were 62 instances of B being mistaken for P, 83 instances of V being mistaken for P but only 2 cases of S being mistaken for P. These acoustic confusion errors suggested to Conrad that STM must code information according to its sound. Even when information is presented visually, it must be somehow transformed into its acoustic code. Long term memory (LTM) Capacity and duration It is generally accepted that LTM has unlimited capacity. It can be thought of as a vast store house of all the information, skills, abilities and so on which aren't currently being used but are potentially retrievable. According to Bower (1975), some of the information contained in LTM include:
A spatial model of the world around us.
Knowledge of the physical world around us, physical laws and properties of objects.
Beliefs about people, ourselves, social norms, values and goals.
Motor skills, problem solving skills and plans for achieving various things.
Perceptual skills in understanding language, interpreting music and so on.
Information can be held from between a few minutes and several years (and may in fact span the individual's entire lifetime). Coding With verbal material, coding in LTM appears to be mainly semantic. For example, Baddeley (1966) presented participants with words which were either:
Acoustically similar e.g. caught, short, taut
Semantically similar e.g. huge, great, big, wide
Acoustically dissimilar e.g. foul, old, creepy
Semantically dissimilar e.g. pen, day, ring
When recall from STM as tested, acoustically similar words were recalled less well than acoustically dissimilar words. This supports the claim that acoustic coding occurs in STM. There was a small difference between the semantically similar and semantically dissimilar words recalled. This suggests that whilst semantic coding occurs, it is not the dominant type of coding. When a similar study was carried out in LTM, fewer semantically similar words were recalled while acoustically similar words had no effect. This suggests that LTM's dominant coding is semantic. Similarly, it was found that immediate recall of the order of short lists of unrelated words was seriously impeded if the words were acoustically similar but not if they were semantically similar. After a delay however, the exact opposite occurred. Retrieval There are many different ways of recovering information that has been stored. Pure memory (Ebbinghaus, 1885) To study memory in its purest form, Ebbinghaus invented 3 letter nonsense syllables e.g. XUT, JEQ. He spent several years using only himself as the subject of his research. He read lists of nonsense syllables out loud and when he felt he'd recited a list sufficiently to retain it, he tested himself. If he could recite a list twice in succession, he considered it to be learned. After recording the time taken to learn a list, he began another one. After specific periods of time, he'd return to a particular list and try to memorise it again. He calculated the number of attempts (or trials) it took him to relearn the list as a percentage of the number of trials it had originally taken to learn it. He found that memory declines sharply at first but then levels off.
Thus, MOST OF THE MEMORRY LOSS OCCURRED WITHIN THE FIRST MINUTES AFTER TRAINING: ONCE MEMORY HAD SURVIVED THIS HURDLE, IT SEEMED MUCH MORE STABLE.
Other techniques for measuring memory
1. Recognition : This involves deciding whether a piece of information has been encountered before e.g. in an MCQ exam.
2. Recall: This involves participants actively searching their memory stores in order to retrieve particular information e.g. in timed essays. The material can either be recalled in the order in which it was presented (serial recall) or in any order at all (free recall).
3. Memory span procedure: This is a version of serial recall in which the person is given a list of un related digits or letters and then required to repeat them immediately in the order in which they were heard. The number of items on the list is increased until an error is made. The maximum number of items which can be recalled correctly is a measure of immediate memory span.
4. Paired associates recall: Participants are required to learn a list of paired items e.g. chair and elephant. When one of the words e.g. chair is re presented, the participant must recall the paired word e.g. elephant. Multi- store model (MSM) Atkinson and Shiffinrin's MSM was an attempt to explain how information flows from one storage system to another. The model sees STM and LTM as important parts of the system. In addition to this, the memory system comprises of more transient control processes of which rehearsal is key. Rehearsal serves 2 main functions:
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