Short term memory was description by Atkinson & Shiffin in their modal model of memory in which they explained that information in STM lasts only for a very limited that is for about 15-30 seconds. In order to explain the methodology of STM, Brown/ Peterson & Peterson have conducted a study in which participants were asked to study 3 letters. Then they were asked to count backward by 3’s. eg: 100, 97, 94, 91, 88… for short period of time and later were asked to recall the letters they had originally seen. The result revealed for the 1st few trials show that people recalled most of the letters, however after several trials, the previous learnt letters produce interference and thus recall was poor. More ever after 5 seconds delay, people forgot approximately half of what they had seen.
Other techniques also have been used to examine short term memory. One among it is people were asked to study a long list of items such a many words as possible. The result reveled that there existed relationship between the position of the word presented and the probability of recalling the word which was termed as serial position curve/ effect.
Eg: recalling is accurate for the beginning & end words where as it was poor recall for the middle words some researches views that people were able to recall last words more accurately because the words were still in the STM at the time of recalling.
The size of STM
One way of measuring the size of STM is to count the no of word accurately recalled at eh end of the list typically the size of STM is estimated to be 2-7 items when the serial – position curve method is used.
STM size is measured in terms if memory span or the number if items in a row that can be correctly recalled. However, some researches view that pronunciation time is an important determination of STM. More over factors such as anxiety also influences the number of items that could be held in temporary storage.
Miller’s Magical Numbers:-
In 1956 George Miller wrote a famous article title. The magical number Severn plus or Minus two
Eg: some limits on our capacity for processing information. Miller proposed that people cannot keep many items in STM has 5 & 9 items. i.e- 7+2 based on the capacity of an individual. He used the term chunk to describe the basic unit of the STM. Chunk is single numeral or a single letter. How ever of the items are larger in the size than Miller proposed that we divide the items into smaller units and each unit is called as one chunk. Eg: 9844362753 is a larger item which could be remembered by dividing it into 3 smaller chunks. Eg: 9844-362-753.
Though Miller’s work gained major attention initially, psychologists such as Simon complained that major problems of chunk is that it is a legitimate concept because it is closely related to learning time and hence it is not arbitrary term describing the seven units in memory.
Pronunciation time (for each word)
Some psychologists give importance to pronunciation time than number of chunks forms in the items. Schweickert & Boruff (1986) tested memory span for a variety of material such as consonants, numbers, nouns, shapes, name of colors, nonsense words etc which were pronounced within 1.5 seconds. The result of their study revealed that for English language and easy terms around 6 items were recalled where as for nonsense syllable only 4 items were recalled within the given 1.5 seconds as pronunciation time.
Anxiety and Memory Span
Researches have proved that highly anxious people have shorter memory than led anxious people. Darke (1988) conducted an experiment in which he administered anxiety scale on a group of English speaking college students and selected students who scored high socres and low scores on anxiety. Later he administered them with a memory test. Result of his test revealed that students with high anxiety level recalled an average of 8.8 no’s and students with low level of anxiety were able to recall an average of 10.4 no’s which clearly indicates the negative relation between anxiety and memory span. This is one of the reason that students who are highly anxious perform poorly in examination as their anxiety limits their memory span.
Coding in short term memory
Postman (1975) and Corowder (1982) viewed that apart from acoustic coding, information in the STM could be coded visually as well as semantically also.
Researches have tired to understand the efficiency level between three types of coding in the STM namely acoustic coding, Visual coding and semantic coding.
1. Acoustic coding & STM
Many studies have been conducted to understand the acoustic coding in STM. Among them one of the study was conducted by Wicke;lgren (1965). He presented a tape to his subject which consisted of 8 items list among which four letters and four digits were presented in random order. Eg: 4NG9G27P. as soon as the tape was finished, subjects were asked to recall the list, wickelgran was particularly interested to know the kinds of substitutions people made. Eg: they did not recall the last letter P correctly, instead they substituted an item which was acoustically similar such as B,C,D,E,G,T ( all letters with “ee’ sound. Furthermore they substituted a no then it was 3 )
Brandimonte and her colleagues (1992) viewed that then acoustic coding in STM can have an important effect on long term memory. To explain this they conducted an experiment in which they compared the performance of 3 groups of participants. The participants were shuffled into control group and experimental group. In 1st trial the participants of control were asked to see 6 pictures of objects, such as a figure of a candy. Or a pipe etc which ere named as original pictures. The observations were repeated until participants knew the order of the picture. In the second series they were asked to create a mental image of each picture they were observed and they were also asked to subtract a specific part from each image to report the resulting image. Eg: after creating the mental image of the piece of candy and subtracting part they reported is as a bowl. The participants in the control condition succeeded in naming an average of 2.7 items correctly out of maximum 6.0 items.
2. Visual coding & STM
Posner and Keele (1967) have illustrated visual coding in STM very convincingly. In their experiment people were showed pains of letters such as AA, Aa, AB, Ab etc… and were asked to answer whether the letters had identical names or not. Sometimes the 2 letters were presented at the same time and sometimes there was briefly delay in exposure between the 2 letters.
Posner and Keele were interested to see whether people took linger time to respond yes to Aa pains than AA pairs as they viewed if the pains were stored merely in terms of the sounds by the participants then the response time for both the pairs should be same and if items were stored in terms f the way they look then the time of response for Aa pairs should be longer then for AA pair. Because, the visual symbol must be translated into appropriate names.
The result revealed that when the delay if exposure between the 2 letters were less than 1.5 sec, than the response time for Aa pair was longer than for AA pain and if the delay of exposure was longer than 1.5 sec then both the pairs were responded in same amount of time. This is because initially the participants coded the pair in terms of physical appearance, but later i.e: after 1.5 sec Aa pairs and AA pairs took same amount of time as they were coded in terms of identical letter name. thus they concluded that visual code can be stored in STM for very brief periods but these visual codes are very fragile and are soon replaced by auditory code.
3. Semantic coding in STM
Wickens and his colleagues have conducted an experiment to show semantic coding system in STM. Their technique was based on the concept of proactive inhibition, which means people have trouble in learning new material because the previously learned material interferes with new learning. Eg: if u have learnt the items XCI. HBR and TVS in a test of STM, you may have troubled in learning a fourth item KRN, because the previously learned items interfere. However in the experimenter changes the items from letter to numbers then, learning is almost high as it will be for the 1st time.
Wickens and his colleagues demonstrated that release from proactive inhibition (PI) can be obtained even if the semantic class of the items were changed. That explains this Wickens conducted an experiment in which he presented 3 trials of fruits for 5 groups of students, ie: each group of student in the 1st trial were presented 3 groups of fruits . eg: (apple, banana, peach ), (plum, apricot, lime), (melon, lemon, grapes). In the 2nd trial the materials were shifted to vegetables, flowers , meats, profession and fruits.
The 1st group of students were presented with 3 groups fruits in the 3rd trial and on the fourth trial they were again presented 3 groups of fruits and then after a gap of 18 seconds in which they had to count the numbers back from 3’s and they asked to recall the presented items. Similarly the 2nd group of students were presented 3 groups of fruits for 3 trials and in the 4th trial they presented with 3 groups of vegetables, again after the gap of 18 sec in which they has to count backward from 3’s and they were asked to recall the presented items.
In the same manner the 3rd group of students were presented with 3 groups of flowers. 4th groups were presented 3 groups of meat and the 5th group were presented with 3 groups of professions such as (doctor, teacher, lawyer) and the recalling capacity was checked. The result of this experiment revealed that the recalling was best in the case of 5th group of students who were presented with professions in their 4th trial and recalling of 3rd, 4th group who were presented with flowers and meat was somewhat better than the 1st two groups who were presented with fruits and vegetables. After these 2 groups performed very poorly in their 4th trial.
Wickens concludes that fruits and vegetables resemble very much to each other as both are eatables and grow on the ground. So that learning was effected by proactive inhibition and that for the 5th group who were presented with profession, learning was best as the meaning of fruits and profession differ a lot. Thus meaning is important in STM.
Working memory – A new view of short term memory
Alan Baddeley has developed the most complete description of multi component interpretation of STM which he calls as working memory. According to Baddeley working memory is a 3-part system that temporarily holds and manipulates information as we perform cognitive task. ( note ; Baddeley felt that working memory is just like a work bench where materials constantly being handled combined and transformed ).
The 3 components are phological loop, Visuospatial sketch pan and central executive.
a) Phonological loop (LP)
According to Baddeley’s model, the phonological loop stories a limited number of sounds for a very short span of 2 seconds unless the material is rehearsed. Material in Phonological loop are coded acoustically, hence items that sounds same are confused with one another and are more readily forgotten.
b) Viscouspatial sketch pad ( VSP).
This is the 2nd component of working memory which stores visual and spatial information like Phonological loop. The capacity of viscouspatial sketch pad is limited. However the limits of PL & VSP are independent.
c) Central Executive (CE)
According to Baddeley’s model , the CE integrates information from the PL and the VSP as well as from the long term memory. It also plays a major role in attention and panning a controlling behavior Baddeley views that CE works like a supervisor or schedules. It decides which issue deserves attention and which should be ignored. It also selects strategies figuring out how to tackle a problem etc. however Baddley admits that is is difficult to study CE even with new scientific research techniques.
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