Capacity, Coding and Duration

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  • Coding, Capacity and Duration.
    • Research on Coding.
      • Once information gets into the memory system, it is stored in different formats
      • The process of converting information from one form to another is called coding.
      • 4 groups: 1= Acoustically similar words
        • 2= Acoustically dissimilar words.
        • 3= Semantically similar words
        • 4= Semantically dissimilar words.
      • Participants were shown the original words and asked to recall them, when they had to recall it from STM they tended to do worse with acoustically similar words
        • If participants were asked to recall the word list after 20 mins LTM they tended to do worse with the semantically similar words. This suggest that information is coded semantically in LTM.
    • Research on capacity
      • Digital Span- How much information can STM hold at any one time. Joseph Jacobs developed a technique to measure digit span.
        • The researcher gives 4 digits for example and is asked to recall them in the correct order out loud. If this is correct the researcher reads out 5 digits and so on until participants cannot recall it correctly.
          • This determines the individual's digit span. Jacobs found that the mean span for digits across all participants was 9.3 items. The mean span for letters was 7.3
      • Span of memory and chunking- George Miller made observations of everyday practice. He noticed that things come in sevens
        • This suggest that the span of STM is about 7 items (Plus or minus 2) 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
    • Research on duration
      • Duration of STM
        • Duration is the defining feature of STM. Margaret and Llyod Peterson tested 24 undergraduate students. Each student took part in eight trials.
          • A 'trial' is one test. On each trial the student was given a consonant syllable to remember and was also given a 3-digit number. The student was then asked to count backwards from that 3-digit number until told to stop
            • This counting backwards was to prevent any mental rehearsal of the consonant syllable. On each trial they were told to stop after a different amount of time- 3,6,9,12,15 or 18 seconds
              • This is called the retention interval. It suggests that STM may have a very short duration, unless we repeat something over and over again.
      • Duration of LTM
        • Harry Bahrick et al studied 392 participants from the American state of Ohio who were aged between 17 and 74. High school yearbooks were obtained from the participants or directly from some schools
          • Recall was tested in various ways, including; 1) photo-recognition test consisting of 50 photos, some from the participants high school yearbook
            • 2) Free recall test where participants recalled all the names of their graduating class. Participants who were tested within 15 years of graduation were about 90% accurate in photo recognition
              • After 48 years, recall declined to about 70% for photo recognition. Free recall was less good than recognition.
                • After 15 years this was about 60% accurate dropping to 30% after 48 years.  This shows that LTM can last a very long time

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