Coding, Capacity And Duration Of Memory Flashcards
Research on coding
Information is stored in memory in different forms, depending on the memory store. The process of converting information between different forms is called coding.
Alan Baddeley (1966a,1966b) gave different lists of words to four groups of participants to remember:
-group 1 (acoustically similar):words sounded similar (cat, can)
-group 2 (acoustically dissimilar): words sounded different (eg pit, few)
-group 3 (semantically similar): words with similar meanings (great, large)
-group 4 (semantically dissimilar): words with different meanings (good, huge)
Participants were shown the original words and asked to recall them in the correct order. When they did this task immediately, recalling from short term memory (STM) they tended to do worse with acoustically similar words. When they recalled the word list after a time interval of 20 minutes, recalling from LTM, they did worse with semantically similar words. These findings suggest that information is coded acoustically in STM and semantically in LTM.
Research on capacity-digital span
How much information can STM hold at one time-what is its capacity? Joseph Jacob’s (1887) found out by measuring digit span. For example, the researcher reads out four digits and the participant recalls these out loud in the correct order. If this is correct the researcher reads out five digits and so on until the participant cannot recall the order correctly. This indicates the individuals digit span.
Jacob’s found that the mean span for digits across all participants was 9.3 items. The mean span for letters was 7.3
Research on capacity-span of memory and chunking
George Miller (1956) made observations of everyday practice. For example, he noted that things come in sevens:seven notes on the musical scale, seven days of the week. Miller thought that the span (i.e. capacity) of STM is about 7 items, plus or minus 2. But he also noted that people can recall five words as easily as they can recall five letters. We do this by chunking-grouping sets of digits or letters into units or chunks.
Research on duration-duration of the STM
How short is the duration on STM? Margaret and Lloyd Peterson (1959) tested 24 students in eight trials each (a ‘trial’ is one test). On each trial the student was given a consonant syllable (such as YCG) to remember. They were also given a 3-digit number. The student counted backwards from this number until told to stop. The counting backwards was to prevent any mental rehearsal of the consonant syllable (which would increase the duration of STM memory for the syllable).
On each trial they were told to stop after varying periods of time: 3,6,9,12,15 or 18 seconds (the retention interval). After 3 seconds, average recall was about 80%, after 18 seconds it was about 3%. Peterson and Petersons findings suggested that STM duration may be about 18 seconds, unless we repeat the information over and over (ie verbal rehearsal).
Research on duration- duration of LTM
Harry Bahrick et al (1975) studied 392 American participants 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 yearbooks, (2) free recall test where participants recalled all the names of their graduating class.
Participants 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 accurate than recognition- about 60% after 15 years, dropping to 30% after 48 years. This shows LTM may last up to a lifetime for some material.
Strength-Baddeleys study-separate memory stores
One strength of Baddeleys study is that it identified a clear difference between two memory stores. Later research showed that there are some exceptions to Baddeleys findings. But the idea that STM uses mostly acoustic coding and LTM mostly semantic has stood the test of time. This was an important step in our understanding of the memory system, which led to the multi-store model.
Limitation-Baddeleys study-artificial stimuli
Used quite artificial stimuli rather than meaningful material. For example the word lists had no personal meaning to participants. So Baddeleys findings may not tell us much about everyday coding in different kinds of memory tasks, especially in everyday life. When processing more meaningful information, people may use semantic coding even for STM tasks. This suggests that the findings from this study have limited application.
Strength-Jacob’s study-valid study
It has been replicated. The study is very old and early research in psychology often lacked adequate controls. For example some participants digit spans might have been underestimated because they were distracted during testing (confounding variable). Despite this, Jacob’s findings have been confirmed by other, better controlled studies. This suggests that Jacob’s study is a valid test of digit span in STM.
Limitation-Millers research- not so many chunks
One limitation of Millers research is that he may have overestimated STM capacity. Nelson Cowan (2001) reviewed other research and concluded that the capacity of STM is only about 4 (plus or minus 1) chunks.
This suggests that the lower end of Millers estimate (five items) is more appropriate than seven items.
Limitations-Peterson and Peterson -meaningless stimuli in STM study
Stimulus material was artificially. The study is not completely irrelevant because we do sometimes try to remember fairly meaningless material (eg phone numbers). Even so, recalling consonant syllables doesn’t reflect most everyday memory activities where what we are trying to remember is meaningful. This means the study lacked external validity.
Strength-Bahrick et als study- high external validity
Reseachers investigated meaningful memories (ie of peoples names and faces). When studies of LTM were conducted with meaningless pictures to be remembered, recall rates were lower. This suggests that Bahrick et als findings reflect a more ‘real’ estimate of the duration of LTM.
