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Memory and Forgetting
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Comprehensive and detailed notes covering the topic of memory.
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Chapter 2- Memory-TextbookSensory Register:
Temporarily stores information from our senses (sight, touch, taste, and smell)- it’s constantly receiving
information around us
Unless we pay attention to it, it disappears quickly through spontaneous decay-the trace just fades
The sensory register has a limited capacity, and a very limited duration (I.e. we can remember a little
information for a very short time)
Information is coded depending on the sense that has picked it up- e.g. visual, auditory or tactile.
Short-Term Memory:
Short-term memory has a limited capacity and a limited duration
Coding is usually acoustic
Long-Term Memory:
Essentially unlimited capacity and is theoretically permanent. Coding is usually semantic.
There are different types of LTM:
Episodic memory stores information about events that you’ve actually experienced, such as a concert or a
visit to a restaurant. It can contain information about time and place, emotions you felt, and the details of
what happened.
Semantic memory stores facts and knowledge that we have learnt and consciously recall, such as capital
cities and word meanings. It doesn’t contain details of the time or place where you learnt the information.
It’s simply knowledge.
Procedural memory stores the knowledge of how to do things, such as walking, swimming or playing the
piano. This information can’t be consciously recalled.
Iconic memory is the term used to describe visual material. Echoic is the term used to describe sound.
Sensory Register Short-Term Memory Long-Term Memory
Capacity Sensory experience 7 +/-2 unlimited
Duration ¼-½ a second 18-30 seconds A few years-lifetime
Coding Sense specific acoustically Imagery and semantically
,Coding, Capacity and Duration of Memory
Our everyday experience of memories is that there are two main types. Some are brief and quickly forgotten, but
others can last a very long time. Psychologists broadly agree and have investigated in great detail the features of
what they call short-term memory and long-term memory.
Key Terms:
Coding- The format in which information is stored in the various memory stores.
Capacity-The amount of information that can be held in a memory store.
Duration-The length of time information can be held in memory.
Research on coding:
Once information gets into the memory system, it is stored in different formats, depending on the memory store.
The process of converting information from one form to another is coding. Alan Baddeley (1966a&1966b) gave
different lists of words to four groups of participants to remember:
Group 1 (acoustically similar): words sounded similar (e.g. cat, cab, can).
Group 2 (acoustically dissimilar): words often sounded different (e.g. pit, few, cow).
Group 3 (semantically similar): words with similar meanings (e.g. great, large, big).
Group 4 (semantically dissimilar): words that all had different meanings (e.g. good, huge, hot).
Participants were shown the original words and asked to recall them in the correct order. When they had to do this
recall task immediately after hearing it (STM recall), they tended to do worse with acoustically similar words.
If participants were asked to recall the word list after a time interval of 20 minutes (LTM recall), they did worse with
semantically similar words. This suggests that information is coded semantically in the LTM.
Evaluation:
Artificial Stimuli-One limitation of Baddeley's study was that it used quite artificial stimuli rather than meaningful
material. The word list had no personal meaning to the participants. This means we should be cautious about
generalising the findings to different kinds of memory task. For example, 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.
Research on capacity:
Digit span:
How much information can STM hold at any one time, I.e. what is its capacity? Joseph Jacobs (1887) developed a
technique to measure digit span. The researcher gives, for example, 4 digits and then the participant is asked to
recall these in the correct order out loud. If this is correct the researcher reads out 5 digits and so on until the
participant cannot recall the order correctly. This determines the individuals 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 (1956) made observations of everyday practice. For example, he noticed that things come in sevens:
there are seven notes on a musical scale, seven days in a week, seven deadly sins and so on. This suggests that the
span (or capacity) of STM is about 7 items (plus or minus 2). However, Miller also noticed people can recall 5 words
as well as they can recall 5 letters. They do this by chunking-grouping sets of digits or even letters in units or chunks.
Evaluation:
Lacking validity-one limitation of Jacobs’ study is that it was conducted a long time ago. Early research in psychology
often lacked adequate control. For example, some participants may have been distracted while they were being
tested so they didn’t perform as well as they might have. This would mean results might not be valid do to these
confounding variables. However, the results of this study have been confirmed in other research confirming its
validity.
Not so many chunks-one limitations of Miller’s research is that he may have overestimated the capacity of STM. For
example, Cowan (2001) reviewed other research and concluded that the capacity of STM was only about four
chunks. This suggests that the lower end of Miller’s estimate (five items) is more appropriate than seven items.
, Research on duration
Duration of STM:
Duration is the defining feature of STM. Margaret and Lloyd Peterson (1959) 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 (also
known as a trigram, such as YCG) to remember and was also given a 3-digit number until told to stop. The student
was then asked to count backwards from that three-digit number until told to stop. This counting backwards was to
prevent any mental rehearsal of the consonant syllable (which would increase the student’s memory for 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. Their findings suggest that STM may have a very short duration unless
we repeat something over and over again (I.e. verbal rehearsal).
Evaluation
Criticising Peterson and Peterson-One explanation for why we forget things in STM is that the memory trace simply
disappears if not rehearsed (spontaneous decay). An alternative explanation is that the information in STM is
displaced-STM has a limited capacity and any new information will push out what is currently there. In the study by
Peterson and Peterson, participants counted down during the retention interval. Meaning information could be
replaced’.
Duration of LTM:
Harry Bahrick and colleagues (1975) 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 from their graduating class.
Participants who were tested within 15 years of graduation were about 90% accurate in photo recognition. After 48
years, recall declined 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 LTM can last a very long time.
Evaluation:
Meaningless stimuli in STM study-a limitation of Peterson and Peterson’s study is that the stimulus material was
artificial. Trying to memorise consonant syllables does not reflect most real-life memory activities where what we
are trying to remember is meaningful. So, we might say this study lacked external validity. However, we do
sometimes remember meaningless things such as phone numbers, so this study is not totally irrelevant.
Higher external validity-one strength of Bahrick et al’s study is that it has higher external validity. Real-life
meaningful memories were studied. When studies on LTM have been conducted with meaningless pictures to be
remembered, recall rates were lower (e.g. Shephard 1967). The downside of such real-life research is that
confounding variables are not controlled. Such as the fact that Bahrick’s participants may have looked at their
yearbook photos and rehearsed their memory over the years.
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