2.1.6

Capacity Studies

Test yourself

Sperling (1960)

Several experiments were conducted to measure the amount of information that was available to a person after brief exposures to visual stimuli; a.k.a. recall of the sensory register.

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Method

  • Participants were shown grids of letters: three rows of four letters.
  • Sperling chose letters as they have a large amount of information and they have been used by previous investigators.
  • Control tests were done first to measure the individual’s ability to recall the letters as this will be unique.
  • Essentially, these were meant to establish a baseline for the individual.
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Method cont.

  • The experiment showed the participants a grid of letters (three rows of four letters) for 0.05 seconds (50 milliseconds).
  • There were two different scenarios:
    • Recall the whole grid.
    • Recall a single row.
  • The row to be recalled was identified by a high/medium/low tone that was played directly after the grid was flashed.
  • The participants did not know which row was to be selected.
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Results

  • First scenario - recall the whole grid:
    • Participants only managed to recall four or five letters out of a total of 12 letters.
  • Second scenario - recall a single row:
    • They could only recall three letters (out of four letters in one row).
  • These results were consistent no matter which row was selected.
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Conclusions

  • First of all, the sensory register is finite. Humans can only process and recall a small amount of sensory information.
  • Secondly, as the participants did not know which row was to be selected, they viewed the whole grid. This means the entire grid was in their sensory register.
  • But they could not recall all of the letters as the trace faded and the information decayed.
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Evaluation

  • This was a highly controlled laboratory experiment, so it was scientific and it is easy to replicate.
    • This means that the results are more reliable.
  • But laboratory experiments such as this do not reflect real-life scenarios (you are hardly ever expected to recall a grid of letters).
    • So the study had low ecological validity.

Jacobs (1887) - Capacity of Short Term Memory

Capacity is the measure of how much information can be stored in memory. Jacobs studied the capacity of short-term memory (STM) and found that STM had a limited capacity.

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Method

  • This was a laboratory experiment.
  • Participants were asked to recall a sequence of either letters or digits.
  • They had to recall them in the order in which the sequence was presented.
  • They repeated this procedure until they could not recall the sequence accurately.
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Letter and digit sequence example

  • Letter sequence example:
    • A, AO, AOP, AOPH, AOPHQ, AOPHQR, … etc.
  • Digit sequence example:
    • 9, 98, 984, 9845, 98452, 984523, 9845230, 98452309… etc.
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Results

  • Generally, participants could recall a longer string of digits than of letters.
  • On average, they could recall nine digits and seven letters.
  • The capacity of short-term memory increased with age.

Jacobs (1887) - Conclusions

Capacity is the measure of how much information can be stored in memory. Jacobs studied the capacity of short-term memory (STM) and found that STM had a limited capacity.

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Capacity

  • Jacobs concluded that the capacity of short term memory is finite.
  • There is a limit on how much information can be stored, and so recalled, accurately within short-term memory.
  • Jacobs established the capacity to be between five to nine pieces of information.
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Influence of age

  • The capacity may increase with age because of learning or memory techniques.
    • E.g. chunking the information:
  • The digit sequence “98452309” could be chunked into two sets of numbers “9845” and “2309”.
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Digits vs letters

  • Finally, Jacobs concluded that the digits may have been easier to recall because there are only 10 possible digits compared to 26 possible letters.
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Extraneous variables

  • A strength of this study is the control of extraneous variables because it was a laboratory experiment.
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Ecological validity

  • But because it was a laboratory experiment, it was artificial and lacked ecological validity.
  • Strings of random digits and letters are not very meaningful, so are less likely to be recalled.
  • A test on meaningful information, such as actual words or phone numbers, may show that STM capacity is actually larger than concluded in this study.
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Methodological issues

  • A final weakness could be the confusion that could result from similar sequences between current and previous trials.
  • If presented with similar sequences, participants could muddle them up, confounding the results.

Jump to other topics

1Social Influence

2Memory

3Attachment

4Psychopathology

5Approaches in Psychology

6Biopsychology

7Research Methods

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17Option 3: Addiction (A2 only)

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