Capacity of STM - Jacobs (1887)

Question 1

Aim

Answer 1

To investigate the capacity of short-term memory (STM).

Question 2

Procedure

Answer 2

• Laboratory experiment
• Sample of 443 females aged between 8-19 years.
• Jacobs used the serial digit span technique:

1. Participants were presented with a series of digits or letters in a specific order.
2. They were then asked to recall the digits or letters in the same order immediately after presentation.
3. The length of the sequence started with three digits and increased by one digit each time until the participant could no longer correctly recall the sequence.

Question 3

Findings

Answer 3

• Average span of 5-9 items.

Question 4

Conclusion

Answer 4

• Capacity of STM is 7+/-2 chunks of information.
• Our STM stores chunks of information.

Question 5

Strength

Answer 5

• Laboratory experiment and therefore very controlled.
• Extraneous variables were controlled.
• For instance, an extraneous variable would have been the pace at which the letters/digits were read out. It would have been unfair if they were read quickly to some participants then slowly to others.
• To control this extraneous variable, a metronome was used to ensure they were all read at the same pace.
• Increases the reliability of the experiment.

Question 6

Weakness

Answer 6

• Lacks ecological validity due to artificial nature of the experiment.
• People don’t tend to recall strings of letters or numbers in everyday life (unless they are trying to remember a phone number, for example).

Question 7

Weakness

Answer 7

• Lacks population validity.
• Although a large sample of 443 females were used, their age range was very narrow (8-19 years).
• Therefore we cannot apply the findings of this experiment to other age categories, such as an older population.