Capacity, Duration & Encoding

• Miller did not specify the size of each 'chunk', so the exact capacity of short-term memory is still unknown.
• Other factors, such as age, may also affect short-term memory capacity.
• In Peterson & Peterson the use of Psychology students may introduce demand characteristics and decrease validity.
• In Peterson & Peterson the lack of ecological validity raises questions about its applicability to everyday memory situations.
• In Peterson & Peterson there were high levels of control and replicability, which contribute to its reliability.
• In Peterson & Peterson using students in the sample limits generalisation.
• Peterson & Peterson has low population validity as the sample do not represent the wider population.
• Bahrick’s research used a sample of 392 American university graduates and therefore lacks population validity.
• Bahrick's research is culturally biased (ethnocentric), so limits generalisation.
• Bahrick's study only used students so has poor generalisation.
• Bahrick’s study has high levels of ecological validity as the study used real life memories.
• Wagenaar (1986) kept a diary over the course of six years which recorded over 2,400 events. He tested himself on the events and found a 75% recall after 1 year and a 45% recall after 5 years, suggesting that the capacity of the long term memory is very large, potentially limitless.
• The capacity of STM can be significantly altered by factors such as age (reduces) and practice (increases).
• Cowan (2001) concluded that the capacity of STM is 4 +/-1 chunks suggesting Miller's lower limit is more accurate.
• Many of the supporting studies are lab experiments so lack ecological validity.
• Many of the tasks on capacity and duration do not reflect real life so lack mundane realism.
• Many of the memory experiments can be replicated easily so have high reliability.