What is memory?
Memory is a process of remembering information after the original thing is no longer present. There are 3 stages:
- Encoding (putting information in)
- Storage (maintaining and holding information)
- Retrieval (remembering and extracting information)
Capacity, duration, encoding
A measure of the amount of information that can be held in memory.
STM - 7 plus or minus 2. LTM - potentially unlimited.
A measure of how long a memory lasts before it is no longer available.
STM - 20 to 30 seconds. LTM - from hours to years.
The way information is changed so it can be stored in the memory. Information enters the brain via the senses and then is stored in various forms.
STM - acoustic or visual. LTM - semantic.
Types of memory
Sensory memory (SM)
A set of limited capacity, modality-specific stores that hold information very briefly.
Short-term memory (STM)
A temporary place for storing information, where it receives little processing.
Long-term memory (LTM)
A memory for events that have happened in the past. It has potentially unlimited duration and capacity.
Conrad (1964) - participants were shown sequences of 6 letters. They were asked to write them down as they appeared but the presentation was too fast to keep up with so info was held in STM. Errors made were acoustic confusion errors. It was concluded that encoding in STM is acoustic even when info is presnted visually.
Baddeley (1966) conducted one experiment to measure STM, and another to measure LTM. He used four word lists and found that errors made in recalling the words depended on the type of list and the time delay. STM - acoustic errors. LTM - semantic errors. This suggests that STM uses an acoustic code and LTM uses a semantic code.
Jacobs (1887) read lists of one syllable letters or numbers out loud, and increased length of list until participants could only recall 50%. STM capacity - 9 numbers/ 7 letters. STM increased with age - 8 year olds remembered 7 digits, 19 year old remembered 9.
Miller (1956) replicated Jacobs' findings, and came up with the phrase 'the magic number seven plus or minus two'.
There are no real studies on this - LTM capacity is potentially unlimited.
STM duration research
Peterson and Peterson (1959) - participants were read nonsense trigrams, then a 3-digit number to count backwards from in threes as a distractor task. After 3, 6, 9, 12, 15 or 18 seconds, participants had to recall the trigram. On average, they remembered 90% after 3 seconds, and 2% after 18 seconds. This suggests that the duration of STM is 20-30 seconds.
LTM duration research
Bahrick et al ( 1975) - 400 participants aged 17-74 years were asked to remember the names of classmates from high school (free recall task). They were also shown a set of photos and a list of names, some their ex school friends, and had to identify which were their ex school friends (recognition task). Those who'd left high school within 15 years recalled 90% of faces and names in recognition task. Those who'd left 48 years previously recalled 80% of names and 78% of faces. This suggests that LTM lasts a long time.