Sensory stores

The sensory store cannot hold pieces of information for very long. It encounters rapid forgetting through decay. It is an iconic store. Iconic memory is the visual sensory memory register pertaining to the visual domain, and a fast-decaying store of visual information. Iconic memory is very brief (<1000ms).

Sperling (1960) used the partial report paradigm to investigate iconic stores. Observers were shown a 3x3 or 3x4 array of letters. Recall was based on a cue which followed the offset of the stimulus and directed the subject to recall a specific line of letters from the initial display.

Whole report condition required participants to recall as many letters in their proper spatial locations as possible. Participants were typically able to recall 3-5 characters from the 12 character display. This suggests whole report is limited by a memory system with a capacity of 4-5 items.

Partial report condition required participants to identify a subset of characters using cued recall. The cue was a tone which sounded at various time intervals. The frequency of tone indicated which set of characters were to be reported. Partial report results showed participants could recall most letters (9 out of 12) in a given row, suggesting that 75% of the entire visual display was accessible to memory.

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Short-term memory

Forgetting in the short-term memory store occurs through displacement and decay. STM has a very limited capacity (about 7 units). Storage is very fragile - distraction and lack of rehearsal can lead to information loss. Peterson & Peterson found that over 18 seconds, items in the short-term memory store experienced rapid decay. At 3 seconds, participants could recall around 95% of letters. At 18 seconds, participants could recall around 5% of letters.

Trace decay theory: forgetting occurs as a result of the automatic decay/fading of the memory trace. Information can be held for around 15-30 seconds before it begins to decay.

Displacement theory: when STM is 'full' (over 7 or 9 items), new information displaces old information and takes its place. The old information which is displaced is forgotten.

Interference theory: memory can be disrupted or interfered with by what we've previously learned or by what we'll learn in the future. Proactive interference = when you can't learn a new task because of an old task. Retroactive interference = when you forget a previously learnt task due to the learning of a new task

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Long-term memory

Forgetting in the long-term memory store occurs through retrieval failure.

Retrieval failure theory: the information is in the LTM store but can't be accessed. It is still available/stored but it just can't be retrieved. It has been suggested that this failure of retrieval may occur because the retrieval cues are no longer present. Encoding specificity principle is also relevant here.

Cue-dependent forgetting (Tulving, 1974): retrieval cues may be based on context - the setting or situation in which the information was encoded in. Godden & Baddeley's diver study demonstrates the use of cues and the forgetting which occurs when they aren't present. Divers who had to memorise a word list had better recall when the same condition (i.e dry land or underwater) was reinstated during recall. Tulving & Pearlstone (1966) asked participants to learn word lists of words belonging to different categories. When recalling the words, those who were given the category names recalled substantially more. The categories provided context, and naming the categories provided retrieval cues.

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Active forgetting

Memory suppression

  • Freud: repression is pushing unwanted memories out of consciousness, forcing them into the unconsciousness.
  • Active suppression of information leads to worse memory (Anderson, 2004)
  • Controlling unwanted memories by way of suppression was associated with increased dorsolateral prefrontal activation, reduced hippocampal activation, and impaired retention of those memories (Anderson, 2004)

Infantile amneisa (for the first 3 years of life)

  • Psychodynamic explanations: repression of threat-related memories
  • Physiological explanations: hippocampus matures. Neurogenesis occurs.
  • Cognitive explanations: development of self-schema to organise memories. Context dependent memory.
  • Autobiographical memory peaks between ages 15-25
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