BCS 111 Unit 6.2

An overview of our memory system

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Testing processing and short-term storage capacity

• Free-recall experiment

  • Listen carefully. Memorize as many words as you can

Testing processing and short-term storage capacity

• What factors may affect your recall?

• What are some possible confounding variables?

• Did you use any kind of strategy to help you recall?

Testing processing and short-term storage capacity

What factors may affect your recall (possible confounds)?

• To name just a few:

  • Length of the list

  • Whether you can see the actual object

  • Speed of presentation

  • Word length

  • Concreteness of words

  • Word frequency

Testing processing and short-term storage capacity

• Serial position effect: the first few words (Primacy effect) and the last few words (Recency effect) on the list are typically recalled better.

Serial position effect: Primacy vs. Recency effect

• How do we disrupt primacy effect?

• How do we disrupt recency effect?

Effect of presentation speed

• Fast presentation yielded a weaker primacy effect than slow

• No diff. in recency effect between fast and slow

Short term memory

• Capacity

  • Magic Seven (plus or minus two)

  • One strategy for improving storage capacity: chunking

• How would you remember the following letter string?

• M L B O N C B S N N F L O N E S P N

  • top-down process

Short term memory: retention

• The longer you count (i.e., recall interval), the poorer the recall performance

  • Probability of recall as a function of recall interval

  • Encoded info decays in about 20 s

Short term memory - retrieval

In terms of order:

• Serial search: one-by-one search by order

• Parallel search: scan from multiple rows/columns; not by order

In terms of when to stop search:

• Self-terminating search: search stops when target detected

• Exhaustive search: scan through the entire display even if target already found

How do we scientifically test forgetting in short term memory?

• Two competing hypotheses: Decay vs. Interference

• Probe digit task (Waugh & Norman 1965)

• 16-digit number

• Fast vs. Slow presentation → to test “decay” theory

• The number of interfering items (ranging from 1 to 12) → to test “interference” theory

Short term memory: Forgetting

• Two competing theories: Decay vs. Interference

  • Probe digit task (Waugh & Norman 1965)

  • Hypotheses:

  • 1. If poorer recall in slow presentation than fast → the claim of decay is valid.

  • 2. If no diff between slow and fast, then interference is valid

Two competing theories: Decay vs. Interference

Hypotheses:
1. If poorer recall in slow presentation than fast → the claim of decay is valid.
2. If no diff between slow and fast, then interference is valid