Cognitive Psychology: The Mind's Clever Shortcuts
A tour of how we perceive, attend, remember, reason and decide, and of the surprising ways the mind cuts corners.
Try 3 questions
1. You can just notice 1 extra gram on a 50-gram letter. By Weber's law, how much must you add to a 500-gram package to notice?
- About 10 grams
- About 1 gram
- About 100 grams
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Answer: About 10 grams
Weber's law says the just-noticeable difference is a constant fraction of the original: 1/50 is 2%, and 2% of 500 grams is 10 grams.
2. Even with one eye closed, you don't see a hole where your blind spot is. Why not?
- Constant eye movements erase the gap completely
- The brain fills the gap from surrounding input
- The blind spot only appears in dim light
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Answer: The brain fills the gap from surrounding input
Where the optic nerve leaves the eye there are no receptors, but the visual system interpolates from the surrounding pattern, so you perceive a seamless scene.
3. The same ambiguous symbol is read as 'H' in 'THE' and as 'A' in 'CAT'. What does this demonstrate?
- Bottom-up processing of raw visual features
- Top-down processing: context shapes perception
- Sensory adaptation to repeated letter shapes
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Answer: Top-down processing: context shapes perception
Your knowledge of words feeds back into perception, so identical input is seen differently depending on the surrounding letters.
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