Perceived change in stimulus intensity is proportional to the logarithm of actual change.
Weber's 1834 finding, refined by Stevens's power law. It is why price differences matter proportionally rather than absolutely, and why a saving worth crossing town for on a small purchase is ignored on a large one.
In practice
- A shopper who drives to a second supermarket to save 30p on milk buys the sofa without asking whether the price moves.
- A room lit by two candles looks markedly brighter than one lit by a single candle; adding two candles to a hundred is not visible.
- Standing
- Refined by Stevens's power law.
- Further reading
- Wikipedia
- Subject
- Psychology & Behavior
- Essay
- A century and a half of measuring the mind