Which law states that the just noticeable difference is proportional to the baseline level of the stimulus?

• A. Fechner's Law
• B. Weber's Law
• C. Signal Detection Theory
• D. Stevens' Power Law

Answer: (B)

This question focuses on how our senses detect changes in stimulus intensity. The just noticeable difference (the smallest detectable change) scales with the baseline level of the stimulus, meaning the ratio ΔI/I is constant. This is Weber's Law: ΔI / I = k, where ΔI is the JND, I is the baseline intensity, and k is a constant.

Think about it with an example: if the baseline is 100 units and k is 0.02, the JND is 2 units. If the baseline increases to 200 units, the JND rises to 4 units. The proportional change needed to notice a difference stays the same even as the baseline grows.

This differs from Fechner's Law, which links perceived intensity to the logarithm of stimulus intensity rather than the change threshold; and from Signal Detection Theory, which deals with distinguishing signal from noise under uncertainty rather than how thresholds scale with baseline. Stevens' Power Law describes how perceived magnitude grows with stimulus intensity using a power function, not a fixed proportion for detection thresholds.

So, the statement about the JND being proportional to the baseline aligns with Weber's Law.