Weber's law relates to which concept?

• A. Difference threshold
• B. Detecting stimuli under uncertainty
• C. Focusing on one stimulus
• D. Light entering the eye

Answer: (A)

Weber's law describes how the smallest detectable difference between two stimuli relates to the original intensity. The key idea is that the just noticeable difference (the difference threshold) is a constant proportion of the initial stimulus, not a fixed amount. This is written as ΔI / I = k, where ΔI is the change in intensity, I is the starting intensity, and k is a constant for a given sense.

In practice, this means the amount you must change a stimulus by scales with how strong the stimulus is. For example, about a 2% change might be noticeable for weight, so a 100-gram object needs roughly a 2-gram difference, while a 1,000-gram object needs about a 20-gram difference. The other options point to different ideas: detecting stimuli under uncertainty relates to signal detection theory, focusing on one stimulus touches on selective attention, and light entering the eye concerns optical entry and initial transduction—not the proportional change Weber's law describes.