A person can just barely detect the difference between two weights: one weighs 12 pounds and the other weighs 10 pounds. What is the just noticeable difference for a weight of 70 pounds?

The concept of just noticeable difference (JND) is based on sensory perception and refers to the minimum amount by which a stimulus must be changed in order for the change to be noticeable. This idea is frequently described in relation to Weber's Law, which states that the JND is a constant proportion of the original stimulus.

In the context of the weights provided, the person can detect the difference between a 12-pound weight and a 10-pound weight, which is a difference of 2 pounds. To find the JND when the reference weight is increased to 70 pounds, the process involves calculating the proportional difference.

Using Weber's Law, the ratio of the difference (2 pounds) to the original weight (10 pounds) is 2/10 = 0.2 or 20%. Now, applying that same proportion to a 70-pound weight means that:

0.20 × 70 pounds = 14 pounds.

Therefore, the correct answer reflects that a person would need a difference of 14 pounds from 70 pounds to notice a change, which aligns with the principle of proportional difference outlined by Weber's Law. This method demonstrates how our perception of difference scales with the size of the initial stimulus.