Final answer:
The just noticeable difference (JND), also known as the difference threshold, is the smallest detectable difference between two stimuli. It can vary depending on the specific weights being compared. The JND is not proportional to the overall magnitude of the stimulus, but is a constant fraction of the original stimulus.
Step-by-step explanation:
The just noticeable difference (JND), also known as the difference threshold, is the smallest detectable difference between two stimuli. It refers to the minimum amount of change in a stimulus that can be detected by a person 50% of the time. In the case of weight, the JND between a one-pound bag of rice and a larger bag would vary depending on the specific weights being compared. For example, if the JND is 0.1 pounds, a one-pound bag would feel the same as a 1.1-pound bag, but less than a 1.2-pound bag.
When comparing a 20-pound bag to a larger bag, the JND would still be determined by the specific weights being compared. If the JND is 4 pounds, a 20-pound bag would feel the same as a 24-pound bag, but less than a 28-pound bag. Thus, the JND is not proportional to the overall magnitude of the stimulus, but rather a constant fraction of the original stimulus, as specified by Weber's Law.