Keegan notices that his favorite 55-cent candy bar seems lighter than usual and so he checks the label to find that it is lighter by ½ ounce. He decides to buy a larger candy bar instead and doesn't notice that the 99-cent candy bar is also ½ ounce lighte

Keegan's behavior illustrates the fact that:
A) the just noticeable difference is not a reliable measure of psychophysiological judgment.
B) sensory adaptation may occur in the short time between holding one candy bar and then the other.
C) difference thresholds are unpredictable because sometimes he can and sometimes he can't detect a ½ ounce change.
D) the larger a weight is, the greater the change must be before one can detect a difference.

Answer: D
Rationale: A difference threshold is the smallest detectable difference between two stimuli. Whether you detect a difference, known as a just noticeable difference, depends on the intensity of the original stimulus. The more intense the original stimulus is, the more of it that must be added in order for the difference threshold to be reached. In this example, Keegan was able to notice the ½ ounce difference in the 55-cent bar because the original bar was relatively light. Because the 99-cent bar was heavier to begin with however, Keegan was not able to detect a change in weight of only ½ ounce.