Answer: Absolute threshold
Explanation: The absolute threshold is the minimum amount of energy, or quantity of a stimulus, required for it to be reliably detected at least 50% of the time it is presented. In this example, thedoctor is trying to find the quietest sound Ann can reliably detect (i.e., the absolute threshold). In contrast, to determine a difference threshold, the doctor would need to ask Ann if she perceived two sounds as being the same or different volumes.