Answer:
b. difference threshold
Step-by-step explanation:
In psychology, the difference threshold, also known as just noticeable difference, refers to the slightest difference between two stimulations that an individual is able to detect. These stimuli could be, for example, a small difference in the weight or size of two objects, a slight difference in sounds, etc.
In this case, a person is asked to listen to a series of tones presented in pairs, and asked to say whether the tones in each pair are the same or different in pitch. Therefore, the researcher is most likely measuring the individual's difference threshold.