When Ann went to her doctor, he gave her a hearing test. During the test, the doctor presented tones to Ann through earphones. The tones varied only along the loud-soft dimensions (from very loud to very soft). The doctor asked Ann to raise her hand whenever she heard a sound. The doctor was testing Ann's ________.
◦ absolute threshold
◦ subliminal perception
◦ auditory convergence
◦ refractory threshold
◦ difference threshold