Fourteen people with normal hearing participated in a study that used signal detection theory to examine central auditory masking. Participants were tested in a sound-attenuating chamber. Absolute thresholds for stimuli (1000 Hz pure-tone, white noise masker at 40 dB SL) were established: first for the tone, then for the tone in combination with the masker in the contralateral ear. A mean threshold increase (3.8 dB) demonstrated central masking. Contrary to prediction, a paired-samples t-test revealed significant shifts in participant sensitivity (d´) [t (10) = 4.46, p < .001], suggesting that participants’ sensitivity to the tone decreased in the masking condition. These findings provide support for the theory that central masking is an auditory processing phenomenon.