When a sound enters the ear it sets up a vibration pattern along the basilar membrane. This vibration pattern initiates nerve pulses which travel along the eighth nerve to the brain, where a second pattern of neural activity results. Two general methods may be used to study these patterms: (1) the objective measurement of cortical potentials by the electro‐physiologist, and (2) subjective measurements such as masking and fatigue effects. The present paper is based on the latter procedure in which the results of loudness and fatigue tests have been combined to give patterns of cortical activity in terms of millisones per kappa‐band. Use of fatigue patterns permits employment of a low level probe tone which overcomes the difficulties formerly experienced with artifacts in masking patterns due to beats and distortion products.