A representation of the pure−tone loudness function given by Ψ = xϑF (x), where x is the ratio of stimulus to threshold intensity, is discussed. The form of F (x) is obtained from the empirical loudness curves at 1000 and 250 Hz. The structure of F (x) is shown to be in quantitative agreement with known steady−state driven firing rate activity of eighth−nerve units. We suggest that F (x) is proportional to the driven firing rate function RD(x) of the auditory sensory receptor. A specific choice is made for the algebraic form of RD(x) by identifying it with the driven rate function in a sensory receptor model proposed recently by Zwislocki. Within the model, a three−parameter fit to the loudness function is obtained. It is shown that similar results can be obtained for vibrotaction.Subject Classification: 65.35, 65.50.