Theory of TTS

Abstract

Laws stating that TTS varies as the logarithm of time disagree with experimental results very early or very late in these processes. Better agreement with observations results from regarding TTS as the sum of four components that vary exponentially with time. During constant stimulation, each component increases, approaching an upper limit asymptotically. After stimulation is terminated, each component diminishes toward zero asymptotically. Using data from published TTS studies, the magnitude and time constant of each component was determined. One component grows toward a limiting value dependent on stimulation intensity and test frequency, gaining half the remaining magnitude every 45 min; and decays afterward so that the magnitude is halved every 3 h. Another component grows to about 13 dB in most exposures and, afterward, decays to half-value every 8 min. Two more components, one positive and the other negative, decay at rapid but different rates to produce the “bounce” often observed during the first 2 min of recovery. Only the first-mentioned component seems related to permanent noise-induced hearing loss. The simple electrical analog of the theory makes possible a simple TTS meter for appraising noise hazard.