Sound-level coding in the auditory nerve is achieved through the progressive recruitment of auditory nerve fibers (ANFs) that differ in threshold of activation and in the stimulus level at which the spike rate saturates. To investigate the functional state of the ANFs, the electrophysiological tests routinely used in clinics only capture the first action potentials firing in synchrony at the onset of the acoustic stimulation. Assessment of other properties ( e.g . spontaneous rate and adaptation time constants) requires single-fiber recordings directly from the nerve, which for ethical reasons is not allowed in humans. By combining neuronal activity measurements at the round window and signal-processing algorithms, we constructed a peri-stimulus time response (PSTR), with a waveform similar to the peri-stimulus time histograms (PSTHs) derived from single-fiber recordings in young adult female gerbils. Simultaneous recordings of round-window PSTR and single-fiber PSTH provided models to predict the adaptati...