Coding of Amplitude-Modulated Tones in the Midbrain Auditory Region of the Frog

Until recently it was generally accepted that the ability to reproduce temporal aspects of sounds deteriorated from the peripheral to central regions of the auditory pathway. This conclusion was made from experiments using gated tones and noises and from others dealing with sound waveform reproduction. But the investigation of response modulations produced by small amplitude modulations of sounds have shown that the situation is far more complicated. In auditory nerve fibers the frequency domain response functions for modulation are lowpass functions having cutoff frequencies in the range of 1000 Hz. Amplitude-modulated sounds with small amplitude modulation give rise to a modulation of a discharge rate in only a narrow range of sound intensities (Moller, 1981).