Masking‐period patterns produced by very‐low‐frequency maskers and their possible relation to basilar‐membrane displacement

By using masking‐period patterns (MPP), produced by sinusoidal as well as impulsive maskers with very‐low‐frequency components, it could be demonstrated for man that the basilar membrane seems to move in phase for low sinusoids and preserves the waveform for nonsinusoids with low‐frequency spectrum within the two basal turns of the cochlea. The shape of a MPP is strongly correlated to the second derivative of the time function of the sound pressure at the eardrum for frequencies below 40 Hz, but to the first derivative for frequencies above 40 Hz. This is presumably due to the form of the cross section of the cochlea and the size of the helicotrema in man. Data of many MPP are shown and discussed together with patterns given in former papers on a qualitative and a quantitative level, leading to the following proposal: the higher peak in MPP belongs to a kind of suppression which would correspond to the displacement of the basilar membrane towards scala tympani, while the lower peak in MPP belongs to the excitation which would correspond to the displacement of the basilar membrane towards scala vestibuli.