Intracochlear electrodes in the guinea pig are used to measure the relations among cochlear potentials in response to slow acoustic transients. The traveling wave of B•k•sy is described in terms of cochlearmicrophonic (CM) voltage as functions of time and place along the cochlear partition. The results are consistent with previous observations in the ear and on models of the basilar membrane. Interpolations of wave velocity and wave amplitudes between places used for the measurements allow continuous representations of the traveling-wave pattern of CM in either sI•ace or time. From these representations, it is clear that the duration of the stimulating phase of CM along the cochlear partition significantly exceeds the apparent duration of the whole-nerve action-potential (AP) response to these transients.Selective changes in the waveforms of the AP responses, as opposed to simple reductions in amplitude, are observed when the transients are accompanied by bands of noise and after local chemical or mechanical injury to the organ of Corti. The selective changes in waveform allow consideration of the waveform removed from the normal AP response by the noise as well as the response remaining during noise. The responses removed by each of successive increases in the bandwidth of the noise reveal the presence of AP responses at times not apparent in the normal whole-nerve AP waveform. These observations are most easily explained by assuming that the basic neural response is diphasic as conventionally recorded. When neurons become active in an orderly sequence, the positive phases of the earlier individual responses coincide with and may conceal the negative phases of later responses. The whole-nerve AP waveform is thus considered as the convolution (complex product) of two functions in time, the diphasic unit of response and the numerical sequence of newly active neurons. An empirical model for the diphasic unit of response "divided" into the AP waveform reveals patterns of neural activity that are compatible with the traveling wave of CM. The same model satisfactorily explains several details of the whole-nerve AP waveform recorded during stimulation with a burst of high-frequency tone.

The ac ("microphonic") cochlear potential and the positive dc "endolymphatic" potential have been recorded simultaneously as the exploring electrode was introduced into scala media or as other parameters were varied. Negative intracellular dc potentials were demonstrated in the cells of the organ of Corti. The zone of positive endolymphatic potential is bounded by the reticular lamina, not by the basilar membrane. The cochlear microphonic reverses phase as the exploring electrode penetrates the reticular lamina. A dc polarizing current with the positive pole in scala media (and negative in scala tympani) increases the cochlear microphonic just as it does when the positive pole is located in the scala vestibuli. These facts indicate that the source of the ac (microphonic) potential seems clearly to be at the hair-bearing end of the hair cells and that the source of the dc endolymphatic potential is probably here also, while Reissner's membrane is not the source of either the ac or the dc potential. No steady dc current flow outside scala media was found such as would be expected if stria vascularis were the dc source and if the hair cells modulated a dc current flow through them. The dc endolymphatic potential may be increased by as much as 10 percent if and while the basilar membrane is displaced toward scala vestibuli and may be decreased to 50 percent or less when and while it is displaced toward scala tympani. Isotonic solutions rich in potassium depressed the ac potential and nerve responses when introduced into scala tympani but not when in scala vestibuli only. The dc potential, however, was not altered by high potassium concentration in scala tympani.

Frequencies of tones are mapped on to distances along the organ of Corti by associating behaviorally measured threshold shifts with regions of hair-cell loss. The central tendency found for 95 frequency-position matches by four observers on 21 ears is approximated by a straight-line, log-linear relation between frequency and position. Only a small portion of the considerable variation of individual matches around this function could be explained by length of the organ of Corti. Other unidentified factors appear to be responsible for most of these variations.

When the ear is stimulated by a steady tone scala media and scala vestibuli become less positive electrically relative to scala tympani. This ‘summating potential’ (SP) is a d.c. change related to the root-mean-square of the acoustic pressure, integrated over one or two waves. It increases up to injurious sound pressure levels. It is increased by additional positive polarization of scala vestibuli or media. It is modified and may even be reversed in sign by hydrostatic displacement of the cochlear partition. It broadly resembles the cochlear microphonic (CM) but is more resistant to most drugs and anoxia. The negative SP depends on the integrity of the internal hair cells. The external hair cells produce CM and may also generate small SPs, usually positive in sign. The SP generated by 7000 cps tone bursts is strong in the basal turn while those by 2000 and 500 cps are very small here but are strong in the second and third turns, respectively. The theory is proposed that the negative SP is the response of the internal hair cells, an amplifier action intermediate between a mechanical detector action of the cochlear partition and the excitation of nerve impulses. Both CM and SP depend on bending of the ‘hairs’ of the sensory cells in the proper direction.

In an effort to clarify certain ideas about the nonlinear behavior of the cochlea, a simple nonlinear network was studied. The network was constructed to produce peak-clipping distortion similar to that seen in the cochlear microphonic (CM) of the basal turn of the cochlea. The interference between pairs of tones and the growth of combination tones as well as other manifestations of nonlinearity were similar for the ear and for the network. The degree of similarity between the output of the network and CM from the ear is shown by instantaneous waveforms and by input-output functions. An important finding of this paper is that the linearization effect of two-tone interference in the ear is a property of nonlinear systems, which occurs in the network also. The results also support recent theories that summating potential (SP) is produced by asymmetric nonlinearities in the ear.