John D. Durrant

Cochlear Inner and Outer Hair Cells: Functional Differences

The cochlear microphonic response was measured with differential electrodes from the first and third cochlear turns of normal guinea pigs and those treated with the ototoxic drug kanamycin. Histological controls showed that the outer hair cells in treated animals were missing over the basal half of the damaged cochleas, while the inner hair cells were intact. Measurements are consistent with the hypothesis that the potentials produced by inner hair cells are proportional to the velocity of the basilar membrane, whereas potentials generated by outer hair cells (which dominate the response of normal cochleas) are proportional displacement of the basilar membrane.

Modification of DIF summating potential components by stimulus biasing

Positive and negative components of the summating potential (DIF SP) recorded with differential electrodes were studied in the presence of a low‐frequency stimulus at different phases of this bias signal. Two clearly discernible ranges of behavior were observed depending on the sound‐pressure level of the low‐frequency stimulus. At the lower stimulus biasing levels, the SP components could be reversibly enhanced or depressed according to the magnitude (or equivalent magnitude at different phases) of the bias. At the higher intensity ranges, the SP output was generally depressed. The latter effect on the SP is a manifestation of the interference phenomenon.

On the Derivative Relationship between Stapes Movement and Cochlear Microphonic

It is demonstrated that the cochlear microphonic (CM response recorded from both first and third turns of the guinea pigs cochlea) is a square wave in time in response to triangular motion of the malleus. The results support the hypothesis that CM is proportional to stapes velocity.

Influence of Direct‐Current Polarization of the Cochlear Partition on the Summating Potentials

The effects of electrically biasing the cochlear partition on the summating potentials were investigated in guinea pigs. The DIF (DIF = SV − ST) and AVE (2 AVE = SV + ST) SP responses were observed under polarization as well as the cochlear microphonics. These responses were recorded and the cochlear partition was polarized in the first and third turns; a wide range of stimulus parameters was utilized. The negative DIF and positive AVE components exhibited similar qualitative effects of electrical biasing as the (pure tone) CM, but the amount of change induced in the former responses was typically three or more times greater than that seen in the CM. While the DIF+ exhibited the opposite effects of polarization, compared to these responses, the results revealed an underlying relationship between the positive and negative DIF responses. As a rule, positive polarization currents caused the DIF responses to become less positive and more negative while the opposite was true for negative currents. No systemati...

Effects of differing states of attention on acoustic reflex activity and temporary threshold shift.

Temporary threshold shift (TTS) and acoustic reflex activity were observed in 20 normal hearing subjects under several different states of attention. The Zwislocki acoustic bridge (model 3) was used to monitor acoustic reflex activity. Compliance shifts (changes in relative compliance) were measured during exposure of the contralateral ear to a 1000 Hz narrow‐band noise presented at 105 dB SPL, and TTS was measured at 1000 Hz for the contralateral ear after approximately 412 min of noise exposure. These measures were taken under three different conditions or modes of attention as defined by task performance: reverie (no task performance, high auditory attention), intelligibility test, and high visual attention (visual‐motor task). Also, levels of attention, as operationally defined by levels of task performance, were considered. From the results of this and other investigations it was concluded that there is a so‐called central factor involved in acoustic reflex activity although task performance per se, ...

Comparison of Effects of Biasing the Cochlear Partition with Electrical Current and Sound Stimulation on the DIF SP Responses

Summating potential responses were measured utilizing the differential recording technique. Two experimental designs were incorporated, one in which the cochlear partition was electrically biased with direct current and the other in which the movement of the partition was “biased” with a low‐frequency sound stimulus. The DIF− and DIF+ components were of prime interest. It was found that dc polarization and the mechanical bias have strikingly similar effects on the SP under certain conditions. The SP can be reversibly augmented or depressed according to the direction of current flow or direction of the biasing displacement, and, furthermore, the two DIF components exhibit change in the same absolute direction. A decrease in the DIF− and an increase in the DIF+, and vice versa, is produced by a given biasing stimulus. It is surmised that the net biasing effect is such that when the scala media potential is caused to increase (directly by current or indirectly by deformation of the cochlear partition), the D...

The Effects of dc Current Polarization on Cochlear Harmonics

The effects of dc polarization of the cochlear partition were observed on harmonic distortion components in microphonics. The qualitative effects of negative polarization (scala vestibuli negative) were quite consistent and similar to those observed in the polarization of intermodulation distortion components. The effects of positive polarization were much more variable, but the general trends of the data suggest that when the stimulus is presented below 85–95 dB SPL, the harmonic distortion output is enhanced by both positive and negative polarizing currents. At higher intensities, these components behave much as the fundamental microphonic component. These results have been interpreted as indications that electromechanical and hydromechanical nonlinearities, respectively, dominate the distortion process over low‐ and high‐intensity ranges.

Comments on the effects of overstimulation on microphonic sensitivity

Utilizing the differential recording technique, microphonic isopotential measurements were carried out before and after overstimulation. Recordings were made in the first and third turns of guinea pig cochleas. The exposure stimuli were pure tones of frequencies near the best frequency of the recording site. The results were suggestive of differences in the effects of overstimulation in different turns of the cochlea, at least as they are manifested electrophysiologically.

Comparison of remote extracochlear versus intracochlear recordings in guinea pig

Current techniques in human electrocochleography often rely upon recordings at sites quite remote from the origins of the recorded responses. There is presently little detailed information concerning the extent to which the appearance of the cochlear electrical responses are altered by volume conduction to remote sites such as the ear canal. A comparative study was made of the whole‐nerve action potential (AP) recorded from a wire electrode placed on the eardrum (TM) in the guinea pig [analogous to the technique used in humans by Cullen et al., Acta‐Otolaryngal. 74, 15–22 (1972)] and an intracochlear electrode placed in scala tympani of the first turn (ST1). For purposes of comparison, an additional electrode was often placed in scala tympani of the third turn (ST3). Cochlear microphonics (CM) and summating potentials (SP) were also studied. It was consistently observed that in the TM recording the N2 of the AP is proportionally larger in relation to the N1 magnitude than in the ST1 recording. However, N2...

Effect of Relevant Cues on Attention in Binaural Listening

Several experimenters have demonstrated the importance of the relevance of information in complex listening situations. However, in general, these experimenters have concerned themselves mainly with the decremental effects of irrelevant information on task performance and attention selection of one of two competing messages. The present writer is concerned with the influence of relevant information, i.e., the effects of inserting relevant cues into irrelevant information presented at the nontest ear. Twenty‐three college students (experimental group) were given an intelligibility test under this condition—i.e., word lists presented at one ear and irrelevant contextual speech, with inserted cues, at the other ear. Twenty‐nine college students received the same test under the same condition, but without the cues. The attention selection of the cues significantly improved the scores of the experimental group over those of the control group. Various operant factors in the test situations with their “real life...