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It is commonly thought that the AP is determined by high frequency units in the most basal part of the cochlea, and that the frequency specificity of this response is rather poor. We have evaluated these relations for the 7 msec far field activity by means of masking experiments and recordings from the Vertex. Stimuli were tone bursts at 1, 2 and 4 kHz with rise-fall times from 1 to 3 msec. Peak duration 0.5 msec. Maskers were noisebands with center frequencies spaced at narrow intervals from 0.5 to 6 kHz. In all situations where the frequency for the masker and the stimulus were close to each other there were pronounced and characteristic changes in the response. The results clearly demonstrate that the 7 msec response reflects activity in the cochlea that is characteristic for each stimulus frequency. We were unable to detect any particular influence from the most basal part of the cochlea. There is thus a distinct discrepancy between the frequency selectivity for the AP and for the brainstem responses....

Mice of C57BL 6J strain were acoustically primed at 16 days of age and tested for audiogenic seizures 5 days later. Priming and testing stimuli consisted of 60 sec exposure to one of several pure tones at an intensity of 110 db. Priming at 5 and 7.5 kHz was found to be ineffective. In general, priming increased in effectiveness as a direct function of frequency. The same trend was evident for testing with higher frequencies resulting in more severe audiogenic seizures. In addition, some evidence was presented for both frequency specificity and generalization of acoustic priming.

The topographic arrangement and frequency sensitivity of units were studied in the inferior colliculus of urethane anaesthetized rabbits. Units in the central nucleus of the inferior colliculus were organized tonotopically, with neurones of low best frequency located dorsally and high best frequency ventrally in this structure. Units in the external nucleus of the inferior colliculus tended to be broadly tuned but the frequently observed habituative behaviour of these units often made the determination of tuning curves difficult in this region. In the central nucleus, tuning curves of low frequency elements were broader than those of high frequency units. Auditory activity was also observed in a small sample of units in the intermediate and deep layers of the superior colliculus. These results were discussed in relation to the neuronal architecture of the inferior colliculus and to the diversity of the sources of afferent endings in this structure. Units in the external nucleus would appear to have a different role to those in the central nucleus in the neural processes of hearing.

Two experiments were designed to ascertain whether the auditory evoked response in man reflects a tonotopic organization of the auditory cortex. In Experiment I, the evoked response (N 1 P 2 component) registered between vertex and earlobe, was measured when either 375,1000 or 8000 c/sec were presented simultaneously with 250 c/sec and when each tonal frequency was presented alone. In Experiment II, an 8000 c/sec tone intervened between successive presentations of a 250 c/sec tone. The question asked was whether the intervening 8000 c/sec tone would reduce the size of the response to the 250 c/sec tone. The results of Experiment I showed that for simultaneously presented tones the size of the evoked response increased progressively as the two tones became further removed from one another in frequency, and the size of the response amplitude evoked by the two tones which differed most in frequency (250–8000 c/sec) approached the sum of the response amplitudes evoked by each tone when delivered singly. In Experiment II, where tones were delivered sequentially, 8000 c/sec reduced the response to 250 c/sec when both tones were presented to the same ear. If, however, 8000 c/sec were given to the right ear and 250 c/sec to the left ear, no evidence for interaction between the two stimuli was apparent. Assuming that the N 1 P 2 component of the auditory evoked response can serve validly as an index of auditory cortex activity, the data support the notion that the auditory cortex is organized tonotopically but that each tonal frequency has widespread neural representation.

Simultaneous recordings from the auditory cortex and the cerebellar foliumtuber vermis of anesthetized and unanesthetized cats were obtained in response to pure-tone autitory stimuli. The auditory and cerebellar cortices both reflected frequency specificity in the awake animal. Changes in the orientation of awake animals to the sound source indicated that the cerebellar evoked potentials were highly sensitive to the directionality of the sound. Nembutal produced complete suppression of the cerebellar evoked potentials and enhancement (at higher stimulus intensities) of the auditory responses. Data indicate that the cerebellar vermis may play a major role in orienting the organism to the sound source by discriminating intensity differences between the two ears.

1. A short adaptation to sinusoidal flicker produces a temporary elevation in the temporal contrast threshold of a human observer. 2. The frequency specificity of this adaptation effect is much less than that observed with adaptation to spatial frequencies; thus it does not seem warranted to postulate the existence of distinct channels for the detection of specific temporal frequencies, as has been done in the case of spatial frequencies (Blakemore & Campbell, 1969). 3. At low frequencies, a substantial adapting modulation is necessary to produce an effect, but at high frequencies an effect can be seen even with adaptation which is below threshold (as determined by the method of adjustment). 4. This subthreshold adaptation appears to explain the observation that thresholds set by the method of adjustment rise by as much as a factor of two during the first minute of exposure. 5. No interocular transfer of the adaptation effect was observed. 6. Adaptation first appears at mesopic luminances, but its appearance is not dependent on the change from rod to cone vision. Under several conditions, however, the first appearance of flicker adaptation did coincide with a change in the deLange curve, which is attributable to the appearance of the antagonistic surround of visual receptive fields. Thus it was hypothesized that the surround is essential for adaptation.

Human electrocochleography is reviewed and the significance of the recorded potentials is discussed with special reference to the recording site. The response amplitude and threshold values for transtympanic AP recording are compared for various recording sites. The recorded AP amplitude varies with the inverse distance to the cochlear wall, resulting in an AP threshold increase which is nearly exponential with increasing distance from the cochlea.The click and tone-burst results arc compared with respect to frequency specificity and accordance with the subjective threshold. The Leiden method combining the promontory recording with short tone-bursts as stimuli proved to permit accurate determination of threshold for frequencies of 500 Hz and upwards, and provides detailed frequency-specific supraliminal information (e.g. about recruitment).

The apparatus developed in our department for electrocochleography is described. The principle of enhancement of a weak biological signal from background noise by an average response computer is elucidated, with indication of the limitations. The frequency content of the effective tone-burst sound stimulus was calculated to estimate the frequency specificity of the stimulus.A description is also given of the signal switching circuitry used to make separate recordings of CM and AP simultaneously. Some details are given of a circuit permitting rapid determination of AP threshold values and input-output curves with tone-bursts.Because the apparatus was developed to be applicable for experimental work and for auditory evoked response audiometry, several special features were incorporated. A circuit for accurate measurement of latency, a double-synchronized tone-burst generator, and a dB-linear intensity ramp with I’M bursts are briefly described.A flexible trigger generator provides many trigger modes...

This report extends previous observations on the acoustical dependencies of human brainstem evoked potentials. We report here on the effect of filtered continuous‐noise maskers on the latency and amplitude of click evoked responses. In condition 1, the masker high‐frequency cutoff is fixed at 20 kHz, while the low‐frequency cutoff varies from 16 to 0 kHz. Progressively extending the low‐frequency cutoff produces a decrease in amplitude and an increase in latency of wave V, the most reliably elicited response component. The response is abolished when the low‐frequency cutoff is at 2 kHz. In condition 2, the low‐frequency cutoff of the masker is fixed at 0 kHz while the high‐frequency cutoff is varied from 0.5 to 20 kHz. No latency or amplitude changes appear until the high‐frequency cutoff reaches 4 kHz, and the response is abolished at high‐frequency settings between 8 and 16 kHz. These experiments demonstrate that click‐evoked brainstem responses are generated by high‐ and middle‐frequency fibers, with very little contribution from low‐frequency fibers. The latency and amplitude shifts described above do not correlate well with the subjective threshold changes produced by the various maskers, but are better explained on the basis of traveling wave delays at the cochlear level.