Acoustic brainstem responses for clinical use: the effect of attention.

The acoustic brainstem response (ABR) is generally thought to be unaffected by variation in attention; however, recent papers suggest that during visual distraction of the subject wave Nv may be delayed. We have examined the ABRs of 22 normal subjects in states of auditory attention and visual distraction, using routine clinical testing procedures. We have shown that under these conditions altered attention states have no demonstrable effect on the latency of wave Nv.

Acoustic brainstem responses for clinical use: a comparison of pure tone stimuli with wide band clicks.

The acoustic brainstem response (ABR) in clinical use is generally elicited by a wide band click stimulus. This gives a well-synchronized response detectable at low sound intensities, but requires tedious biological recalibration which could be largely eliminated by the use of pure tone pip stimuli. We have therefore assessed ABRs in response to pure tone pips at 2 KHz and 4 KHz. This has shown that these tone pips elicit a much poorer response than clicks, having thresholds which are both significantly higher, and more widely distributed. We therefore conclude that wide band clicks remain the most satisfactory stimulus for clinical use.

A nine-year review of 841 children tested by transtympanic electrocochleography.

The case notes of 841 subjects who had had ECochG carried out between January 1972 and December 1980, were examined and the results compared with PTA results in 263 cases in which these were available. ECochG was found to be a good predictor of peripheral hearing as long as its limitations were recognized, and some of these are discussed. BSER, which has similar limitations, was also found to be a good predictor of peripheral hearing, although slightly less sensitive, and sometimes gave additional information on the hearing loss and the clinical state of the patient.

Evoked response audiometry and tomography - complementary procedures for the assessment of the deaf infant.

Evoked response audiometry and tomography of the ear both provide highly objective means of assessing certain types of deafness, but both require a general anaesthetic when used to investigate very young children. The use of evoked response audiometry (in particular electrocochleography and brain stem evoked response audiometry) and tomography as combined procedures using the same general anaesthetic is discussed in relation to 15 patients. Their ages ranged from 1 year 3 months to 16 years. All 15 had electrophysiological abnormalities in one or both ears. Abnormalities of the middle and/or inner ear were demonstrated by tomography in 12 patients and in 3 the tomography was normal. In 10 cases both procedures suggested severe or almost total deafness in one or both ears. The demonstration of an anatomical abnormality can be very important in future management with particular reference to surgical reconstructions and the potential development of cerebrospinal fluid fistula.

Brainstem electric responses and electrocochleography: a comparison of threshold sensitivities in children.

Brainstem electric response (BSER) and electrocochleography (ECochG) thresholds were measured in 55 ears of 46 'difficult-to-test' children. In most cases there was a reasonably close correlation between the two tests with BSER being less sensitive on the whole, but there was a small group, clinically indistinguishable from the majority, in whom an unacceptable discrepancy occurred. It was found that where the BSER threshold was equal to or less than 30 dB, the ECochG thresholds confirmed normal hearing, whereas if it was more than 30 dB further objective testing was essential to establish a definitive diagnosis of a hearing loss.

Signal statistics in objective auditory evoked potential (AEP) detection by the phase spectral method.

This paper reports on statistical aspects relevant to the use of the phase spectrum of post-stimulus EEG, in objective detection of the auditory evoked potential. The sampling statistics of two statistical estimators are discussed: the mean phase vector magnitude, and the standard deviation of an ensemble of post-stimulus EEG phases. These two estimators are circular statistics, and subject to strong sample size bias. Their confidence intervals have been derived empirically for sample sizes routinely used in clinical audiometry. A trial example illustrates the use of the objective phase statistics developed here; it is noted that the method may also be more efficient than the visual scoring of averaged responses.

Latency of brainstem response in children.

Brainstem electric responses were obtained on a group of 70 normal hearing children, aged 5-11 years, matched by age and sex. The recordings were examined for differences in latencies between the sexes at each age. The results showed that males have a longer latency than females, but when broken down into age groups, the latency of children aged 5-7 years was the same, and the latency of children aged 8-11 years differed. The results for latency of wave V of the whole group showed the greatest difference. The reason why such a sex difference should occur in middle childhood is discussed, but no physical cause found.

Fully objective ERA by phase spectral analysis.

A method of ERA using the Vertex potential is presented which is entirely objective. The result is given by means of a statistical evaluation which is derived automatically. The method is based on pattern analysis of the V-potential, the technique relying essentially on analysis of the phase spectrum of the appropriate Fourier components.

Temporary threshold shift, loudness, and auditory evoked potentials.

TTS2 of 20dB was produced in a group of subjects using a 1000 Hz pure tone. All TTS and related measurements were made at 1500 Hz. The recovery of TTS, and of TLS or 'temporary loudness shift' (measured against a reference tone at 20db, 40dB and 60dB SL in the opposite ear), as well as N1-P2 amplitude of the Vertex potential, were plotted. There was an orderly recovery of both TLS and TTS although the rate of recovery of the latter was noticeably more rapid. Recovery of N1-P2 amplitude was much less orderly, although it did recover in much the same way. When the amplitudes were measured at 40dB SL the recovery was more orderly and followed the course of TTS more closely. It was concluded that any relation between N1-P2 amplitude and growth of loudness was indirect.

Pattern analysis of auditory-evoked EEG potentials.

A pattern analysis approach to the detection of auditory evoked potentials in the EEG is reported. Pattern aspects of individual post-stimulus responses have been examined first through their correlation coefficients using the suprathreshold average evoked potential as a reference pattern, and second by the ensemble distribution of phase values of Fourier spectral components, employed to characterise signal pattern. The correlation study indicated that suprathreshold stimuli act to increase the reference pattern similarity of individual records. Individual harmonic phase values are distributed approximately uniformly for unstimulated EEG, but were demonstrated to be increasingly aggregated for increasingly suprathreshold stimuli. It is proposed that a fully objective audiometric technique can be based on a phase-spectral technique.

Differences in brainstem response latency with age and sex.

Brainstem evoked potentials in response to clicks at 60dB, 70dB and 80dB were recorded from a group of 70 normally hearing subjects. There were 10 subjects (5 male, 5 female) for each of the decades from the second to the eighth. The youngest subject was 14 years, the oldest 79 years. The possibility of there being increased latencies as a function of age was examined. The results indicated that there was, for practical purposes, no such increase. On the other hand there was very strong evidence that in females latenceis are shorter than in males. In addition, amplitudes were reduced in the case of older subjects. Condifidence limits for latency were calculated. These may be helpful in deciding whether or not a particular latency is outside the normal range.

Relation between the waveform of the cochlear whole nerve action potential and its intensity function.

The whole-nerve action potential (AP) was recorded by intracochlear electrodes in the guinea-pig. As is well known, in normal conditions, the AP elicited by tone bursts displays negative and positive deflections. Inactivation of the central end of the nerve at the internal auditory meatus (IAM), by introduction of a few drops of KC1 solution, or by mechanical pressure, produces a change in the wave shape of AP which is transformed into a single negative deflection. The relation of the amplitude of the monophasic AP to the intensity of the tone burst is monotonic, in contrast to the classical two-slope variation observed in normal conditions. These results are interpreted by the disappearance of a positive component of the response produced at the IAM. The convolution of the monophasic unit AP would explain the monotonic intensity function.