Slow evoked cortical potentials from ten young normal-hearing subjects have been recorded as responses to linear frequency ramps of a continuous pure tone. Frequency changes from 10 to 500 Hz were studied; the rate of frequency change was varied from 0.02 to 50 kHz/s while the duration of the change was varied from 10 to 500 ms. The rate of frequency change was shown to have the greatest bearing on the responses except for frequency ramp durations below 50 ms and frequency changes below 50 Hz. The base frequencies (250-4000 Hz) and sound levels (20-80 dB HL) exerted an influence on the evoked responses that was qualitatively similar to their influence on behavioral thresholds. The direction of the frequency sweep had no significant influence on the evoked responses. A functional model is proposed in which the time derivate of the signal frequency is integrated with an adaptable integration time that is controlled by the rate of the frequency change.

Ten normal-hearing subjects were evaluated with both manual and computer controlled audiometry using the ascending threshold determination method as proposed by ISO. The study shows that the thresholds obtained with the two different techniques correlate well and that standard deviations for the test--retest difference are significantly lower in the computer-controlled situation. The results also indicate that computer-controlled audiometry may be of importance in general clinical applications giving rapid and reliable threshold determination.

With the purpose of comparing test-retest reliability, pure-tone audiometry with a step size of 2 and 5 dB using the ascending technique was performed on two groups of subjects. One group consisted of 10 normal-hearing subjects and the other of 10 subjects with moderate cochlear hearing loss. The statistical analysis of the overall estimation of standard deviation obtained with the different step sizes showed no significant difference in any group. However, at 3 000 and 4 000 Hz in the cochlear group a significantly lower standard deviation was obtained with the smaller step size. The number of threshold crossings required to fulfil the threshold criterion increased significantly with the smaller step size.

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