The Use of a Frequency Scrambling Technique in Electric Response Audiometry

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Abstract
Two problems beset Evoked Response testing in infants. The first is, that it may only be possible to keep the subjects quiet for short periods. The second is one of habituation. A method of testing was devised to overcome some of the ramifications of these problems. This method produced at the same time a rapid sweep of the subject's thresholds at different frequencies and a reduced habituation, allowing a larger response to a given number of stimuli. This required the building and attachment of an electronic selector switch to the existing apparatus. This switch was made to produce a sequence of frequencies (0.5, 1, 2 and 4kHz) at small intervals, e.g. half-a-second. This sequence could be set at any desired intensity level, from 110dB to OdB I.S.O., and functioned so that the Evoked Response to each individual frequency could be separated from the rest on its own computer channel. Thus, in approximately two minutes, the subject received usually 256 stimuli, 64 of each frequency, the interval between tones of the same frequency being two seconds. Each frequency could also be linked to a different pair of EEG electrodes, so giving a spatial comparison of cortical activity.

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