Abstract
Ten samples of the averaged spontaneous brain activity were made on a sleeping child of 5 years old. On the other hand, from a typical pattern of the averaged evoked response, 5 samples with different amplitudes were prepared. Then each of the 10 samples of the spontaneous activity and each of the 5 samples of the evoked response were composed by using an averaging computer. Two trained examiners independently made the determination of the presence or absence of the evoked response on 41 out of 50 composed samples and 10 samples without evoked response. The decision was also attempted according to an objective standard made by one of the authors. Besides, peak latencies of P2 and N2 as well as P2N2 amplitude were measured on 19 composed samples.
Results obtained were summarized as follows:
1. There was an individual discrepancy between the examiners as to the detectability of the response.
2. False positive decision occured in about 10 to 35 per cent of the judgements.
3. Almost 100 per cent detection of the response Was achieved when the amplitude of the evoked response was twice as large as the levels of the averaged background activity.
4. The range of so-called “trasition zone” of the evoked response was estimated to cover the range of the stimulus intensity of 40 to 50dB or more.
5. The latencies and amplitudes of the evoked response were modified considerably by the background activity.
