The auditory evoked Slow Vertex Response (SVR) has been used as one of the objective audiometry. However, there are some problems still remain unsolved, such as the false positive response especially in infants under sleeping stages and unstability of the response for low intensity stimuli near the audible threshold.
The aim of this paper is to establish a method to improve the detectability of the SVR, and the responses for 20dBSL both in adults and infants have been analized under a series of computerized procedures using PDP 11/60.
Methods were as follows;
(1) The non-recursive digital bandpass filter using the fast Fourie transform was applied for the SVR in adults and infants.
(2) Both non-filtered and digital filtered EEG were averaged 100 times. During these procedures, the averaged EEGs every 25 times were recorded successively, and their signal to noise ratio (S/N) were calculated, in order to analyse the modality of the response.
Results were as follows;
(1) The most effective pass-band of digital filter in order to detect SVR in adults and infants was 3 to 9Hz.
(2) The detectability of digital filtered SVR was increased by 18% in adults, 15% in infants, compared with the non-filtered SVR. The S/N of filtered SVR was significantly increased, compared with non-filtred SVR.
(3) The false positive response in digital filtered EEG in infants reduced by approximately 50%, compared with those in non-filtered EEG.
(4) Averaged EEGs every 25 times with low intensity stimuli were not always stable as for their latencies and amplitudes.
(5) The 25 times averaged EEG with the highest S/N was appeared 20 to 30 seconds after the first stimulus was applied. This phenomenon seemed to be influenced by the attention or habituation to the acoustic stimuli.
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