[Electrophysiologic evaluation of the frequency selectivity by conversion of concurrent waves with the aid of a 40 Hz...

We have realized electrophysiological tuning curves by the "tone on logon" method at the 500, 1000 and 2000 Hz frequencies among thirteen normal hearing adults. We describe a simple method of electrophysiological frequency selectivity assessment by measuring the percentage of the wave amplitude recovering when a masking pure tone of varied frequency but constant intensity is sent together with the stimulus. Our stimulus had either a constant duration (10 ms) or a constant form (five cycles) for each frequency. We have studied and compared the tuning curves obtained with each kind of stimulus for the following parameters: the narrowness of the curve and the likeness between the tested frequency and the curve tip. One studied the latency of the potential obtained when the stimulus is sent together with a masking pure tone. A tone frequency lower than the stimulus brings about a latency decrease and a higher one, a latency increase. Our results show no difference between each kind of stimulus and show that the evoked response is the one of a narrow and specific part of the cochlear partition.