Search for normality criteria of auditory brain responses and auditory steady state response with free-field...

To discover the thresholds of normality of the tests of ABR and ASSR in free-field stimulation compared with headphones.

Descriptive study of a series of cases of children without hearing loss carried out between April 2016 and January 2017. The ABR and conventional ASR were performed using insert headphones and free-field stimulation.

Fifty-four ears were evaluated with absolute criteria of normality. The mean age was 16.7 months (SD=5.7). The evocation of the action potential at 70 dBs in the free-field showed a mean on wave I of 3.47ms, on wave II of 4.01, on wave III of 5.97, on wave IV of 6.71 and on wave V of 8.22. There is a statistically significant difference (p<.05) between the value obtained with insert earphones and the free-field on wave I (mean difference 1.91), on wave III (1.88), on wave IV (1.69) and on wave V (1.95), their being higher in stimulus in free field. There were no statistically significant differences in the interlatencies. The responses in the ASSR with free-field showed an increase of 1.56minutes compared to the headphones.

The thresholds obtained in ABR by free-field were differentiated from those obtained by headphones in the increase of latencies, caused by delayed stimulation of the ear due to the distance between the sound source and the eardrum. Both tests are feasible by free-field stimulation, which would allow them to be applied routinely to patients on whom conventional tests cannot be performed.