[The optimal stimulation parameters of the free-field auditory steady-state responses]

Studies of the recent years are devoted to using the auditory steady-state responses (ASSR) as an evaluation method of amplification outcomes. In this case stimulation is performed in the sound field via loudspeaker with a hearing aid (HA) in patient's ear.

Estimation the optimal stimulation parameters of ASSR in free field, which provide maximum correlation with behavioral thresholds.

26 subjects were included in the study: 10 with normal hearing (4 adults and 6 children) and 16 children (1-16 years old) with sensorineural hearing loss (SNHL). Aided and unaided ASSR thresholds were compared with corresponding behavioral thresholds (BT). All recordings were conducted in free sound field. We used mono-frequency stimulation method at 500-4000 Hz career frequencies. Modulation frequency was set as 40 Hz. Types of stimuli modulation: AM/FM modulation, exponential modulation (AM²), three carrier frequencies and modulated Chirp-tone (Chirp).

In normal hearing subjects the difference between ASSR and BT varied from 0 dB to 35 dB, and the significant correlation between them was observed (p<0.05). The maximum difference between ASSR and BT in children with SNHL was at 500 Hz (15.6±4.3 dB), minimum - at 2 and 4 kHz (8±2.9 dB and 7±3 dB respectively). In aided condition maximum difference was detected at 500 Hz (10.2±3.8 dB), minimum - at 1 and 2 kHz (7.8±2.8 and 7.3±3.1 dB respectively). We got significantly less difference between ASSR and BT in all test conditions using following types of stimuli: at 500 Hz and 1000 Hz - AM² (p<0.01); at 2 and 4 kHz - Chirp (p<0.05 and p<0.01 respectively). Thereby, free field ASSR might be used as an objective method of evaluation the amplification outcomes in children with SNHL.