The Auditory Stimuli to Evoke a clear Average Response at Behavioral Threshold

Abstract

One of the difficulties in evoked response audiometry is identification of the response at lower stimulus intensities. It was thought that frequency change could evoke the response somewhat independently of the intensity of the tone, and averaged responses evoked by frequency-modulated (FM) tones were studied in order to learn whether this stimulus was suitable as a stimulus for obtaining a clear response at threshold intensity

The typical response evoked by a FM tone, which was presented in a continuous pure tone of 1 000 Hz by changing its frequency at intervals, was characterized by there vertex positive and two negative waves, which were refered to as P₁, P₂, P₃, N₁, and N₂. The P₁, N₁, and P₂ peaks were the most prominent. The latency of the response decreased with both increase in frequency increment and increase in tone intensity. The P₁-N₁ and N₁-P₂ amplitudes increased with increase in frequency increment, and this increase was more conspicuous for tones of lower intensity. Amplitude increment with increasing tone intensity were also observed, but the increments were smallest for the condition of 200 Hz increment because of a large amplitude at O dB SL intensity

This study revealed that an FM tone of 20% increment could evoke a clear discernible response at threshold intensity in all subjects. Thus, the FM tone is very advantageous for evoked response audiometry, although the hearing sensitivity at a very exact frequency is not indicated

Key Words:

• Electric response audiometry (ERA)
• Cortical evoked potentials
• Frequency-modulated tones
• P₁-N₁, N₁-P₂ amplitudes
• P₁, N₁, P₂ peak latencies