The envelope following response to multiple tone pair stimuli

The envelope following response (EFR) is a steady-state evoked response which follows the envelope of a stimulating waveform. A tone pair with frequencies f1 and f2 generates a temporal envelope whose period corresponds to the difference in frequency between the constituent tones (f2-f1 = f2,1). EFRs were recorded from Mongolian gerbils using amplitude-modulated stimuli comprised of from 1 to 4 tone pairs. Five stimulus tone pairs were used having center frequencies of approximately 0.3, 1, 2, 3, and 5 kHz; their corresponding envelope frequencies were approximately 38, 55, 66, 85, and 142 Hz. The magnitude of the EFR to each tone pair was measured separately and in combination with other simultaneously presented tone pairs. Small decreases (1-3 dB) in response magnitude, relative to the single tone pair condition, resulted from the addition of 1-2 tone pairs of higher frequencies; this effect was more pronounced with the addition of a third and fourth tone pair. However, the addition of the 300 Hz tone pair resulted in the significant enhancement of the response to higher frequency tone pairs. These data indicate that multiple tone pair EFRs may be a useful technique for the rapid acquisition of frequency-specific audiometric information.