Amplitude and phase equalization of stimuli for click evoked auditory brainstem responses

Abstract

Although auditory brainstem responses (ABRs), the sound-evoked brain activity in response to transient sounds, are routinely measured in humans and animals there are often differences in ABR waveform morphology across studies. One possible reason may be the method of stimulus calibration. To explore this hypothesis, click-evoked ABRs were measured from seven ears in four Mongolian gerbils (Meriones unguiculatus) using three common spectrum calibration strategies: Minimum phase filter, linear phase filter, and no filter. The results show significantly higher ABR amplitude and signal-to-noise ratio, and better waveform resolution with the minimum phase filtered click than with the other strategies.

Aging effects on the binaural interaction component of the auditory brainstem response in the Mongolian gerbil: Effects of interaural time and level differences

“…3). Such differences could be due to differences in the electrode placement (Beattie and Taggert, 1989; Dum et al, 1981), stimulus types (the previous study used tone pips whereas a click was used in the present study) or calibration (Beutelmann et al, 2015). The present study used a click since in human subjects it elicited a larger absolute BIC amplitude in comparison to the BIC observed for tone pips (Ito et al, 1988).…”

“…1) had a duration of about 33 μs (equivalent rectangular duration, measured acoustically, 20.8 μs electrically) and a flat frequency spectrum between 1 and 24 kHz. The most important component of a click stimulus is the steep onset to elicit a strong and clear ABR signal (Beutelmann et al, 2015). Therefore, the signals were filtered by a 128 th order minimum phase FIR filter before presentation, which equalizes the amplitude spectrum and compresses the impulse response duration at the ear canal entrance.…”

“…Therefore, the signals were filtered by a 128 th order minimum phase FIR filter before presentation, which equalizes the amplitude spectrum and compresses the impulse response duration at the ear canal entrance. The setup and generation of the stimuli were described in detail in (Beutelmann et al, 2015). Briefly, sampling rate for playback and recording of responses through an RME Hammerfall Multiface II sound card was 48 kHz.…”

“…The click stimuli were amplified by a Harman-Kardon HK6350 amplifier and presented by Vifa XT300/K4 speakers. The speakers were coupled to the ear canal of the gerbil by a custom built combination of exponential (100 mm length) and conical (20 mm length) horns (for detail of system calibration see Beutelmann et al, 2015). Acoustical crosstalk was measured between both speakers and the corresponding opposite Etymotic ER-7C probe microphone positioned at a place 2 mm into the ear canal.…”

“…In the second step, the weights are calculated after subtracting the first step average from each interval. Details on the signal processing are presented in Beutelmann et al, 2015.…”