High-Pass Digital Filtration of the 40 Hz Response and its Relationship to the Spectral Content of the Middle Latency and 40 Hz Responses

Abstract

This study analyzed the effects of high-pass filtration on the 40 Hz response using zero and standard phase shift digital filtration. Filtration effects were compared to the spectral content of the middle latency response (MLR) and 40 Hz response. The spectral composition of the MLR was found to contain major response energy at 10 and 40 Hz. The major energy of the 40 Hz response was at 40 Hz with minor peaks every 40 Hz above the fundamental frequency. The elimination of the 10 Hz response energy in the 40 Hz response was due to cancellation caused by phase differences which occurred in the production of a steady state potential. The reduction was confirmed by the minor amplitude effects created by zero-phase-shift high-phase filtration (cutoff frequency 30 Hz with 36 dB/oct slopes) on the 40 Hz response as compared to the MLR. The only beneficial effect of high-pass filtration was the elimination of the mild undulation of the unfiltered waveform. The major effect of phase-shift high-pass filtration on the 40 Hz response was the displacement of the high frequency ABR from the peak to the descending slope and finally to the trough of the MLR. Shifting of the ABR from the peak of the MLR resulted in amplitude loss which may affect response identification at threshold. The authors recommend minimal highpass filtration (i.e., less than 12 dB/oct slope and a cutoff frequency less than or equal to 15 Hz) when recording the 40 Hz response. The spectral analysis of the evoked response may be able to predict the optimal rate for eliciting a steady state response in divergent subject populations.

Improved Electrically Evoked Auditory Steady-State Response Thresholds in Humans

“…In this case, the spectrum of the stationary response can be explained as the product of a dirac comb with the spectrum of the transient response, i. e., it is equal to the sampling of the transient spectrum at the modulation frequency and its harmonics. Spectral analysis of MLRs shows a maximum around 40 Hz, with a smaller peak around 90 Hz corresponding to the observed second harmonic (Suzuki et al 1983;Kavanagh and Domico 1986). Similar observations can also be made for acoustically evoked ASSRs to modulated sine tones, with a peak around 80 to 90 Hz (Picton et al 2003).…”

On the cyclic nature of perception in vision versus audition

“…(b) When the white noise stimulus sequence encodes the changing loudness of an auditory pure tone (1000 Hz carrier frequency), the transient broadband response is present, but no subsequent reverberation is observed in any frequency range. The increasing width of the transient response above30 Hz is likely due to the auditory middle latency response (MLR)[90], a short-lived auditory potential (,50 ms) which appears smeared in time owing to our wavelet time -frequency transform (using an eight-cycle window length at50 Hz). The same 12 subjects participated in the visual and auditory experiments.…”

Analysis of Auditory Evoked Potentials by Magnitude-Squared Coherence

“…In addition, significant coherence was present for the modulating frequency (40 Hz), its 2nd and 3rd harmonics, and the frequencies 960, 1000, and 1040 Hz. Response energy at overtones of the envelope and component frequencies has been noted before for both 40 Hz (Kavanagh & Domico, 1986) and FFR (Davis & Britt, 1984;Snyder & Schreiner, 1984. Interpretation of these nonlinearities requires some discussion of the concept of an envelope.…”