Effect of Different High-Pass Filters on the Long-Latency Event-Related Auditory Evoked Potentials in Normal Human Subjects and Individuals Infected with the Human Immunodeficiency Virus

The effect of different high-pass filters on long-latency auditory evoked potentials was investigated in 25 subjects, 15 of whom were asymptomatic individuals seropositive for the human immunodeficiency virus (HIV) and 10 of whom were normal control subjects without known risk factors for HIV infection. High-pass filtering was done simultaneously at 0.25 Hz and 1.0 Hz, and cerebral responses to rare (2,000 Hz) and frequent (1,000 Hz) tones were recorded from Fpz, Cz, and Pz electrode placements and averaged separately. Using either filter, well-formed and reproducible responses were obtained, although the latencies of the N1, P2, N2, and P3 components of the response were slightly shorter when a 1.0 Hz filter was used. In addition, the appearance of the late response was modified in a manner suggesting that components of the ERP considerably slower than P3 were being attenuated by a 1.0-Hz filter. Although it could be argued that this makes the use of a 1.0-Hz filter setting preferable in the clinical setting, the variability and reproducibility of the ERP were comparable when either high-pass filter was used, and both resulted in similar findings in the HIV-infected individuals compared to normals.