Brain-stem responses when masking with wide-band and high-pass filtered noise

Investigations, using click stimuli masked by wide-band and high-pass filtered noise with cut-off frequencies of 2 600, 1 250 and 850 Hz were carried out. The latency shift of a response evoked by a click of 60 dB HL and wide-band masking at 80 dB HL is 0.2 - 0.3 ms for wave I and about 0.6 ms for wave V. The results obtained with high-pass masking at various cut-off frequencies differ distinctly from those found by other authors. For instance, when using high-pass masking noise of a lower limiting frequency of 850 Hz and levels of 85 and 90 dB no clear brain-stem responses were discernible. Therefore, the appearance of the brain-stem responses with masking noise at various frequency limits and at various levels was examined. With high-ass noise masking at decreasing cut-off frequencies from 1 800 Hz down to 600 Hz and increasing noise levels, wave V disappears with a slight latency shift, but subsequently to wave V an additional wave occurs which remains stable even in the case of high noise intensities. Further studies are necessary to clarify the properties of this additional wave.