Three-channel Lissajous' trajectory of auditory brain-stem potentials evoked by specific frequency bands (derived responses).

Three-channel Lissajous' trajectories (3-CLT) of the auditory brain-stem evoked potentials were recorded from 14 adult subjects in response to different frequency bands as well as to unmasked clicks. The frequency bands (8 kHz and above, 4-8 kHz, 2-4 kHz, 1-2 kHz and 1 kHz and under) were obtained by subtraction of wave forms to clicks with high-pass masking at these frequencies (derived responses). The 3-CLTs were analysed and described in terms of their geometrical measures. All 3-CLTs included 5 planar segments whose latencies progressively increased with decreasing stimulus frequency, and whose durations and orientations did not change across frequencies. Apex trajectory amplitudes as well as planar segment sizes decreased between unmasked clicks and specific frequency bands, and with decreasing frequency. The changes noted for apex latency and trajectory amplitude were paralleled with corresponding changes in amplitude and latency of single-channel records. The changes in 3-CLT measures with changes in stimulus frequency reflect the contribution of different parts of the cochlea. The unchanged measures may be attributed to the unchanged anatomy of the generators under the different stimulus conditions. The results of this study do not support the wide band of stimuli as responsible for the planarity of 3-CLT segments. In addition, these results indicate that different cochlear processes are responsible for the latency changes observed across stimulus intensities and for those associated with stimulus frequency.