Effects of click polarity on auditory brain-stem potentials: a three-channel Lissajous' trajectory study

Three-channel Lissajous' trajectories (3CLTs) of the auditory brain-stem evoked potentials (ABEP) were recorded from 16 adult subjects (28 ears) in response to rarefaction (R), condensation (C) and alternating polarity (A) clicks. 3CLTs were analysed and described in terms of their geometrical measures. All 3CLTs included 5 planar segments (named 'a', 'b', 'c', 'd' and 'e') whose latencies, durations, orientations, sizes and shapes were not affected by click polarity. Occasionally, planar segment 'd' was not defined, and its absence was parallelled by the absence of peak IV in the Vertex-Mastoid records. A small (0.03 microV), but significant increase was found in the trajectory amplitude of planar segment 'e' in C clicks. The effects of click polarity on 3CLT observed in this study suggest that some previously described ABEP changes with click polarity were the result of interactions between electrode positions and relative contributions of overlapping generators. The effects on the fourth and fifth ABEP components may be the results of changes in the temporal overlap of the activity of their generators.