Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. II. Effects of click intensity

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEP) were recorded from 14 adult subjects at 15, 45, and 75 dB (nHL). The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus level. At 75 dB, 9 planar segments were observed, each having unique apex latency, boundaries, duration, shape, size and orientation in voltage space. As stimulus levels were lowered, changes were noted in apex latency and trajectory amplitude which parallelled changes seen under similar experimental conditions using single-channel ABEP. In addition, changes were seen in planar segment number, boundaries, duration, shape, size and orientation, all of which could be related to decreased generator activity. It is proposed that at high stimulus levels, there is significant temporal overlap of generator activity which results in a larger number of planar segments and single-channel peaks than at low stimulus levels. This may be important to the identification of the specific generators of the ABEP and their appropriate clinical usage.