Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. I. Normative measures.

Three-channel Lissajous' trajectories (3-CLTs) of auditory brainstem evoked potentials (ABEPs) were obtained from 14 humans (28 ears) in response to 75 dB nHL, 10/sec alternating polarity clicks. A normative set of 3-CLT quantitative measures was calculated and compared with amplitudes and latencies of the simultaneously recorded, single-channel, vertex-mastoid ABEP. The comparison included average values as well as intersubject variability. The 3-CLT measures included: apex latencies; planar segment durations, orientation, size and shape; trajectory-amplitude peaks and their latencies. Apex latencies of 3-CLT were comparable to peak latencies of the vertex-mastoid records, both in absolute values and in intersubject variability. Durations of planar segments were approximately 0.7 msec and their standard deviations were about a half of their average. Individual planar segment orientations were typically within 50 degrees of the normative average. Trajectory amplitudes were, in general, somewhat larger than peak amplitudes of the vertex-mastoid records, while their intersubject variabilities were comparable. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. The quantitative study of the 3-CLT of auditory brain-stem evoked potentials will enable evaluation of normal, as well as pathological, evoked potentials, to further the understanding and utility of this comprehensive representation of brain-stem function.