Individual differences in auditory electric responses: comparisons of between-subject and within-subject variability....

Each of two groups of adult subjects was tested under a repeated-measures design (Lauter & Loomis, 1986, 1988; Lauter & Karzon, 1990a, b) for ABRs and one other set of responses: middle-latency responses (MLRs: 10 to 50 ms post-stimulus) from Group II (four females and four males), and late responses (50 to 300 ms post-stimulus) from Group I (four females and three males). A companion paper (Lauter & Karzon, 1990b) presents data comparing and contrasting the patterns of relative variability of waveform-peak latency observed in middle-latency, late responses, and the ABR data previously reported. This paper presents amplitude results for the same data sets. Our findings indicate that, as we have reported previously, with regard to between-subject vs. within-subject variability of peak parameters of auditory EP waveforms, normal adult subjects are more consistent when compared with themselves than when compared with each other. This is true at all auditory EP levels tested, from brainstem to cortex, and is observed in both amplitude and latency data, in spite of the fact that the actual values of amplitude-stability measures are an order of magnitude smaller than for latency stability.