Figure 1: A.
Photograph of the mechano-electrical averaging device designed by Dawson.3
With reduction gears, the motor rotated the spindle carrying the distributors
at 10 Hz; the distributors passed the electrical activity from the cortex to
a series of 62 capacitors every 10th revolution, following a stimulus. After
the procedure had been repeated the requisite number of times, the charge stored
on each of the capacitors during successive 100 ms epochs was read out, giving
the averaged response. An example, following ulnar nerve stimulation, is shown
for the contralateral and ipsilateral somatosensory areas in C (upper
and lower traces respectively). B (upper) shows an earlier method of
recording evoked potentials, in which photographic superimpositions of faint
traces were made, following median nerve stimulation at the wrist. The centripetal
impulse volley is recorded from the median nerve at the elbow (lower trace).
From Dawson2,3 with permission.
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