Electronystagmographic studies of small vertical fixation movements.

Statistical estimates of the accuracy with which electronystagmography (ENG) can provide eye movement records have been published by Shackel (1960). His data described horizontal eye movements over a fairly large displacement, as did data from trials comparing this technique with eye movement films described by Hoffman, Wellman, and Carmichael (I939) and Michael and Melvill Jones (I966). Elsewhere, Shackel and Davis (1960) demonstrated that monocular vertical potentials were only about 6o per cent. of the magnitude of binocular horizontal potentials, which inferred that a vertical eye movement may yield a signal with a poorer signal-to-noise ratio than a comparable horizontal one. In the opinion of Miles (939), who presented no supporting data, this vertical potential may possibly be enlarged if the eyes are closed. Vertical fixation movements could still be particularly difficult to measure accurately, however, because of an eyelid artefact which can confuse the vertical eye movement record (Barry and MIelvill Jones, I965). The aim of the present investigation was to perform a test-retest reliability examination of ENG records, when such records were made from small vertical eye movements. A comparison between the eye open eye closed case was also included.