K. Jaureguirenaud et al., OTOLITH AND SEMICIRCULAR CANAL CONTRIBUTIONS TO THE HUMAN BINOCULAR RESPONSE TO ROLL OSCILLATION, Acta oto-laryngologica, 118(2), 1998, pp. 170-176
Three normal human subjects were oscillated about their naso-occipital
asis in a supine position at 0.4 Hz and 0.1 Hz. both in darkness and
in the light with a structured fixation target. The same subjects were
oscillated in roll about an upright position, at the same frequencies
, in darkness; and also about axes directed 20 degrees and 40 degrees
to the left and to the right of the midsagittal plane, itt 0.4 Hz, in
darkness. Three-dimensional binocular eve movements were recorded usin
g video-oculography. All stimuli induced a predominantly torsional nys
tagmus with small disconjugate head-vertical (skew) and conjugate head
-horizontal components. For roll oscillation, the torsional sieve phas
e velocity gain ii-as higher in the light and generally increased with
rile stimulation frequency. In darkness, only one subject had signifi
cantly higher torsional gains in the upright compared to the supine po
sition (12% difference), suggesting that the otolith contribution to t
ile roll response is minimal at the frequencies tested. The slow phase
velocity gain of the skew increased with fixation in two subjects, bu
t decreased in the third subject: these changes were related to change
s in eye vergence. In the upright position, with oblique axes of rotat
ion. the head-vertical eye movements were asymmetrical, with the outer
most eye executing a larger amplitude movement. The disconjugate head-
vertical eye movements observed can be explained by the pattern of ver
tical semicircular canal stimulation and their connections to the extr
aocular muscles. In humans, skewing of tile eyes may compensate for th
e eccentricity of the foveae which lie in the temporal retina and unde
rgo vertical translations in opposite directions when the eyes tort.