Journal of Neuroscience, Vol 7, 2576-2589, Copyright © 1987 by Society for Neuroscience
Optically induced changes in the couplings between vergence and accommodation
FA Miles, SJ Judge and LM Optican
Vergence-induced accommodation (V-A) and accommodation-induced vergence
(A-V) were measured in human subjects before and after they had worn
various optical devices for 30 min. Laterally displacing periscopic
spectacles, which increase the required change in vergence per unit change
in accommodation, caused decreases and increases in the gain of V-A and A-V
responses, respectively. These observations are consistent with the view
that the gain of the neural cross-linkages between vergence and
accommodation are subject to adaptive regulation. However, there were
strong asymmetries: Medially displacing periscopes (cyclopean spectacles),
which reduce the required change in vergence per unit change in
accommodation to zero, were almost totally without effect. Base-out prisms,
which increase the required convergence by an amount that is constant for
all viewing distances, caused downward and upward shifts in the V-A and A-V
response curves, respectively. Base-in prisms, which reduce the required
convergence by a constant amount for all viewing distances, caused downward
shifts of A-V curves but had no significant effect on V-A curves. These
effects of prisms are in essential agreement with the work of others and
confirm the existence of adaptive elements that regulate the bias in the
vergence and/or accommodation control systems. Secondary effects of wearing
periscopes and prisms indicated a certain lack of specificity in the
sensing of gain and bias errors: vertical shifts of V-A and A-V curves
(resembling those seen with base-out prisms) often occurred with the
laterally displacing periscopes, and gain changes (generally resembling
those seen with laterally displacing periscopes) often occurred with the
base- out prisms.