Components of disparity vergence eye movements: application of independent component analysis

The "dual mode" theory for the control of disparity vergence eye movements states that two control components, a preprogrammed "transient" component and a feedback-controlled "sustained" component, mediate the motor response. Although prior experimental work has isolated and studied the transient component, little is known of the sustained component's contribution to the dynamic vergence response. The timing between the two components and their relative magnitudes are of interest as they relate to the strategies used by the brain to coordinate and control the two components. Modeling studies provide an estimate of component magnitudes, but cannot uniquely identify component timing nor can the provide detailed information on component dynamics. Here, an eigenvector analysis is applied to a multivariate data set consisting of multiple responses to a step stimulus to confirm the presence of two major components in the vergence response. Next, a new application of independent component analysis is used to estimate the activation patterns of the two components. Results from five subjects show that the sustained component is activated concurrently with the transient component, dominates the later portion of the response, and maintains final position.