Neural processing in vergence eye movements: a time based study

Inward turning of the two eyes, termed disparity vergence, sometimes exhibits two closely-spaced, fast dynamic movements. These response doubles can provide information on the neural processes that control the fast, dynamic response. The second component of this pair could be generated by either an internal process or by external error from visual feedback. To differentiate between these two mechanisms, a comparison was made between doubles induced experimentally (using a "forced-error" protocol) and those that occur naturally in standard step responses. The two stimulus conditions produced response doubles with different timing properties. Since the forced-error doubles were generated by visual feedback, differences in timing imply that normally occurring double responses are mediated by an internal mechanism. This internal feedback mechanism is likely to be involved in the production and control of the fast dynamic portion of all vergence eye movements.