Abstract
In pure symmetrical vergence eye movements, a fusion initiating component quickly brings the eyes close to the desired position. A small error usually remains after this response which must be corrected to attain the small final vergence error (i.e., fixation disparity). Error correction will usually involve both version and version movements so possible mechanisms include: small saccades, smooth pursuit, symmetrical vergence, or some combination. Alternatively, an asymmetrical vergence or uniocular slow eye movement could be used to achieve the highly precise final position. Saccade-free late fusion sustaining components during the steady state to a symmetrical vergence step stimulus are analyzed using independent component analysis. Results suggest that fine correction is most likely the product of closely coordinated version and vergence components.
Highlights
Pure vergence stimuli fall strictly along the midline or “cyclopean” axis and while rare in natural viewing, are easy to create in the laboratory
The oculomotor response to asymmetrical stimuli has been the subject of much controversy, but has largely formed around two camps: one favoring Hering’s Law (1977) which postulates independent control processes for version and vergence movements and the other centered around Helmholtz’s arguments (1962) for a learned behavior based on independent control of each eye
The input to the algorithm was the left and right eye movements, but as noted above, any mixture of left and right eye movements gives the same result since the algorithm begins with a random mixture anyway
Summary
Pure vergence stimuli fall strictly along the midline or “cyclopean” axis and while rare in natural viewing, are easy to create in the laboratory. They are useful for studying the neural control of disparity vergence eye movements. Responses to such stimuli should not contain version components, but two factors can lead to transient version components during a symmetrical vergence response. Even if no saccades are present, responses to pure vergence stimuli are often asymmetrical because one eye moves faster than the other during the fusion initiating. The oculomotor response to asymmetrical stimuli has been the subject of much controversy, but has largely formed around two camps: one favoring Hering’s Law (1977) which postulates independent control processes for version and vergence movements and the other centered around Helmholtz’s arguments (1962) for a learned behavior based on independent control of each eye
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