Tuning of Binocular Fusion by Ocular Proprioception: A Model

Proper binocular alignment requires intact visual, motor, and proprioceptive signals. It is hypothesized that the eye position signal in the brain is ocular proprioception. Animal models have revealed that it is an important factor in the development and maintenance of interocular alignment. For example, elimination of this signal by lesioning the ophthalmic division of the trigeminal nerve (V1) leads to the development of strabismus. Experiments that inactivated cortical ocular proprioception caused a reduction in convergence during fixation. The empirically determined horopter known as Panum's area of fusion can help us understand this scientific observation. For any given binocular fixation point, Panum's area in 3D space is defined as the area where all objects appear in stereovision. Objects existing outside of this area appear as double images which the cortical visual disparity system uses for generating new targets to make vergence eye movements. If Panum's area is enlarged, then more objects will be in apparent stereovision and the oculomotor system will no longer be able to execute vergence eye movements to these objects. We present a model where Panum's area is modulated by an eye position signal and that this model's output is compared with monkey vergence data where the eye position signal is inactivated.