Error Correction in Vergence Eye Movements: Evidence Supporting Hering’s Law

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

Binocular Eye Movements Are Adapted to the Natural Environment.

Humans and many animals make frequent saccades requiring coordinated movements of the eyes. When landing on the new fixation point, the eyes must converge accurately or double images will be perceived. We asked whether the visual system uses statistical regularities in the natural environment to aid eye alignment at the end of saccades. We measured the distribution of naturally occurring disparities in different parts of the visual field. The central tendency of the distributions was crossed (nearer than fixation) in the lower field and uncrossed (farther) in the upper field in male and female participants. It was uncrossed in the left and right fields. We also measured horizontal vergence after completion of vertical, horizontal, and oblique saccades. When the eyes first landed near the eccentric target, vergence was quite consistent with the natural-disparity distribution. For example, when making an upward saccade, the eyes diverged to be aligned with the most probable uncrossed disparity in that part of the visual field. Likewise, when making a downward saccade, the eyes converged to enable alignment with crossed disparity in that part of the field. Our results show that rapid binocular eye movements are adapted to the statistics of the 3D environment, minimizing the need for large corrective vergence movements at the end of saccades. The results are relevant to the debate about whether eye movements are derived from separate saccadic and vergence neural commands that control both eyes or from separate monocular commands that control the eyes independently.SIGNIFICANCE STATEMENT We show that the human visual system incorporates statistical regularities in the visual environment to enable efficient binocular eye movements. We define the oculomotor horopter: the surface of 3D positions to which the eyes initially move when stimulated by eccentric targets. The observed movements maximize the probability of accurate fixation as the eyes move from one position to another. This is the first study to show quantitatively that binocular eye movements conform to 3D scene statistics, thereby enabling efficient processing. The results provide greater insight into the neural mechanisms underlying the planning and execution of saccadic eye movements

Binocular coordination of eye movements – Hering’s Law of equal innervation or uniocular control?

The neurophysiological basis for binocular control of eye movements in primates has been characterized by a scientific controversy that has its origin in the historical conflict of Hering and Helmholtz in the 19th century. This review focuses on two hypotheses, linked to that conflict, that seek to account for binocular coordination – Hering’s Law vs. uniocular control of each eye. In an effort to manage the length of the review, the focus is on extracellular single‐unit studies of premotor eye movement cells and extraocular motoneurons. In the latter half of the 20th century, these studies provided a wealth of neurophysiological data pertaining to the control of vergence and conjugate eye movements. The data were initially supportive of Hering’s Law. More recent data, however, have provided support for uniocular control of each eye consistent with Helmholtz’s original idea. The controversy is far from resolved. New anatomical descriptions of the disparate inputs to multiply and singly innervated extraocular muscle fibers challenge the concept of a ‘final common pathway’ as they suggest there may be separate groups of motoneurons involved in vergence and conjugate control of eye position. These data provide a new challenge for interpretation of uniocular premotor control networks and how they cooperate to produce coordinated eye movements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86996/1/j.1460-9568.2011.07695.x.pd

Assessment of Dual-Mode and Switched-Channel Models with Experimental Vergence Responses

Controversy exists in the literature regarding the basic neural control structure that mediates convergence responses. This study constructed and simulated two models, the switched-channel feedback model and the dual-mode model consisting of preprogrammed with feedback control. Models were constructed and compared to experimental data. The stimuli consisted of 2 deg and 4 deg vergence steps. Both closed- and open-loop settings were utilized. After parameter adjustment, both models could accurately simulate step responses from subjects having a range of response dynamics. The model with a preprogrammed element required less parameter modification when stimulus amplitude changed. Both models could accurately simulate some attributes of vergence; however, neither model could represent the modifications commonly observed within the transient portion of the vergence response

Sensorimotor integration processing in Diabetic Retinopathy and Diabetic Peripheral Neuropathy

This study evaluated the direct link between visual perception and related motor output responses during an optic flow stimulation which induced a perception of forward movement, and during a driving task using a simulator. The experiments focussed on the evaluation of two different complications of diabetes, diabetic retinopathy and diabetic peripheral neuropathy (DPN), in order to evaluate the different contributions of both central and peripheral nervous factors in affecting the sensorimotor integration process in diabetes. Study I. The aim was to assess how optic flow processing contributes to the control of posture and whether it requires the predominant activation of cortical networks involved in motion perception or the intervention of subcortical loops. People with retinopathy and people who had undergone laser treatment showed a higher postural instability compared to control subjects. Differing retinal functionality produced different postural strategies. Based on these findings, postural control seems to be a process dependent on perceptual analysis via feed-forward cortical circuits. Study II. The aim was to assess whether diabetes was associated with alterations of visual gaze behaviour and/or neuromuscular impairment that might adversely affect driving performance. The potential for impaired driving performance with diabetes seems to be represented by diminished eye-steering coordination. While proprioception function seems to indicate the potential for improvement, a slower production of strength in the plantar flexor muscles seems not to influence accelerator pedal control during a driving simulation task in people with diabetes (with and without diabetic peripheral neuropathy). These results confirm the role of visual perception and eye movements in guiding human movements during dailylife activities. In particular, we demonstrated the detrimental effects of diabetes and the different contribution of diabetic retinopathy and diabetic peripheral neuropathy in affecting both central and peripheral components of the sensorimotor integration process