Retinal eccentricity of fusion detail affects vergence adaptation

Stereopsis From a Performance Perspective

PURPOSE

A patient can demonstrate a poor stereoscopic test or task performance for reasons inherent within the test/task itself for reasons dependent on normal physiology common to all human subjects, and also for reasons that are outside of normal physiology and are unique or idiosyncratic to a particular person's visual system. This article reviews the literature for the first two reasons, but emphasizes the pathophysiology involved in the idiosyncratic and abnormal reasons.

RESULTS

Using control systems analysis, it is shown that deficits in stereoscopic performance can be explained by reference to the quantitative aspect of stereoscopic threshold and qualitative aspects such as speed of response, reliability-robustness, and strength of percept. The relationship between fixation disparity and stereopsis is seen to be central to this explanation.

CONCLUSIONS

Proceeding from diagnosis to treatment, control systems analysis offers physiologically based explanations for the corrective procedures necessary to ameliorate abnormal conditions. Several topics for applied research in stereopsis are suggested.

Model-based analysis of dynamics in vergence adaptation

We previously proposed a model to study the dynamics of disparity vergence responses. This model was based on known physiology and consisted of pulse and step neural control processes feeding a linear second-order oculomotor plant. Here, we apply a slightly modified version of that model to analyze the influence of short-term adaptation on vergence dynamics. This analysis showed that, unlike normal vergence responses, adapted responses could not be accurately simulated without a delay between the step and pulse components. Through simulations of normal vergence and adapted vergence responses, we found a strong correlation between delay of the step signal and the size of the movement overshoot. This correlation suggests a strong interaction between neural process generating the pulse and step motor control signals.