Proximal contribution to a linear static model of accommodation and vergence

Area of Science:

• Ophthalmology and Vision Science
• Biomedical Engineering
• Human Factors and Ergonomics

Background:

• Accommodation and vergence are crucial for clear and single binocular vision.
• Understanding the influence of target proximity on these visual responses is essential.
• Previous models have explored dual-interactive feedback but lacked detailed analysis of proximal inputs under varying conditions.

Purpose of the Study:

• To quantify the impact of target proximity on accommodation and vergence.
• To investigate these effects under both open-loop (OL) and closed-loop (CL) viewing conditions.
• To analyze the role of proximal accommodation (PA) and proximal vergence (PV) within a feedback model.

Main Methods:

• Developed and quantitatively analyzed a static interactive feedback model incorporating PA and PV inputs.
• The model was based on an existing static dual-interactive feedback model.
• Proximal inputs were integrated into the accommodative and vergence control loops; PA and PV gains were derived from experimental dual-OL data.

Main Results:

• Under dual-OL conditions, PA contributed 42.5–81.6% to accommodation, and PV contributed 56.1–88.5% to vergence.
• In contrast, under most CL conditions, these contributions were significantly smaller (0.04–7.0%).
• Specifically, under dual-CL (normal viewing), PA and PV contributions were only 4.0% and 0.04%, respectively.

Conclusions:

• Proximal accommodation and vergence play a substantial role in open-loop viewing but minimal role in closed-loop viewing.
• Despite small contributions in CL conditions, proximity cues remain important for achieving coordinated motor responses in natural viewing.
• The findings highlight the differential impact of proximal feedback depending on the visual feedback loop's integrity.