We recently proposed a method that allows dichoptic visual stimulus presentation and binocular eye tracking simultaneously1. The key is the combination of an infrared eye tracker and the corresponding infrared-transparent mirrors. This manuscript provides an in depth protocol for initial setup and everyday operation.
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Method Article
How to Build a Dichoptic Presentation System That Includes an Eye Tracker
In This Article
Summary
Abstract
The presentation of different stimuli to the two eyes, dichoptic presentation, is essential for studies involving 3D vision and interocular suppression. There is a growing literature on the unique experimental value of pupillary and oculomotor measures, especially for research on interocular suppression. Although obtaining eye-tracking measures would thus benefit studies that use dichoptic presentation, the hardware essential for dichoptic presentation (e.g. mirrors) often interferes with high-quality eye tracking, especially when using a video-based eye tracker. We recently described an experimental setup that combines a standard dichoptic presentation system with an infrared eye tracker by using infrared-transparent mirrors1. The setup is compatible with standard monitors and eye trackers, easy to implement, and affordable (on the order of US$1,000). Relative to existing methods it has the benefits of not requiring special equipment and posing few limits on the nature and quality of the visual stimulus. Here we provide a visual guide to the construction and use of our setup.
Introduction
Under normal viewing conditions each of our eyes receives a slightly different visual input. This input is then processed to produce one coherent, three-dimensional representation of the world. Dichoptic presentation, the practice of independently controlling the input presented to each of the two eyes, thus enables researchers to study how humans reconstruct a three-dimensional representation from two two-dimensional retinal images2,3,4. In addition, if the two eyes' images are too dissimilar, this interocular combination fails, and observers instead report perception of....
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Protocol
This protocol has been approved by the Institutional Review Boards of Michigan State University.
1. Building the system
- Rationale
- Prepare the mirror setup, a variant of the classic Wheatstone stereoscope28 illustrated in Figure 1, consisting of two mirrors positioned at a 45° angle relative to the participant's midline. The mirrors reflect stimuli from two screens that are positioned at opposite ends of a table, facing each other.
- Seat a participant in front of the mirrors and have them view a different screen, reflected via a ....
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Results
After the calibration described in the protocol, we performed a calibration-validation procedure without problems with the mirrors in place. The effectiveness of the method is clearly illustrated by Figure 5, which shows the camera's image (using a research end eye tracking system) with the mirrors in place. The two sets of parallel lines along participants' nose and the lines above the eye brows are the edges of the mirrors but, nevertheless, the face is as .......
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Discussion
We present a step-by-step guide for the construction and use of an experimental setup that allows simultaneous tracking of the both eyes and dichoptic presentation of visual stimuli. In many situations where dichoptic stimulation is used, the critical issue preventing effective eye tracking is that the mirrors for dichoptic presentation block the sight of video-based eye trackers. This is resolved here by using infrared-transparent mirrors and an infrared-sensitive eye tracker. This setup allows researchers of 3D vision,.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors thank Pieter Schiphorst for his role in designing the setup and for providing the graphics of Figures 1 and 3, and Marnix Naber for helpful discussion and his contribution to Figure 6. The authors also acknowledge researchers and publishers for reusing Figure 1 and 6 from a published paper1.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Mirrors in Setup 1 | Edmund Optics | #64-452 | dimensions 10.10 × 12.70 cm; Reflectance: 400 ~ 690 nm; Transmission: 750 ~ 1200nm |
| Mirrors in Setup 2 | Edmund Optics | Item discontinued | dimensions 10.10 × 12.70 cm; Reflectance: 425 ~ 650 nm; Transmission: 800 ~ 1200nm |
| Other Mirror Option | Edmund Optics | #62-634 | dimensions 12.50 × 12.50 cm; Reflectance: 425 ~ 650 nm; Transmission: 800 ~ 1200nm |
| Eye Tracker in Setup 1 | SR Research Ltd., Mississauga, Ontario, Canada | Eyelink 1000 | Transmission: 890 ~ 940 nm |
| Eye Tracker in Setup 2 | The Eye Tribe Aps, Copenhagen, Denmark | Eye Tribe (item discontinued) | Transmission: around 850 nm |
References
- Brascamp, J. W., Naber, M. Eye tracking under dichoptic viewing conditions: a practical solution. Behav. Res. Methods. , 1-7 (2016).
- Barendregt, M., Harvey, B. M., Rokers, B., Dumoulin, S. O. Transformation from a Retinal to a Cyclopean Representation in Human Visual Cortex.<....
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