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.

This protocol has been approved by the Institutional Review Boards of Michigan State University.
1. Building the system
<ol>
	<li>Rationale
	<ol>
		<li>Prepare the mirror setup, a variant of the classic Wheatstone stereoscope28 illustrated in Figure 1, consisting of two mirrors positioned at a 45&#176; angle relative to the participant&#39;s midline. The mirrors reflect stimuli from two screens that are positioned at oppo...

<ol>
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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,...

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&#39; images are too dissimilar, this interocular combination fails, and observers instead report perception of only one of the images at a time while the other remains suppressed, in phenomena such as binocular rivalry5 and continuous flash suppression6. Researchers of such interocular suppression, too, use dichoptic presentation, in this case to examine questions related to topics like the neural locus of awareness7, perceptual selection8,9, and unconscious processing10.
Gaze and pupil dynamics are recorded for multiple purposes in research on human behavior and perception. Gaze direction can inform about, for instance, attention allocation11,10,13 and decision making14, while pupil size can reveal aspects of visual processing15,16, task engagement17, or fluid intelligence18.
Combining eye tracking with dichoptic presentation is useful in research into, for instance, three dimensional (3D) perception19,20,21,22 or ocular responses to visual input during interocular suppression23,24,25. For example, eye movements have been found to reveal unconscious processing without subjective perception during continuous flash suppression23. Clinical visual researchers can use the ability to track both eyes during dichoptic presentation to investigate ocular diseases that affect the two eyes asymmetrically, for example, to monitor the monocular and binocular visual distortions occurring in amblyopia26 and maculopathy27.
We recently described a setup1 that allows for the combination of high quality video-based eye tracking and dichoptic stimulation with little limitation on the size or color of the stimuli, and we evaluated its performance. Below we will summarize the construction and use of this setup.

<table border="0" cellpadding="0" cellspacing="0" width="1130">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:163px;">Mirrors in Setup 1</td>
			<td style="width:283px;">Edmund Optics</td>
			<td style="width:169px;">&#160;#64-452</td>
			<td style="width:516px;">dimensions 10.10 &#215; 12.70 cm; Reflectance: 400 ~ 690 nm; Transmission: 750 ~ 1200nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:163px;">Mirrors in Setup 2</td>
			<td style="width:283px;">Edmund Optics</td>
			<td style="width:169px;">Item discontinued</td>
			<td>dimensions 10.10 &#215; 12.70 cm; Reflectance: 425 ~ 650 nm; Transmission: 800 ~ 1200nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Other Mirror Option</td>
			<td style="width:283px;">Edmund Optics</td>
			<td>#62-634</td>
			<td>dimensions 12.50 &#215; 12.50 cm; Reflectance: 425 ~ 650 nm; Transmission: 800 ~ 1200nm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:163px;">Eye Tracker in Setup 1</td>
			<td style="width:283px;">SR Research Ltd., Mississauga, Ontario, Canada</td>
			<td style="width:169px;">Eyelink 1000</td>
			<td>Transmission: 890 ~ 940 nm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:163px;">Eye Tracker in Setup 2</td>
			<td style="width:283px;">The Eye Tribe Aps, Copenhagen, Denmark</td>
			<td style="width:169px;">Eye Tribe (item discontinued)</td>
			<td>Transmission: around 850 nm</td>
		</tr>
	</tbody>
</table>

how to build a dichoptic presentation system that includes an eye tracker

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.

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&#39;s image (using a research end eye tracking system) with the mirrors in place. The two sets of parallel lines along participants&#39; nose and the lines above the eye brows are the edges of the mirrors but, nevertheless, the fac...

Watch this Scientific Journal Video about How to Build a Dichoptic Presentation System That Includes an Eye Tracker at JoVE.com

How to Build a Dichoptic Presentation System That Includes an Eye Tracker

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.

The presentation of different stimuli to the two eyes, dichoptic presentation, is essential for studies involving 3D vision and interocular suppression. ...

The overall goal of this procedure is to achieve binocular eye tracking during dichoptic visual stimulus presentation. In the study of vision, it's often important to show each eye, a different image. For instance, using mirrors.This is called, dichoptic stimulation. The main advantage of this technique is that it allows eye tracking during dichoptic viewing in a set up that is very compatible with standard eye trackers and has low cost and poses very few limits on the size and color of the visual stimuli you use. This method can help answer key questions in the study of human vision, like, how do the eyes move in 3D scenes and how do the pupils respond to visual input that's presented subconsciously using a technique called, interocular suppression.Generally, individuals attempting to do eye tracking in normal dichoptic set ups will struggle because the mirrors used for dichoptic presentation, block the sight of video based eye trackers. To build the fiberboard framework, begin by putting together one central component, which will hold the mirrors and eye tracker and two reference boards painted in matte black to reduce light scatter. Place the top element of this component, such that it leaves eight centimeters in depth in front of the desk, to allow enough room for the participant's face when stabilized on the headrest and avoid condensation on the mirrors during exploration.Next, position the two reference boards at the desired locations of the monitors. Mount two flat screen monitors on standard monitor arms, clamped to the side of the desk to allow translation in three dimensions, as well as rotation in the plane of the screen. Then, connect the mirror mounts to the fiberboard and stabilize the mirrors on the mirror mounts.Position the mirrors to touch at a 90 degree angle in the center, in order to reflect stimuli from the two screens that are positioned at opposite ends of the table. Align the headrest with the center of mirrors. Finally, create blinders made of black cardboard and foam padded whole straps painted in black and attach them to the posts of the headrest.Position the eye tracker behind the mirrors and the whole set up is ready for experiments. Begin by seating a participant in front of the mirrors and have them view a different screen reflected via a different mirror with each eye. For best results, use a headrest for stabilizing the participant's head.Position an infrared sensitive video based eye tracker, including a camera and an illuminator in front of the participant but behind the mirrors. If the desired monitor position is lost, retrieve this position by using the markings on the calibration board, to put the board back in the same place, relative to the reference board that has a fixed position on the desk. Move the monitor again to line up with the appropriate markings.When using blinders, move them to the participant's eye level and rotate them slightly toward the midline to minimize participant's exposure to other visual input. Ensure that each eye can see the whole visual stimulus in the mirror without seeing any of it directly. For the software calibration, present a dot on each of the two screens in alternation.Instruct the participant to eliminate the perceived position change, by moving the dot on one of the screens. Alternatively, instruct the participant to align the frames of experimental stimuli instead of two dots, so that both visual fields critical to the particular experiment are aligned. Finally, after applying either method, center the stimuli in the experiment on the resulting onscreen positions to begin the experiment.During the experiment, the image shown in the eye tracker software will just look as if the mirrors are not there. A short experiment was conducted with only one mirror in place to compare the results with and without the mirror. The participant made to different locations on the screen with one eye tracked without the mirror and the other eye tracked with the mirror.The eye tracker did not miss any samples for either eye. The average correlations in the horizontal gaze angle and vertical gaze angle were 0.99. While building this set up, it is important to purchase code mirrors that feature near complete reflectance of visible wavelength and near complete transmission of near infrared wavelength.Once mastered, this set up and calibration can be completed in 10 minutes for each participant if performed properly. After watching this video, you should have a good understanding of how to build and use this dichoptic presentation system with an eye tracker. After this development, this technique paved the way for researchers in the field of vision science to explore a gaze and pupil dynamics with a system that allows dichoptic visual presentation.

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8.3K visualizações.  Michigan State University. The overall goal of this procedure is to achieve binocular eye tracking during dichoptic visual stimulus presentation. In the study of vision, it's often important to show each eye, a different image. For instance, using mirrors.This is called, dichoptic stimulation. The main advantage of this technique is that it allows eye tracking during dichoptic viewing in a set up that is very compatible with standard eye trackers and has low cost and poses very few limits on the size and color o...