This research was funded by LC Industries Postdoctoral research fellowship to RR and Bosma Enterprises Postdoctoral research fellowship to AK. The authors would like to thank Drs. Laura Walker and Donald Fletcher for their valuable suggestions and help in subject recruitment.

All the procedures and protocol described below were reviewed and approved by the institutional review board of Wichita State University, Wichita, Kansas. Informed consent was obtained from all the participants.
1. Participant selection
<ol>
	<li>Recruited participants with normal vision (n=5, 4 females, mean &#177; SE: 39.8 &#177; 2.6 years), and with central vision loss (n=15, 11 females, 78.3 &#177; 2.3 years) due to macular degeneration (age-related/juvenile). Note that grossly different ages of the two groups was secondary to demographics of the subjects with central vision loss (age-related macular degeneration affects older subjects and is more prevalent in females). Further, the goal of this study was not comparing the two cohorts.</li>
</ol>
2. Preparation of the experiment
<ol>
	<li>Use a wireless 3D active shutter glasses (Table of Materials) that can be synced with any 3D-ready monitor. For the shutter glasses to be active, there should be no interference between the infrared transmitter (a small pyramid-shaped black box) and the infrared receiver (sensor) on the nose bridge of the shutter glasses.</li>
	<li>Display all the visual stimuli on a 3D monitor (1920 x 1080 pixels, 144 Hz). For the monitor and the 3D glasses to work seamlessly, ensure that appropriate drivers are installed.</li>
	<li>Use a table-mounted infrared video-based eye-tracker (Table of Materials) that is capable of measuring eye movements at the sampling of 1000 Hz for this protocol. Separate the infrared illumination and camera of the eye-tracker use any tripod with adjustable height and angle (Table of Materials) to hold them firmly in place. Place the camera at a distance of 20-30 cm from the participant and place the screen at a distance of 100 cm from the participant.</li>
	<li>Use an infrared reflective patch (Table of Materials) to avoid the interference between infrared illumination of the eye-tracker and the infrared system of the shutter glasses (Figure 1, Right).</li>
	<li>Use commercially available software (Table of Materials) to integrate shutter glasses and 3D ready monitor for dichoptic presentation of visual stimuli to control the eyetracker.</li>
	<li>To stabilize the head movements, use a tall and wide chin and forehead rest (Table of Materials) and clamp it to an adjustable table. The wide dimension of the chin and forehead rest allows&#160;comfortable positioning of participants with the shutter glasses on. 
	NOTE: Figure 1 shows the setup for eye-tracking with dichoptic stimulus presentation using 3D shutter glasses and 3D-ready monitor. The infrared reflective patch was strategically placed below the infrared sensor on the nose bridge of 3D shutter glasses (Figure 1, Right).</li>
	<li>Minimize the leakage of luminance information by deactivating the light-boost option in the 3D ready monitor. The leakage of luminance information from one eye to the other eye is known as luminance leakage or crosstalk13. This is prone to occur&#160;with the stereoscopic displays in the high luminance conditions.</li>
	<li>Because of the shutters, the amount of infrared illumination (from the eye-tracking system) reaching the pupil can be significantly reduced13 &#8211; on an average, approximately 65% of luminance was reduced (Supplementary Table 1). To overcome this, increase the strength of the infrared LEDs of the eyetracker to 100% or (the maximum setting) from the default power setting. When using the infrared video-based eye-tracker (Table of Materials) change this setting in the &#8220;Illumination power&#8221; settings in the left bottom screen as shown in Figure 2.</li>
</ol>
3. Running the experiment
NOTE: The main experiment of this study was binocular eye tracking and screening of the central visual field using dichoptic stimulus. The central visual field screening was comparable to the visual field testing of commercially available instruments (Table of Materials). The physical properties of the visual stimulus such as luminance of the target (~22 cd/m2), luminance of the background (~10 cd/m2), size of the target (Goldmann III &#8211; 4 mm2), the visual field grid (Polar 3 grid with 28 points, Figure 3), and stimulus duration (200 ms) were identical to the visual field testing of commercially available instruments. Note that these luminance values were measured through shutter glasses when the shutter was ON (Supplementary Table 1). For the purposes of testing discussed here, the luminance of the stimulus was constant unlike visual field testing where the luminance of the stimulus is altered to obtain a detection threshold. In other words, the experiment employed supra-threshold screening and not thresholding. Therefore, the results of the screening were binary responses (stimuli seen or not seen) and not numerical values.
<ol>
	<li>Pre-experiment checks
	<ol>
		<li>A couple of minutes before the participant arrives for the testing, ensure that both eye tracker and the host computer (that runs the experiment) is turned on and confirm that the host computer is connected to the eyetracker.</li>
		<li>As a rule, confirm the synchronization accuracy (using platform specific commands) of the display before beginning the experiment.</li>
	</ol>
	</li>
	<li>Initiating the main experiment 
	NOTE:&#160;The steps below are very platform specific and is contingent on the script that runs the main experiment. See Supplementary Material&#160;that contain the samples of the codes used to design and run the experiment.
	<ol>
		<li>Initiate the program (See Supplementary Material - &#8216;ELScreeningBLR.m&#8217;) that runs the main experiment from the appropriate interface. When and if prompted by the program, enter the participant information (such as participant ID, test distance) that is needed to save the output data file in the data folder with a unique filename.</li>
		<li>A gray screen with instructions such as &#8220;Press Enter to toggle camera; Press C to calibrate, Press V to validate&#8221; will appear on the screen. At this stage, adjust the camera of the eye-tracker to align with the participant&#8217;s pupil as shown in Figure 2.</li>
	</ol>
	</li>
	<li>Eye-tracker calibration and validation
	<ol>
		<li>Initiate the calibration of the eye-tracker. Instruct the participants to follow the target by moving the eyes (and not head) and look at the center of the target.</li>
		<li>After the successful calibration, initiate the validation. Provide the same instructions as the calibration.</li>
		<li>Read the results of the validation step (usually displayed on the screen). Repeat the calibration and validation until &#8220;good/fair&#8221; (as recommended by the eyetracker manual) result is obtained.</li>
	</ol>
	</li>
	<li>Drift correction
	<ol>
		<li>Once the calibration and validation of the eye-tracker is done, initiate the drift correction.</li>
		<li>Instruct the participants to &#8220;look at the central fixation target and hold their eyes as steady as possible&#8221;. 
		NOTE: After the calibration, validation, and drift correction, the eye-tracking will be initiated simultaneously with the main experiment.</li>
	</ol>
	</li>
	<li>Visual field screening
	<ol>
		<li>Re-instruct/remind the participant about the task that he/she must do during the experiment. Ask subjects to keep both eyes open during the entire testing.</li>
		<li>For this visual field experiment, instruct them to hold the fixation at the central fixation target while responding to &#8220;any white light seen&#8221; by pressing the &#8220;enter&#8221; button in the response button (Figure 1, Table of Materials). Instruct them not to move the eyes and search for the new white lights. Also, remind them that the brief white lights can appear at any location on the screen. 
		NOTE: During visual field screening, the functioning of shutter glasses can be probed using monocular targets that can be fused to form a complete percept (See Supplementary Figure 2 &#8211; catch trials).</li>
		<li>Re-iterate the instruction to &#8220;hold fixation&#8221; several times throughout the experiment to ensure the fixation falls within the desired area. 
		NOTE: An audio feedback (like an error tone) can be used to alert loss of fixation (like eyes moved outside a tolerance window). When fixation lapses, reinstruct the participant to fixate only on the cross target. The visual stimuli presentation can be temporarily stopped until the participant brings the fixation back within the tolerance window (like central 2&#176;).</li>
		<li>At the end of the visual field experiment, the screen will display the result of the testing highlighting the seen and non-seen locations differently (like for example Figure 6).</li>
	</ol>
	</li>
	<li>Saving the data file
	<ol>
		<li>All the visual field data (say saved as &#8220;. mat&#8221; file) and eye-movement data (say saved as &#8220;.edf&#8221; file) will be saved automatically for post-hoc analysis. However, ensure that the files have been saved before quitting the program/platform running the experiment.</li>
	</ol>
	</li>
</ol>
4. Analysis
NOTE: The analysis of eye movement and visual field data can be performed in several ways and is contingent on the software used to run the experiment and data format of eye tracker&#8217;s output. The steps below are specific to the setup and the program (See Supplementary Materials).
<ol>
	<li>Eye movement analysis (post-hoc) 
	NOTE: The saved eye movements data file (EDF) is a highly compressed binary format, and it contains many types of data, including eye movement events, messages, button presses, and gaze position samples.
	<ol>
		<li>Convert EDF to ASC-II files using a translator program (EDF2ASC).</li>
		<li>Run &#8216;PipelineEyeMovementAnalysisERI.m&#8217; to initialize eye movement analysis and follow the instructions as noted in the code (See Supplementary Materials for the code script).</li>
		<li>Run &#8216;EM_plots.m&#8217;, to extract horizontal and vertical eye positions and to plot as shown in Figure 4 and Figure 5. 
		NOTE: Eye movement data can be further analyzed to compute fixation stability, detect microsaccades, etc. However, this is beyond the scope of the current paper.</li>
	</ol>
	</li>
	<li>Visual fields
	<ol>
		<li>To get the reports of visual field test, run &#8216;VF_plot.m&#8217;. 
		NOTE: All datasets pertaining to the visual field experiment such as points seen/not seen will be plotted as a visual field map as shown in Figure 6. If a point was seen, then it will be plotted as &#8220;green&#8221; filled square, otherwise a red filled square will be plotted. No post-hoc analysis for visual field data will be required.</li>
	</ol>
	</li>
</ol>

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	<li>Fletcher, D. C., Schuchard, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preferred+retinal+loci+relationship+to+macular+scotomas+in+a+low-vision+population.">Preferred retinal loci relationship to macular scotomas in a low-vision population.</a> Ophthalmology. 104 (4), 632-638 (1997).</li><li>Raveendran, R. N., Babu, R. J., Hess, R. F., Bobier, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+improvements+in+fixational+stability+in+strabismic+amblyopes+following+bifoveal+fixation+and+reduced+interocular+suppression.">Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.</a> Ophthalmic &amp; Physiological Optics. 34, 214-225 (2014).</li><li>Nystr&#246;m, M., Hansen, D. W., Andersson, R., Hooge, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+have+microsaccades+become+larger?+Investigating+eye+deformations+and+detection+algorithms.">Why have microsaccades become larger? Investigating eye deformations and detection algorithms.</a> Vision Research. , (2014).</li><li>Raveendran, R. N., Babu, R. J., Hess, R. F., Bobier, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+improvements+in+fixational+stability+in+strabismic+amblyopes+following+bifoveal+fixation+and+reduced+interocular+suppression.">Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.</a> Ophthalmic and Physiological Optics. 34 (2), (2014).</li><li>Brascamp, J. W., Naber, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Eye+tracking+under+dichoptic+viewing+conditions:+a+practical+solution.">Eye tracking under dichoptic viewing conditions: a practical solution.</a> Behavior Research Methods. 49 (4), 1303-1309 (2017).</li><li>Qian, C. S., Brascamp, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+build+a+dichoptic+presentation+system+that+includes+an+eye+tracker.">How to build a dichoptic presentation system that includes an eye tracker.</a> Journal of Visualized Experiments. (127), (2017).</li><li>Raveendran, R. N., Bobier, W. R., Thompson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binocular+vision+and+fixational+eye+movements.">Binocular vision and fixational eye movements.</a> Journal of Vision. 19 (4), 1-15 (2019).</li><li>. Binocular vision and fixational eye movements Available from: <a target="_blank" href="https://uwspace.uwaterloo.ca/handle/10112/12076">https://uwspace.uwaterloo.ca/handle/10112/12076</a> (2017)</li><li>. Fixational eye movements in strabismic amblyopia Available from: <a target="_blank" href="https://uwspace.uwaterloo.ca/handle/10012/7478">https://uwspace.uwaterloo.ca/handle/10012/7478</a> (2013)</li><li>Maiello, G., Chessa, M., Solari, F., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simulated+disparity+and+peripheral+blur+interact+during+binocular+fusion.">Simulated disparity and peripheral blur interact during binocular fusion.</a> Journal of Vision. 14 (8), (2014).</li><li>Maiello, G., Harrison, W. J., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monocular+and+binocular+contributions+to+oculomotor+plasticity.">Monocular and binocular contributions to oculomotor plasticity.</a> Scientific Reports. 6, (2016).</li><li>Maiello, G., Kwon, M. Y., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+binocular+eye-hand+coordination+in+normal+vision+and+with+simulated+visual+impairment.">Three-dimensional binocular eye-hand coordination in normal vision and with simulated visual impairment.</a> Experimental Brain Research. 236 (3), 691-709 (2018).</li><li>Agaoglu, S., Agaoglu, M. N., Das, V. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motion+Information+via+the+Nonfixating+Eye+Can+Drive+Optokinetic+Nystagmus+in+Strabismus.">Motion Information via the Nonfixating Eye Can Drive Optokinetic Nystagmus in Strabismus.</a> Investigative Opthalmology &amp; Visual Science. 56 (11), 6423 (2015).</li><li>Erkelens, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fusional+limits+for+a+large+random-dot+stereogram.">Fusional limits for a large random-dot stereogram.</a> Vision Research. 28 (2), 345-353 (1988).</li><li>Seiple, W., Szlyk, J. P., McMahon, T., Pulido, J., Fishman, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Eye-movement+training+for+reading+in+patients+with+age-related+macular+degeneration.">Eye-movement training for reading in patients with age-related macular degeneration.</a> Investigative Ophthalmology and Visual Science. 46 (8), 2886-2896 (2005).</li><li>Aguilar, C., Castet, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gaze-contingent+simulation+of+retinopathy:+Some+potential+pitfalls+and+remedies.">Gaze-contingent simulation of retinopathy: Some potential pitfalls and remedies.</a> Vision Research. 51 (9), 997-1012 (2011).</li><li>Pratt, J. D., Stevenson, S. B., Bedell, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scotoma+Visibility+and+Reading+Rate+with+Bilateral+Central+Scotomas.">Scotoma Visibility and Reading Rate with Bilateral Central Scotomas.</a> Optom Vis Sci. 94 (31), 279-289 (2017).</li><li>Babu, R. J., Clavagnier, S., Bobier, W. R., Thompson, B., Hess, R. F., PGH, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regional+Extent+of+Peripheral+Suppression+in+Amblyopia.">Regional Extent of Peripheral Suppression in Amblyopia.</a> Investigative Opthalmology &amp; Visual Science. 58 (4), 2329 (2017).</li><li>Ebenholtz, S. 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The authors have nothing to disclose. Parts of the study presented here were presented as abstract titled &#8220;Binocular Central Visual Function in Macular Degeneration&#8221; in the annual meeting of American academy of Optometry 2019.

The proposed method of measuring eye movements in dichoptic viewing condition has many potential applications. Assessing binocular visual fields in participants with central vision loss that is demonstrated here is one such application. We used this method to assess binocular visual field in fifteen participants with central vision loss to study how binocular viewing influences the heterogeneous central visual field loss.
The most important step in the protocol is positioning (distance from ey...

Macular degeneration is generally a bilateral condition affecting central vision and the pattern of visual loss can be heterogeneous. The central visual loss could be either symmetrical or asymmetrical between two eyes1. Currently, there are several techniques available to assess the central visual field in macular degeneration. The Amsler grid chart contains a grid pattern that can be used to manually screen central visual field. Automated perimeters (e.g., Humphrey visual field analyzer) present light flashes of varying brightness and sizes in a standardized ganzfeld bowl to probe the visual field. Gaze-contingent microperimetry presents visual stimulus on an LCD display. Micro-perimeters can compensate micro-eye movements by tracking a region of interest on the retina. Micro-perimeters can probe local regions in the central retina for changes in function but can test only one eye at a time. Consequently, micro-perimetric testing cannot explain how the heterogeneous defects in each eye affect the binocular interaction and real-world function. There is an unmet need for a method to reliably assess visual fields in a viewing condition that closely approximates real-world viewing. Such an assessment is necessary to understand how the visual field defect of one eye affects/contributes to the binocular visual field defect. We propose a novel method for assessing central visual field in people with central visual loss under dichoptic viewing condition (i.e., when visual stimuli are independently presented to each of the two eyes).
To measure visual fields reliably, fixation must be maintained at a given locus. Therefore, it is important to combine the eye-tracking and dichoptic presentation for binocular assessment. However, combining these two techniques can be challenging due to interference between the illuminating systems of the eye-tracker (e.g., infrared LEDs) and the optical elements of the dichoptic presenting systems (e.g., mirrors of haploscope or prisms of stereoscopes). Alternative options are to use an eye-tracking technique that does not interfere with the line of sight (e.g., scleral coil technique) or an eye-tracker that is integrated with goggles2. Though each method has its own benefits, there are disadvantages. The former method is considered invasive and can cause considerable discomfort3 and the latter methods have low temporal resolutions (60 Hz)4. To overcome these issues, Brascamp &#38; Naber (2017)5 and Qian &#38; Brascamp (2017)6 used a pair of cold mirrors (which transmitted infrared light but reflected 95% of the visible light) and a pair of monitors on either side of the cold mirrors to create a dichoptic presentation. Infrared video-based eye-tracker was used to track eye movements in the haploscope setup7,8.
However, using a haploscope-type dichoptic presentation has a drawback. The center of rotation of the instrument (haploscope) is different from the center of rotation of the eye. Therefore, additional calculations (as described in Appendix &#8211; A of Raveendran (2013)9) are required for proper and accurate measurements of eye movements. In addition, the planes of accommodation and vergence must be aligned (i.e., demand for accommodation and vergence must be the same). For example, if the working distance (total optical distance) is 40 cm, then the demand for accommodation and vergence is 2.5 diopters and 2.5-meter angles, respectively. If we align the mirrors perfectly orthogonal, then the haploscope is aligned for distant viewing (i.e., required vergence is zero), but the required accommodation is still 2.5D. Therefore, a pair of convex lenses (+2.50 diopters) must be placed between the eye and mirror arrangement of haploscope to push the plane of accommodation to infinity (i.e., required accommodation is zero). This arrangement necessitates more space between the eye and mirror arrangement of haploscope is required, which takes us back to the difference in centers of rotation. The issue of aligning planes of accommodation and vergence can be minimized by aligning the haploscope to the near viewing such that both the planes are aligned. However, this requires measurement of inter-pupillary distance for every participant and the corresponding alignment of haploscope mirrors/stimulus presenting monitors.
In this paper, we introduce a method to combine infrared video-based eye-tracking and dichoptic stimulus presentation using wireless 3D shutter glasses and 3D-ready monitors. This method does not require any additional calculations and/or assumptions like those used with the haploscopic method. Shutter glasses have been used in conjunction with eye trackers for understanding binocular fusion10, saccadic adaptation11, and eye-hand coordination12. However, it should be noted that stereo-shutter glasses used by Maiello and colleagues10,11,12 were the first-generation shutter glasses, which were connected through a wire to synchronize with the monitor refresh rate. Moreover, the first-generation shutter glasses are commercially unavailable now. Here, we demonstrate the use of commercially available second-generation wireless shutter glasses (Table of Materials) to present dichoptic stimulus and reliably measure monocular and binocular eye-movements. Additionally, we demonstrate a method to assess monocular/binocular visual fields in subjects with central visual field loss. While dichoptic presentation of visual stimulus enables monocular and binocular assessment of visual fields, binocular eye tracking under dichoptic viewing condition facilitates visual fields testing in a gaze-controlled paradigm.

<table>
	<tbody>
		<tr>
			<td>3D monitor</td>
			<td>Benq</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 500 
			https://zowie.benq.com/en/product/monitor/xl/xl2720.html</td>
		</tr>
		<tr>
			<td>3D shutter glass</td>
			<td>NVIDIA</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 300 
			https://www.nvidia.com/object/product-geforce-3d-vision2-wireless-glasses-kit-us.html</td>
		</tr>
		<tr>
			<td>Chin/forehead rest</td>
			<td>UHCO</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 750 
			https://www.opt.uh.edu/research-at-uhco/uhcotech/headspot/</td>
		</tr>
		<tr>
			<td>Eyetracker</td>
			<td>SR Research</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 27,000 
			https://www.sr-research.com/eyelink-1000-plus/</td>
		</tr>
		<tr>
			<td>IR reflective patch</td>
			<td>Tactical</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 10 
			https://www.empiretactical.org/infrared-reflective-patches/tactical-infrared-ir-square-patch-with-velcro-hook-fastener-1-inch-x-1-inch</td>
		</tr>
		<tr>
			<td>MATLAB Software</td>
			<td>Mathworks</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 2150 
			https://www.mathworks.com/pricing-licensing.html</td>
		</tr>
		<tr>
			<td>Numerical Keypad</td>
			<td>Amazon</td>
			<td>CP001878 (model), B01E8TTWZ2 (ASIN)</td>
			<td>Approximate Cost (in USD): 15 
			https://www.amazon.com/Numeric-Jelly-Comb-Portable-Computer/dp/B01E8TTWZ2</td>
		</tr>
		<tr>
			<td>Psychtoolbox - Add on</td>
			<td>Freeware</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): FREE 
			http://psychtoolbox.org/download.html</td>
		</tr>
		<tr>
			<td>Tripod (Dekstop)</td>
			<td>Manfrotto</td>
			<td>MTPIXI-B (model), B00D76RNLS (ASIN)</td>
			<td>Approximate Cost (in USD): 30 
			https://www.amazon.com/dp/B00D76RNLS</td>
		</tr>
	</tbody>
</table>

assessing binocular central visual field and binocular eye movements in a dichoptic viewing condition

Macular degeneration typically results in heterogeneous binocular central visual defects. Currently available approaches to assess central visual field, like the microperimetry, can test only one eye at a time. Therefore, they cannot explain how the defects in each eye affect the binocular interaction and real-world function. Dichoptic stimulus presentation with a gaze-controlled system could provide a reliable measure of monocular/binocular visual fields. However, dichoptic stimulus presentation and simultaneous eye-tracking are challenging because optical devices of instruments that present stimulus dichoptically (e.g., haploscope) always interfere with eye-trackers (e.g., infrared video-based eye-trackers). Therefore, the goals were 1) to develop a method for dichoptic stimulus presentation with simultaneous eye-tracking, using 3D-shutter glasses and 3D-ready monitors, that is not affected by interference and 2) to use this method to develop a protocol for assessing central visual field in subjects with central vision loss. The results showed that this setup provides a practical solution for reliably measuring eye-movements in dichoptic viewing condition. In addition, it was also demonstrated that this method can assess gaze-controlled binocular central visual field in subjects with central vision loss.

The representative binocular eye-movement traces of one observer with normal binocular vision during two different viewing conditions is shown (Figure 4). Continuous tracking of eye movements was possible when both eyes viewed the stimulus (Figure 4A), and when the left eye viewed the stimulus with the right eye under an active shutter (Figure 4B). As evident from these traces, the proposed method does not impact the quality of eye-...

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Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition

Presented here is a protocol for assessing binocular eye movements and gaze-controlled central visual field screening in participants with central vision loss.

Macular degeneration typically results in heterogeneous binocular central visual defects. Currently available approaches to assess central visual field, ...

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4.3K Views.  Envision Research Institute. Presented here is a protocol for assessing binocular eye movements and gaze-controlled central visual field screening in participants with central vision loss.

Video: Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition

Using Eye Movements to Evaluate the Cognitive Processes Involved in Text Comprehension

The present article describes how to use eye tracking methodologies to study the cognitive processes involved in text comprehension. Measuring eye movements during reading is one of the most precise methods for measuring moment-by-moment (online) processing demands during text comprehension. Cognitive processing demands are reflected by several aspects of eye movement behavior, such as fixation duration, number of fixations, and number of regressions (returning to prior parts of a text). Important properties of eye tracking equipment that researchers need to consider are described, including how frequently the eye position is measured (sampling rate), accuracy of determining eye position, how much head movement is allowed, and ease of use. Also described are properties of stimuli that influence eye movements that need to be controlled in studies of text comprehension, such as the position, frequency, and length of target words. Procedural recommendations related to preparing the participant, setting up and calibrating the equipment, and running a study are given. Representative results are presented to illustrate how data can be evaluated. Although the methodology is described in terms of reading comprehension, much of the information presented can be applied to any study in which participants read verbal stimuli.

The present article describes how to use eye tracking methodologies to study the cognitive processes involved in text comprehension. Descriptions of eye tracking equipment, how to develop experimental stimuli, and procedural recommendations are included. The information presented can be applied to most any study using verbal stimuli.

The present article describes how to use eye  tracking methodologies to study the cognitive processes involved in text  comprehension. Measuring eye ...

A Method to Quantify Visual Information Processing in Children Using Eye Tracking

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational methods, it is difficult to make a quantitative assessment of a child's visual problems. This limits accurate diagnostics in children under the age of 4 years and in children with intellectual disabilities. Here we describe a quantitative method that overcomes these problems. The method uses a remote eye tracker and a four choice preferential looking paradigm to measure eye movement responses to different visual stimuli. The child sits without head support in front of a monitor with integrated infrared cameras. In one of four monitor quadrants a visual stimulus is presented. Each stimulus has a specific visual modality with respect to the background, e.g., form, motion, contrast or color. From the reflexive eye movement responses to these specific visual modalities, output parameters such as reaction times, fixation accuracy and fixation duration are calculated to quantify a child's viewing behavior. With this approach, the quality of visual information processing can be assessed without the use of communication. By comparing results with reference values obtained in typically developing children from 0-12 years, the method provides a characterization of visual information processing in visually impaired children. The quantitative information provided by this method can be advantageous for the field of clinical visual assessment and rehabilitation in multiple ways. The parameter values provide a good basis to: (i) characterize early visual capacities and consequently to enable early interventions; (ii) compare risk groups and follow visual development over time; and (iii), construct an individual visual profile for each child.

A method is described to quantify the quality of visual information processing based on reflexive eye movements in response to specific visual modalities. Reaction times and fixation output parameters are used to characterize visual performance in children with and without visual impairments from 6 months of age.

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational ...

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.

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. ...

Central and Divided Visual Field Presentation of Emotional Images to Measure Hemispheric Differences in Motivated Attention

Two dominant theories on lateralized processing of emotional information exist in the literature. One theory posits that unpleasant emotions are processed by right frontal regions, while pleasant emotions are processed by left frontal regions. The other theory posits that the right hemisphere is more specialized for the processing of emotional information overall, particularly in posterior regions.
Assessing the different roles of the cerebral hemispheres in processing emotional information can be difficult without the use of neuroimaging methodologies, which are not accessible or affordable to all scientists. Divided visual field presentation of stimuli can allow for the investigation of lateralized processing of information without the use of neuroimaging technology. 
This study compared central versus divided visual field presentations of emotional images to assess differences in motivated attention between the two hemispheres. The late positive potential (LPP) was recorded using electroencephalography (EEG) and event-related potentials (ERPs) methodologies to assess motivated attention. Future work will pair this paradigm with a more active behavioral task to explore the behavioral impacts on the attentional differences found.

This study compared central versus divided visual field presentations of emotional images to assess differences in motivated attention between the two hemispheres. The late positive potential (LPP) was recorded using electroencephalography (EEG) and event-related potentials (ERPs) methodologies to assess motivated attention.

Two dominant theories on lateralized processing of emotional information exist in the literature. One theory posits that unpleasant emotions are processed ...

Eye Tracking During Visually Situated Language Comprehension: Flexibility and Limitations in Uncovering Visual Context Effects

The present work is a description and an assessment of a methodology designed to quantify different aspects of the interaction between language processing and the perception of the visual world. The recording of eye-gaze patterns has provided good evidence for the contribution of both the visual context and linguistic/world knowledge to language comprehension. Initial research assessed object-context effects to test&#160;theories of modularity in language processing. In the introduction, we describe how subsequent investigations have taken the role of the wider visual context in language processing as a research topic in its own right, asking questions such as how our visual perception of events and of speakers contributes to&#160;comprehension informed by&#160;comprehenders&#39; experience. Among the examined aspects of the visual context are actions, events, a speaker&#39;s gaze, and emotional facial expressions, as well as spatial object configurations. Following an overview of the eye-tracking method and its different applications, we list the key steps of the methodology in the protocol, illustrating how to successfully use it to study visually-situated language comprehension. A final section presents three sets of representative results and illustrates the benefits and limitations of eye tracking for investigating the interplay between the perception of the visual world and language comprehension.

The present article reviews an eye-tracking methodology for studies on language comprehension. To obtain reliable data, key steps of the protocol must be followed. Among these are the correct set-up of the eye tracker (e.g., ensuring good quality of the eye and head images) and accurate calibration.

The present work is a description and an assessment of a methodology designed to quantify different aspects of the interaction between language processing ...

Using Eye Movements Recorded in the Visual World Paradigm to Explore the Online Processing of Spoken Language

In a typical eye tracking study using the visual world paradigm, participants' eye movements to objects or pictures in the visual workspace are recorded via an eye tracker as the participant produces or comprehends a spoken language describing the concurrent visual world. This paradigm has high versatility, as it can be used in a wide range of populations, including those who cannot read and/or who cannot overtly give their behavioral responses, such as preliterate children, elderly adults, and patients. More importantly, the paradigm is extremely sensitive to fine grained manipulations of the speech signal, and it can be used to study the online processing of most topics in language comprehension at multiple levels, such as the fine grained acoustic phonetic features, the properties of words, and the linguistic structures. The protocol described in this article illustrates how a typical visual world eye tracking study is conducted, with an example showing how the online processing of some semantically complex statements can be explored with the visual world paradigm.

The visual world paradigm monitors participants' eye movements in the visual workspace as they are listening to or speaking a spoken language. This paradigm can be used to investigate the online processing of a wide range of psycholinguistic questions, including semantically complex statements, such as disjunctive statements.

In a typical eye tracking study using the visual world paradigm, participants' eye movements to objects or pictures in the visual workspace are recorded ...

Visual Classical Conditioning in Wood Ants

Several species of insects have become model systems for studying learning and memory formation. Although many studies focus on freely moving animals, studies implementing classical conditioning paradigms with harnessed insects have been important for investigating the exact cues that individuals learn and the neural mechanisms underlying learning and memory formation. Here we present a protocol for evoking visual associative learning in wood ants through classical conditioning. In this paradigm, ants are harnessed and presented with a visual cue (a blue cardboard), the conditional stimulus (CS), paired with an appetitive sugar reward, the unconditional stimulus (US). Ants perform a Maxilla-Labium Extension Reflex (MaLER), the unconditional response (UR), which can be used as a readout for learning. Training consists of 10 trials, separated by a 5-minute intertrial interval (ITI). Ants are also tested for memory retention 10 minutes or 1 hour after training. This protocol has the potential to allow researchers to analyze, in a precise and controlled manner, the details of visual memory formation and the neural basis of learning and memory formation in wood ants.

We present a protocol for the classical conditioning of harnessed ants that permits researchers to study visual learning and memory formation at a level of analysis not possible with freely moving individuals.

Several species of insects have become model systems for studying learning and memory formation. Although many studies focus on freely moving animals, ...

Eye-tracking to Distinguish Comprehension-based and Oculomotor-based Regressive Eye Movements During Reading

Regressive eye movements are eye movements that move backwards through the text and comprise approximately 10-25% of eye movements during reading. As such, understanding the causes and mechanisms of regressions plays an important role in understanding eye movement behavior. Inhibition of return (IOR) is an oculomotor effect that results in increased latency to return attention to a previously attended target versus a target that was not previously attended. Thus, IOR may affect regressions. This paper describes how to design materials to distinguish between regressions caused by comprehension-related and oculomotor processes; the latter is subject to IOR. The method allows researchers to identify IOR and control the causes of regressions. While the method requires tightly controlled materials and large numbers of participants and materials, it allows researchers to distinguish and control the types of regressions that occur in their reading studies.

The method was designed to investigate the role of inhibition of return (IOR) in regressive eye movements during reading. The focus is on differentiating between regressions triggered as a result of comprehension difficulty versus those triggered from oculomotor error, including the role of IOR in the two types of regressions.

Regressive eye movements are eye movements that move backwards through the text and comprise approximately 10-25% of eye movements during reading. As ...

Gaze in Action: Head-mounted Eye Tracking of Children's Dynamic Visual Attention During Naturalistic Behavior

Young children's visual environments are dynamic, changing moment-by-moment as children physically and visually explore spaces and objects and interact with people around them. Head-mounted eye tracking offers a unique opportunity to capture children's dynamic egocentric views and how they allocate visual attention within those views. This protocol provides guiding principles and practical recommendations for researchers using head-mounted eye trackers in both laboratory and more naturalistic settings. Head-mounted eye tracking complements other experimental methods by enhancing opportunities for data collection in more ecologically valid contexts through increased portability and freedom of head and body movements compared to screen-based eye tracking. This protocol can also be integrated with other technologies, such as motion tracking and heart-rate monitoring, to provide a high-density multimodal dataset for examining natural behavior, learning, and development than previously possible. This paper illustrates the types of data generated from head-mounted eye tracking in a study designed to investigate visual attention in one natural context for toddlers: free-flowing toy play with a parent. Successful use of this protocol will allow researchers to collect data that can be used to answer questions not only about visual attention, but also about a broad range of other perceptual, cognitive, and social skills and their development.

Young children do not passively observe the world, but rather actively explore and engage with their environment. This protocol provides guiding principles and practical recommendations for using head-mounted eye trackers to record infants' and toddlers' dynamic visual environments and visual attention in the context of natural behavior.

Young children's visual environments are dynamic, changing moment-by-moment as children physically and visually explore spaces and objects and interact ...

Investigating the Deployment of Visual Attention Before Accurate and Averaging Saccades via Eye Tracking and Assessment of Visual Sensitivity

This experimental protocol was designed to investigate whether visual attention is obligatorily deployed at the endpoint of saccades. To this end, we recorded the eye position of human participants engaged in a saccade task via eye tracking and assessed visual orientation discrimination performance at various locations during saccade preparation. Importantly, instead of using a single saccade target paradigm for which the saccade endpoint typically coincides roughly with the target, this protocol comprised the presentation of two nearby saccade targets, leading to a distinct spatial dissociation between target locations and saccade endpoint on a substantial number of trials. The paradigm allowed us to compare presaccadic visual discrimination performance at the endpoint of accurate saccades (landing at one of the saccade targets) and of averaging saccades (landing at an intermediate location in between the two targets). We observed a selective enhancement of visual sensitivity at the endpoint of accurate saccades but not at the endpoint of averaging saccades. Rather, before the execution of averaging saccades, visual sensitivity was equally enhanced at both targets, suggesting that saccade averaging follows from unresolved attentional selection among the saccade targets. These results argue against a mandatory coupling between visual attention and saccade programming based on a direct measure of presaccadic visual sensitivity rather than saccadic reaction times, which have been used in other protocols to draw similar conclusions. While our protocol provides a useful framework to investigate the relationship between visual attention and saccadic eye movements at the behavioral level, it can also be combined with electrophysiological measures to extend insights at the neuronal level.

This experimental protocol combined eye tracking and the assessment of presaccadic visual sensitivity in a dual task paradigm, consisting of a free choice saccade task and a visual discrimination task, to investigate the deployment of visual spatial attention before both, accurate and averaging saccades.

This experimental protocol was designed to investigate whether visual attention is obligatorily deployed at the endpoint of saccades. To this end, we ...