Name: how to build a dichoptic presentation system that includes an eye tracker
Uploaded: 2017-09-06T14:00:00
Description: Watch this Scientific Journal Video about How to Build a Dichoptic Presentation System That Includes an Eye Tracker at JoVE.com

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.

how-to-build-dichoptic-presentation-system-that-includes-an-eye

Research

JoVE Journal

Behavior

Eye Tracking, Cortisol, and a Sleep vs. Wake Consolidation Delay: Combining Methods to Uncover an Interactive Effect of Sleep and Cortisol on Memory

Although rises in cortisol can benefit memory consolidation, as can sleep soon after encoding, there is currently a paucity of literature as to how these two factors may interact to influence consolidation. Here we present a protocol to examine the interactive influence of cortisol and sleep on memory consolidation, by combining three methods: eye tracking, salivary cortisol analysis, and behavioral memory testing across sleep and wake delays. To assess resting cortisol levels, participants gave a saliva sample before viewing negative and neutral objects within scenes. To measure overt attention, participants&#8217; eye gaze was tracked during encoding. To manipulate whether sleep occurred during the consolidation window, participants either encoded scenes in the evening, slept overnight, and took a recognition test the next morning, or encoded scenes in the morning and remained awake during a comparably long retention interval. Additional control groups were tested after a 20&#160;min&#160;delay in the morning or evening, to control for time-of-day effects. Together, results showed that there is a direct relation between resting cortisol at encoding and subsequent memory, only following a period of sleep. Through eye tracking, it was further determined that for negative stimuli, this beneficial effect of cortisol on subsequent memory may be due to cortisol strengthening the relation between where participants look during encoding and what they are later able to remember. Overall, results obtained by a combination of these methods uncovered an interactive effect of sleep and cortisol on memory consolidation.

We present a protocol used to discover an interactive effect between sleep and cortisol on memory consolidation, particularly for negative arousing images. Specifically, the experimental design utilizes eye tracking, salivary cortisol analysis, and behavioral memory testing &#8211; methods that can be used with both healthy and clinical participants.

Although rises in cortisol can benefit memory consolidation, as can sleep soon after encoding, there is currently a paucity of literature as to how these ...

Assessment of Murine Exercise Endurance Without the Use of a Shock Grid: An Alternative to Forced Exercise

Using laboratory mouse models, the molecular pathways responsible for the metabolic benefits of endurance exercise are beginning to be defined. The most common method for assessing exercise endurance in mice utilizes forced running on a motorized treadmill equipped with a shock grid. Animals who quit running are pushed by the moving treadmill belt onto a grid that delivers an electric foot shock; to escape the negative stimulus, the mice return to running on the belt. However, avoidance behavior and psychological stress due to use of a shock apparatus can interfere with quantitation of running endurance, as well as confound measurements of postexercise serum hormone and cytokine levels. Here, we demonstrate and validate a refined method to measure running endurance in na&#239;ve C57BL/6 laboratory mice on a motorized treadmill without utilizing a shock grid. When mice are preacclimated to the treadmill, they run voluntarily with gait speeds specific to each mouse. Use of the shock grid is replaced by gentle encouragement by a human operator using a tongue depressor, coupled with sensitivity to the voluntary willingness to run on the part of the mouse. Clear endpoints for quantifying running time-to-exhaustion for each mouse are defined and reflected in behavioral signs of exhaustion such as splayed posture and labored breathing. This method is a humane refinement which also decreases the confounding effects of stress on experimental parameters.

A method to assess exercise endurance in laboratory mice without the use of a shock grid is demonstrated. This method is a humane refinement that can decrease the confounding effects of stress on experimental parameters.

Using laboratory mouse models, the molecular pathways responsible for the metabolic benefits of endurance exercise are beginning to be defined. The most ...

A Dual Task Procedure Combined with Rapid Serial Visual Presentation to Test Attentional Blink for Nontargets

When viewers search for targets in a rapid serial visual presentation (RSVP) stream, if two targets are presented within about 500 msec of each other, the first target may be easy to spot but the second is likely to be missed. This phenomenon of attentional blink (AB) has been widely studied to probe the temporal capacity of attention for detecting visual targets. However, with the typical procedure of AB experiments, it is not possible to examine how the processing of non-target items in RSVP may be affected by attention. This paper describes a novel dual task procedure combined with RSVP to test effects of AB for nontargets at varied stimulus onset asynchronies (SOAs). In an exemplar experiment, a target category was first displayed, followed by a sequence of 8 nouns. If one of the nouns belonged to the target category, participants would respond &#8216;yes&#8217; at the end of the sequence, otherwise participants would respond &#8216;no&#8217;. Two 2-alternative forced choice memory tasks followed the response to determine if participants remembered the words immediately before or after the target, as well as a random word from another part of the sequence. In a second exemplar experiment, the same design was used, except that 1) the memory task was counterbalanced into two groups with SOAs of either 120 or 240 msec and 2) three memory tasks followed the sequence and tested remembrance for nontarget nouns in the sequence that could be anywhere from 3 items prior the target noun position to 3 items following the target noun position. Representative results from a previously published study demonstrate that our procedure can be used to examine divergent effects of attention that not only enhance targets but also suppress nontargets. Here we show results from a representative participant that replicated the previous finding.&#160;

This paper describes a novel dual task procedure combined with Rapid Serial Visual Presentation to look at attentional blink at varied stimulus onset asynchronies. This experimental procedure differed from others in that it tested attentional blink for nontargets.

When viewers search for targets in a rapid serial visual presentation (RSVP) stream, if two targets are presented within about 500 msec of each other, the ...

How to Study Placebo Responses in Motion Sickness with a Rotation Chair Paradigm in Healthy Participants

Placebo responses occur in every medical intervention when patients or participants expect to receive an effective treatment to relieve symptoms. However, underlying mechanisms of placebo responses are not fully understood. It has repeatedly been shown that placebo responses are associated with changes in neural activity but for many conditions it is unclear whether they also affect the target organ, such as the stomach in motion sickness. Therefore, we present a methodology for the multivariate assessment of placebo responses by subjective, behavioral and objective measures in motion sickness with a rotation chair paradigm. The physiological correlate of motion sickness is a shift in gastric myoelectrical activity towards tachygastria that can be recorded with electrogastrography. The presented study applied the so-called balanced placebo design (BPD) to investigate the effects of ginger compared to placebo and the effects of expectations by verbal information. However, the study revealed no significant main or interactional effects of ginger (as a drug) or information on outcome measures but showed interactions when sex of participants and experimenters are taken into considerations. We discuss limitations of the presented study and report modifications that were used in subsequent studies demonstrating placebo responses when rotation speed was lowered. In general, future placebo studies have to identify the appropriate target organ for the studied placebo responses and to apply the specific methods to assess the physiological correlates.

An experimental rotation chair paradigm is used to investigate whether a placebo intervention on motion sickness affects subjective outcome measures only or also affects behavioral and objective measures in a balanced placebo design.

Placebo responses occur in every medical intervention when patients or participants expect to receive an effective treatment to relieve symptoms. However, ...

Eye-Tracking Control to Assess Cognitive Functions in Patients with Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with pathological involvement of upper and lower motoneurons, subsequently leading to progressive loss of motor and speech abilities. In addition, cognitive functions are impaired in a subset of patients. To evaluate these potential deficits in severely physically impaired ALS patients, eye-tracking is a promising means to conduct cognitive tests. The present article focuses on how eye movements, an indirect means of communication for physically disabled patients, can be utilized to allow for detailed neuropsychological assessment. The requirements, in terms of oculomotor parameters that have to be met for sufficient eye-tracking in ALS patients are presented. The properties of stimuli, including type of neuropsychological tests and style of presentation, best suited to successfully assess cognitive functioning, are also described. Furthermore, recommendations regarding procedural requirements are provided. Overall, this methodology provides a reliable, easy to administer and fast approach for assessing cognitive deficits in patients who are unable to speak or write such as patients with severe ALS. The only confounding factor might be deficits in voluntary eye movement control in a subset of ALS patients.

Cognitive deficits are common in about one third of patients with amyotrophic lateral sclerosis, a neurological condition leading to progressive impairments in speech and movement abilities. To conduct cognitive tests in patients unable to speak or write a reliable and easy to administer eye-tracking paradigm was developed.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with pathological involvement of upper and lower motoneurons, subsequently leading to ...

The Other End of the Leash: An Experimental Test to Analyze How Owners Interact with Their Pet Dogs

It has been suggested that the way in which owners interact with their dogs can largely vary and influence the dog-owner bond, but very few objective studies, so far, have addressed how the owner interacts with the dog. The goal of the present study was to record dog owners&#39; interaction styles by means of objective observation and coding. The experiment included eight standardized situations in which owners of pet dogs were asked to perform specific tasks including both positive (i.e. playing, teaching a new task, showing a preference towards an object in a food searching task, greeting after separation) and potentially distressing tasks (i.e. physical restriction during DNA sampling, putting a T-shirt onto the dog, giving basic obedience commands while the dog was distracted). The video recordings were coded off-line using a specifically designed coding scheme including scores for communication, social support, warmth, enthusiasm, and play style, as well as frequency of behaviors like petting, praising, commands, and attention sounds. Exploratory Factor Analysis of the 20 variables measured revealed 3 factors, labeled as Owner Warmth, Owner Social Support, and Owner Control, which can be viewed as analogues to parenting style dimensions. The experimental procedure introduced here represents the first standardized measure of interaction styles of dog owners. The methodology presented here is a useful tool to investigate individual variation in the interaction style of pet dog owners that can be used to explain differences in the dog-human relationship, dogs&#39; behavioral outcomes, and dogs stress coping strategies, all crucial elements both from a theoretical and applied point of view.

This article presents eight different experimental tasks, mirroring the everyday life of dogs and owners, used to analyze how owners interact with their dogs in a standardized way. The tasks included both positive (e.g. play) and negative (potentially stressful) situations (e.g. physical restriction).

It has been suggested that the way in which owners interact with their dogs can largely vary and influence the dog-owner bond, but very few objective ...

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 ...

Using Rapid Serial Visual Presentation to Measure Set-Specific Capture, a Consequence of Distraction While Multitasking

This method uses a rapid serial visual presentation (RSVP) paradigm to measure the cost of distraction when participants maintain multiple search goals. The protocol identifies two types of distraction within a single task - contingent attentional capture and set-specific capture - that represent different types of limitations of cognitive processing. Participants search for letters in two or more &#34;target&#34; ink colors (e.g., green and orange) within a continuous RSVP stream of heterogeneously colored letters, while ignoring two peripheral RSVPs of letters. Upon detecting a target, participants are to identify the letter. On some trials, target-colored distractors appear in the periphery just prior to the presentation of a target, causing a drop in target identification performance. Contingent attentional capture is observed by examining performance on trials in which the peripheral distractor is the same color as the target on that trial (e.g., both orange). Set-specific capture is represented by performance on trials in which the peripheral distractor is target-colored (e.g., orange), but not the same color as the target on that trial (e.g., green.) By varying the amount of time (i.e., the number of stimuli appearing) between the presentation of the distractor and the target, researchers can observe how participants recover from these distraction costs over time. As compared to static displays that are often used to measure contingent attentional capture, the dynamic display produces much larger effects, allowing the researcher to identify subtle effects of smaller manipulations. An unusual aspect of our design is that it employs a continuous display; &#34;filler&#34; stimuli connect one trial to the next seamlessly, and participants respond during this interval whenever they detect a target. The continuous display reduces chance performance to near-zero levels (rather than 50%) and provides researchers with a more sensitive measure of performance differences across trial types.

This method uses a dynamic visual display to index costs of distraction during visual search, including both &#34;contingent attentional capture&#34; and &#34;set-specific capture,&#34; which is a cost of distraction that occurs when the participants maintain multiple search goals simultaneously. This method has revealed basic mechanisms and limitations of visual attention.

This method uses a rapid serial visual presentation (RSVP) paradigm to measure the cost of distraction when participants maintain multiple search goals. ...

Olfactory Context Dependent Memory: Direct Presentation of Odorants

Information is retrieved more effectively when the retrieval occurs in the same context as that in which the information was first encoded. This is termed context dependent memory (CDM). One category of cues that have been shown to effectively produce CDM effects are odors. However, it is unclear what the boundary conditions of these CDM effects are. In particular, given that olfaction has been called an implicit sense, it is possible that odors are only effective mnemonic cues when they are presented in the background. This assertion seems even more likely given that previous research has shown odors to be poor cues during paired associate memory tests, where odors are in the focus of attention as mnemonic cues for other information. In order to determine whether odors are only effective contextual mnemonic cues when presented outside the central focus of an observer, an olfactory CDM experiment was performed in which odorants were presented directly, rather than ambiently. Direct presentation was accomplished with the aid of an olfactometer. The olfactometer not only allows for direct presentation of odorants, but provides other methodological benefits, including the allowance of trial by trial manipulations of odorant presentations and, relatedly, time-specific releases of odorants. The presence of the same odor during both encoding and retrieval enhanced memory performance, regardless of whether the odor was presented ambiently or directly. This finding can serve as a basis for future olfactory CDM research which can utilize the benefits of direct presentation.

The use of an olfactometer for directly presenting odorants opens exciting opportunities for researchers of olfactory memory. The current paper discusses issues related to this methodology as related to a previously published experiment on olfactory context dependent memory.

Information is retrieved more effectively when the retrieval occurs in the same context as that in which the information was first encoded. This is termed ...

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 ...