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

The overall goal of this Eye-Tracking-Based Preferential Looking Method, is to quantify the quality of Visual Information Processing in Children, based on Reflexive Visually-guided Orienting Responses. This method's gonna have significant value in the field of Clinical Visual Assessments and Rehabilitation in Children from six months of age. Also, the methods is based on objective measurements, and analysis of eye movement responses.

These responses provide quantitative information about visual performance, and can be obtained without verbal communication. The quantitative visual processing parameters, such as reaction times, and fixation quality, have additional value for characterizing visual performance, especially in young children, and children with intellectual disabilities. The implications of this matter, extend from characterizing visual processing, and ocular motor functions in healthy children, to identification of abnormal visual performance in children with visual impairments.

Begin by selecting a set of visual stimuli, such as images or movies, to target the processing of basic ocular motor functions, and visual processing functions. Use visual stimuli, to evaluate basic ocular motor functions, such as Fixations and Saccades, Smooth Pursuit, and Optokinetic Nystagmus. Next, use a set of visual stimuli, that are based on a Four Alternative-forced Choice Preferential-looking Paradigm, such that four different stimulus corners, each represent an alternative choice, or a target area.

Use these visual stimuli, to evaluate visual processing functions, such as simultaneous processing, form, contrast, color, or motion. Next, design a test sequence in the Eye-tracker software, by selecting the type of stimulus to be added, either an image or movie. To do this, select the desired stimulus from the folder in which it is located, and click Add.

Repeat these steps until all stimuli have been added to the timeline. Finally, place the different types of visual stimuli, in random order, in the test sequence. Ensure that the position of the target area, alternates from trial to trial, in order to engage reflexive eye movements, toward the target, from the participant.

Begin by choosing an eye-tracking system that is suitable for pediatric populations, for example, with remote infrared light, and attach the eye-tracker monitor with a flexible LCD arm, to a solid table. Choose an arm that can move in three dimensions. Escort the child into the testing room, and position them at about 60 centimeters from the monitor, to ensure efficient pupil-tracking of both eyes.

Then, adjust the monitor position, to be perpendicular to the child's eyes. Next, confirm the quality of pupil reception, by the presence of two clearly visible white dots, that represent the child's eyes on the screen. Start the Eye-tracker Software Calibration Procedure, that presents moving dots in predefined areas of the monitor, to align the gaze positions.

Check the quality of this preset calibration, to ensure recordings can be made. Next, activate a separate window called viewer, that chose the child's eye movement responses, to the test stimuli, by superimposing the gaze signal, on the video recording. Activate a web camera that is directed at the child, to observe and record the child's general behavior, during the test.

Tell the child that they will be watching television. Then, execute the test, and observe the child's physical behavior, and eye movement responses. After test execution, replay the gaze recording offline, and observe the gaze responses to the presented stimuli, in order to obtain a qualitative characterization of the child's visual orienting behavior.

Finally, export and store each subject's recorded, time-based data on eye movement characteristics, such as viewing distance and gaze positions, and separately the time-based list of presented visual stimuli, such as stimulus positions. Apply a post-calibration procedure after the recording is complete, to circumvent poor pre-test calibration, due to excessive head movements, lack of proper fixations, and abnormal gaze or head position. To do this, open the Analysis software, and select the stimulus to analyze the gaze data, by typing in one next to the stimulus of choice.

Press Run. In the Pop-up Menu, select the option Post-calibrate the Data. Then, select Gaze Data for one subject, from the list of files and press Open.

From the next Pop-up Menu, select which eyes to analyze. Either Left, Right, or Both, in order to generate a scatter plot, of all recorded gaze and target positions, over the total stimulus presentation time. Next, select Yes or No, depending on whether gaze positions, correctly overlap with the corresponding target positions.

If the calibration is not correct, choose No to perform a post-calibration. Translate the center of gaze points, to the center of the monitor, by clicking once, on the Center of Gaze Points, or the Center Point located exactly in the middle of the vertical and horizontal axis. Scale the gaze positions to the corresponding target positions, by clicking the Center of Gaze Points, in each of the four target quadrants once.

Check again, whether the gaze positions correctly overlap, with the corresponding target positions. If the calibration is correct, choose Yes, to Save the calibrated gaze data. Otherwise, choose No, and repeat the post-calibration procedure.

Furthermore, verify that the subject has seen the stimulus presentation, by checking that the gaze data, aligns with the following criteria, as well as the visualization graph. If the stimulus can be classified as seen, click Yes in the Pop-up Menu. Otherwise, click No.Simultaneously, plot all fixation points, belonging to the presented stimulus, in the corresponding target quadrant.

Visually inspect whether the fixation points, are located in the correct quadrant. Finally, after manually checking the eye movement responses, use the software to calculate three parameters. Reaction Time to Fixation, or RTF, Fixation Duration, or FD, and Gaze Fixation Area, or GFA.

RTF, is a measure for the time that is needed, to process visual information, and execute an eye movement. Here, the average RTF values during the dynamic cartoon stimulus, are significantly higher, in children with visual impairments, compared to children without visual impairments. In addition, RTF values are significantly higher, in children with cerebral visual impairments, compared to children with ocular visual impairments.

Fixation Duration, is the total amount of time, that gaze was fixation within the target area. FD is significantly shorter, in children with visual impairments, compared to children without visual impairments. In addition, FD is significantly shorter, in children with cerebral visual impairments, compared to children with ocular visual impairments.

Furthermore, Gaze Fixation Area, is a measure for fixation accuracy, in which a small area of fixation, indicates high fixation accuracy. Here, GFA values are significantly larger, in children with visual impairments, then in children without visual impairments. In addition, GFA is significantly larger, in children with visual impairments and nystagmus, compared to children with visual impairments, but without nystagmus.

After watching this video, you should have a good understanding how to use Eye-tracking-based Methods, in clinical and practice. These methods can be used to quantify, the quality of visual information processing, in children from the age of six months. Essential steps within the protocol, include the stimuli that are based on preferential looking, the ability to post-calibrate the eye-tracking data, and the availability of quantitative outcome issues.

The official processing parameters obtained with these methods, can be advantageous for following visual developments over time, and for monitoring effects of Visual Intervention Programs. These methods can provide individual profiles of visual performance. Such profiles may be used for functional support in daily life, tailored to the child's needs.