Trenton Jackman and Dr. Steven Luke, Psychology Department

Introduction

Reading is a part of everyday life. Humans read street signs, textbooks, emails, manuals, novels, and many other things. While reading we move our eyes 2-4 times per second. Each movement is called a saccade, and each pause between movements is called a fixation. These eye-movements allow us to move our fovea (area on the retina that is responsible for sharp central vision) to attend to pertinent information in the world. While reading, or just looking around, we don’t think about moving our eyes; our brain does this instantly and innately.

Previous research has looked at the neural networks that control eye-movements during voluntary conscious eye-movements. For example, previous studies had participants look at a stimulus when it appeared, and then they mapped the networks using neuro-imaging techniques. This has been the common theme in the area of eye-movement research; however, it does not apply to real unconscious eye-movements. An advantage to tracking eye-movement while reading is that reading is so practiced that it has become reflexive. Little has been done looking at the neural networks of involuntary reflexive eye-movements, such as those made during a reading task.

By pairing fMRI technology with eye-tracking technology, we can take advantage of the strength of each data method. MRI has good spatial resolution, however lacks in temporal resolution– it’s hard to know exactly what the participant was doing when activation is seen in brain. The eye-tracking however, gives us a time stamped data point that tells us exactly at which word they were looking, or if they were performing a saccade. Combining these two technologies is novel and exciting, and BYU is one of the only places in the world that has the expertise to perform this experiment (Henderson, Choi, Luke & Desai, 2015). This research project aims to look at the areas of the brain involved in deciding how far to move our eyes (saccade amplitude) and how long it takes to start moving our eyes (saccadic latency).

Methods

After removal of a few participants because of bad data, forty-three participants remained. All participants were from Brigham Young University, and gave informed consent to participate in this study. All participants received 6 SONA credits (BYU Psychology Research Participation Credit) for one hour of participation in the study.

An eye-tracking program was created using the simple text passages from popular online news sources. While in an MRI scanner, participants used a mirror to read the passages from a computer screen while their eye-movements were tracked using aResearch Eyelink 1000 eye-tracker. The MRI scans and the eye-tracking program were synced to the same clock allowing for a precise integration of MRI and eye tracking data. MRI data was analyzed using AFNI software (Analysis of Functional NeuroImages).

Results

Amplitude: Saccade amplitude is how far we move our eyes. The areas of the brain that seemed to correlate with decisions of how far to move our eyes were the temporal gyrus, frontal eye fields, and the cerebellum. Latency: Saccade latency is the decision of when to move our eyes. The areas of the brain that were correlated with decisions of when to move were the lingual gyrus, frontal eye fields, and the supplementary eye fields.

Figure 1 to the left is a conglomerate of all participants scans fit into a standard model brain and areas of activation circled and labeled. The temporal lobe deals with language processing. The frontal eye fields are involved in controlling where we look. The lingual gyrus is known to be involved in visual language processing.

Discussion

The results confirm our expectations that the superior colliculus and frontal eye field regions of the brain would be involved in the planning of saccades during reading, while the areas of the brain involved in visual and language processing (specifically the lingual gyrus and temporal lobe), as well as regions involved in self-control will be involved in latency.

Establishing a basal level of what is normal for neural control of eye-movements during a reading task will allow for better diagnostic tools for many brain health issues (traumatic brain injury, stroke, dyslexia, etc.). This will open the door to targeted therapies to help these individuals improve their day to day functioning. It could also give more of an understanding as to why certain people suffer from dyslexia.

Conclusion

The current study is the first step of many in understanding the neural networks of the brain during a reading task. Further research should continue to explore the neural networks of eye-movement control in other reflexive tasks like scene search, online browsing or shopping. Researchers should also study the change exhibited by the brain in these reflexive eye control networks (like reading) after someone suffers a stroke or traumatic brain injuries. Understanding these differences from a normal level established by the current study would be the best way to further research and make the work applicable to helping a human population.