Dyslexics’ Fragile Oculomotor Control Is Further Destabilized by Increased Text Difficulty

Abstract

Dyslexic adolescents demonstrate deficits in word decoding, recognition, and oculomotor coordination as compared to healthy controls. Our lab recently showed intrinsic deficits in large saccades and vergence movements with a Remobi device independent from reading. This shed new light on the field of dyslexia, as it has been debated in the literature whether the deficits in eye movements are a cause or consequence of reading difficulty. The present study investigates how these oculomotor problems are compensated for or aggravated by text difficulty. A total of 46 dyslexic and 41 non-dyslexic adolescents’ eye movements were analyzed while reading L’Alouette, a dyslexia screening test, and 35 Kilos D’Espoir, a children’s book with a reading age of 10 years. While reading the more difficult text, dyslexics made more mistakes, read slower, and made more regressive saccades; moreover, they made smaller amplitude saccades with abnormal velocity profiles (e.g., higher peak velocity but lower average velocity) and significantly higher saccade disconjugacy. While reading the simpler text, these differences persisted; however, the difference in saccade disconjugacy, although present, was no longer significant, nor was there a significant difference in the percentage of regressive saccades. We propose that intrinsic eye movement abnormalities in dyslexics such as saccade disconjugacy, abnormal velocity profiles, and cognitively associated regressive saccades can be particularly exacerbated if the reading text relies heavily on word decoding to extract meaning; increased number of regressive saccades are a manifestation of reading difficulty and not a problem of eye movement per se. These interpretations are in line with the motor theory of visual attention and our previous research describing the relationship between binocular motor control, attention, and cognition that exists outside of the field of dyslexia.

Disconjugate Eye Movements in Dyslexic Adolescents While Viewing Op Art: A Creative Handicap?

“…While viewing all three paintings, dyslexics demonstrated uncoordinated eye movements that were similar to those that they made while reading, or while making saccades or vergence movements to audiovisual targets, indicating that their eye movement deficits persist while viewing artwork. Specifically, they demonstrated similar abnormal velocity profiles to those seen while making vergence and saccades to audiovisual targets and while reading, i.e., a faster peak velocity, yet a slower average velocity with a significantly longer duration and a slightly smaller amplitude, suggesting a long deceleration tail that has been discussed in previous studies [12,21]. This observation suggests that abnormalities in the velocity profile of eye movements persist while viewing paintings.…”

“…For all three paintings, dyslexics demonstrated a higher duration, a faster peak velocity, and a higher average velocity in saccades made to the left and right while viewing (see Tables 1-3). This oculomotor profile is similar to that found in dyslexics while reading and while making saccades to audiovisual targets [12,21]. For all three paintings, dyslexics demonstrated a lower amplitude while making saccades to the left.…”

“…Interestingly, the eye movement abnormalities that were present while viewing paintings were similar to those present during reading. In comparing these findings with our previous findings in dyslexics while reading, it is important to note that, similarly, dyslexics demonstrate a smaller amplitude, a longer duration, a faster peak velocity, and a slower average velocity while reading and while viewing all three paintings [12,21]. Similarly to reading a difficult text, dyslexics demonstrated a greater disconjugacy while looking at Painting 1, which provokes an illusion of depth.…”

“…The finding that dyslexics may have decreased motion perception would argue that they may be less sensitive to the motion induced by Op art compared with non-dyslexics. However, given that dyslexics have been shown to have a greater instability of their eye movements, would this instability create an increase in their micro-movements so that they actually see a greater “flicker” effect that would generate a greater contrast and a more sensitive reaction as they survey the painting [ 12 , 13 , 21 ]?…”

Predicting Dyslexia and Reading Speed in Adolescents from Eye Movements in Reading and Non-Reading Tasks: A Machine Learning Approach

“…Though there have only been a few studies in the dyslexic population that have demonstrated deficits in eye movements to random targets that stimulate vergence or saccades independent from reading, such studies are essential to assess the existence of eye movement problems per se. For instance, in the dyslexic population, eye movement abnormalities in vergence have been reported using clinical subjective tests since 1988 and in binocular coordination of saccades to LED targets [1][2][3][4][5]. Most recently, Ward and Kapoula conducted a complete study of large saccades and vergence eye movements in depth using LED targets [6].…”