Press release

 

Dyslexia and oculomotricity

Paris, November 12, 2002
 

The Cognitive Oculomotricity Club organized a two-day open seminar on the theme "Dyslexia, oculomotor problems and attention and learning difficulties". The seminar was organized by Zoï KAPOULA, CNRS research director, Maria-Pia BUCCI, CNRS researcher (Laboratoire de physiologie de la perception et de l’action, LPPA, CNRS - Collège de France) and Françoise VITU, CNRS researcher (Laboratoire de psychologie expérimentale, LPE, CNRS – University of Grenoble 2 – University of Savoie). This operation was sponsored by the Ile-de-France Network of Cognitive Sciences and the French government’s Research Ministry and received support from ATOL Les Opticiens. The campaign was conducted in Paris on the 27th and 28th of September, 2002. The following is a summary of the main scientific themes that were presented and discussed.

The seminar, initially organized to encourage professional exchanges between a small number of dyslexia researchers and oculomotricity researchers, eventually attracted the interest of a much larger public from a wide range of disciplinary backgrounds. More than 150 people took part in the two-day seminar, including a number of speech-language pathologists and orthopticians, doctors (pediatricians, ophthalmologists, school doctors, etc.), psychologists, secondary teachers, researchers, research teaching directors, professors from various European universities, and opticians.
In her introduction, Zoï Kapoula underscored the remarkable incidence of reading difficulties and dyslexia when learning to read, especially among boys. She also said that the complexity and controversial etiology of dyslexia heightened the urgent need for an interdisciplinary approach, both in terms of fundamental research and patient care and assistance.

Liliane Sprenger Charolles, director of research at the CNRS (Child Speech Pathology and Language Acquisition Laboratory, CNRS – University of Paris 5), stressed the prevalence of a phonological deficit in dyslexic patients, while acknowledging the importance of a thorough examination of potential visual and oculomotor problems.

Carine Royer, of the Experimental Psychology Laboratory (LPE, CNRS – University of Grenoble 2 – University of Savoie), revealed the existence of compensatory strategies among dyslexic patients, primarily based on word morphology.

Severine Casalis (URECA, UFR, University of Lille 3), introduced studies unequivocally showing that there is no link between dyslexia and intellectual quotient.

Sylviane Valdois, researcher at the CNRS (LPE), presented the findings of an in-depth study on phonological and visual processing deficits in dyslexia. The frequency of the latter has been shown to be very high. Furthermore, visual attentional performance tests developed by the researcher and her co-workers were shown to be the best predictive indicator of reading performance.

Isabelle Eyom and Cécile Malecot, speech-language pathologists, reviewed the clinical case of a dyspraxic and dyslexic child, whose performance was improved by visual attentional reeducation.

In the afternoon, Françoise Vitu, presented a comparative study of the oculomotor behavior of 10- to 12-year-old school children when reading and compared their results to adults. The considerable strategic regularity of eye tracking in reading words identified by adults (the eye’s landing position is directed preferably towards the center of a word) is acquired by children; but fixation time is longer and more variable, regressive saccades (verification saccades) are more frequent – and more time consuming. Françoise Vitu said this difference in oculomotor behavior calls for cognitive interpretation and added that oculomotor studies would be useful in better understanding the deficits of dyslexic subjects.

Laurent Sparrow, professor-researcher at the University of Lille 3, presented a pilot study in which the oculomotor behavior of five dyslexic subjects was observed as they read several lines of text. Though no anomalies were detected at the beginning of the session, abnormally long pauses appeared later, particularly when unusual French words were encountered.

The meeting then took a more didactic turn with a review of the fundamental aspects of oculomotor physiology involved in the reading process. Zoï Kapoula stressed that if there was a visual component to reading, there was also an entirely distinct motor component. While reading, the central nervous system exercises simultaneous, three-dimensional control over the movements of both eyes (horizontal, vertical, and depth of field). In reading, if the eye moves in a linear direction from left to right with horizontal saccades each followed by a fixation, the jump from one line of text to the next involves an oblique motion (downward and to the left), which requires the deployment of six extra-ocular muscles. As reading is a particularly near vision activity, the brain must adjust the visual angle axes to the right distance and maintain this throughout the text-scanning process. Without good vergance control, words may be fuzzy or wobble, impeding the reading process. Many readers (adults and children) have a limited capacity to control vergence, which is by far the most fragile of all eye movements.

On the same subject, doctor Qing Yang and his co-workers (LPPA, CNRS-Collège-de-France) introduced recent studies in children 4 to 13 years of age showing that eye movement latency (the preparation time) is very long and varies widely in young children (400 ms). Adult latency levels aren’t reached until between 10 and 12 years of age, particularly near vision convergence, which has the longest latency. The latency period in young children is attributed to the gradual maturation of the cortical circuit that is activated during the preparation of movements, notably in the frontal cortex. The study’s authors stressed this must be taken into account in the performance of young children, particularly those who have difficulty learning to read.

Maria Pia Bucci and co-workers (LPPA) introduced an oculomotor study of children suffering from cephalalgia and balance disorders without associated vestibular dysfunction. The oculomotor study did reveal an abnormal reaction time in the children’s eye movements compared to unaffected children of the same age. A considerable discrepancy in near vision convergence was observed. Most notably, the study demonstrated that orthoptic vergence reeducation was instrumental in reducing eye movement initiation times to normal levels. Also noteworthy were the results of a questionnaire sent to the parents of these children, which revealed that 28% suffered from reading disorders.

The session ended with the video presentation of recorded sequences of eye movements using a video system (Chronos, SKALAR Medical, Holland). The sequences were recorded by Zoï Kapoula’s team at the Collège de France laboratory.


Zoï Kapoula opened the September 28 session in the Auditorium of the Georges Pompidou European Hospital with a speech underscoring the need to constantly monitor eye convergence by the central nervous system during reading, a near visual activity. She continued with a presentation of EEG studies, which identified significant posterior cortical activation during eye movement latency in humans for the first time.
First observation: Vergence, and particularly convergence, provokes the highest cortical activation, activation that is symmetrically distributed over both hemispheres, while in the case of a saccade, the activation is lateralized on the contralateral hemisphere with respect to the direction of the saccade.
Second observation: In near vision, in the peripersonal space implicated in reading, the parietal region is more active, which shows a cortical representation of space that differs depending on the distance, whether near or far. The parietal cortex plays a major role in controlling attention, eye movements, and spatial orientation; furthermore, lesions of the parietal cortex provoke deficiencies that have also been observed in dyslexic patients.

Doctor Monica Biscaldi, of the University of Freiburg, further elaborated the issue of cortical control of eye movements while reading with a study on the inhibition of reflex movements by voluntarily controlling the redirection of eye fixation. Her team, using a battery of neurological oculomotor tests, revealed a greater number of reflexive saccades as well as inappropriate movements in reflex movement inhibition tasks among dyslexic subjects. A daily oculomotor reeducation program, of the “game boy” type, was shown to enhance oculomotor performance. Indirectly, reading performance also improved. In conclusion, the improvement mechanism may be perceptive, attentional, oculomotor, or even multifactorial.

Professor Yan Ygge of the Karolinska Institute, Stockholm, introduced studies showing a sensitivity variance in the perception of movement between dyslexic and normal readers, these observations are compatible with a theory suggesting a magnocellular defect in developmental dyslexia.

Finally, professor John Stein, of the University Laboratory of Physiology at Oxford, reiterated all the scientific arguments and experimental results reached by his team and others that support this hypothesis. After recalling that visual sensitivity to movement is linked to the magnocellular system and that it helps stabilize the eyes, professor Stein called attention to the alteration of visual-motor functions in dyslexics: instable visual perception, visual congestion, mild left hemineglect, ocular pursuit and vergence movements with abnormal saccadic intrusions, instable binocular fixation, etc. He stressed that cortical control of vergence is largely governed by the magnocellular visual system and that dyslexics have vergence control problems. Finally, as regards a long held controversial link between visual problems and phonological problems prevalent in dyslexics, professor Stein offered a unifying dimension to the magnocellular theory. Magnocellular neurons are in fact widespread throughout the central nervous system, in visual and auditory neural systems, in both sensory and motor systems, within the cerebral cortex, the hippocampus, the cerebellum, and the cerebral stem. It suggests, for example, that visual magnocellular sensitivity determines orthographic aptitude, and auditory magnocellular sensitivity apparently determines phonological aptitude.

The symposium ended with an open discussion led by doctor Christophe Orssaud, from the ophthalmologic department at the Georges Pompidou European Hospital and by Hélène Puech, head scientist at Atol Les Opticiens.
- Are French ophthalmologists adequately informed and aware of the links between visual disorders and dyslexia?
- How can ophthalmologists help dyslexic children?
- Which health professional is best suited to refer patients to phonology or vision specialists – the school doctor, the family doctor, or the pediatrician?
- Orthophonists, whose job it is reeducate dyslexic children, and orthoptists, who help the same children with oculomotor reeducation therapy, are they sufficiently aware of each other’s efforts?

From this discussion emerged a need for closer ties with the research community and for greater continuing education to promote a multidisciplinary approach.

Contacts:
Researcher
Zoï Kapoula
Laboratoire de physiologie de la perception et de l’action
CNRS-Collège de France
Tel: +33 1 44 27 16 35
E-mail: zoi.kapoula@college-de-France.fr
Life sciences department
Françoise Tristani
Tel: +33 1 44 96 40 26
E-mail: francoise.tristani@cnrs-dir.fr

Press contact :
Martine Hasler
Tel : +33 1 44 96 46 35
e-mail : martine.hasler@cnrs-dir.fr