The Dyslexia Project - Analysis of behavior and eye movements in children with dyslexia
Project Completed
This was a collaboration with Susanne Trauzettel-Klosinski, MD, and her colleagues at the University Eye Clinic in Tübingen, Germany.
Project A
We measured the speed of pictogram naming and text reading in dyslexic and normally reading children. The relationship between these two fundamental mechanisms was investigated to clarify the role of pictogram naming in the genesis of dyslexia.
Bottom line: Some Dyslexic children can be very fast pictogram namers and still be profoundly dyslexic.
Publication:
Trauzettel-Klosinski S, MacKeben M, Reinhard J, Feucht A, Dürwächter U & Klosinski G. (2002) Pictogram naming in dyslexic and normal children assessed by SLO. Vision Research 42 (2002), 789-799. (pubmed)
Abstract
We measured pictogram naming (PN) and text reading in dyslexic and normally reading young teenagers. Eye movements were monitored by Scanning Laser Ophthalmoscope, revealing positions of fovea, stimuli on the retina, and speech simultaneously. While text reading speed showed the expected difference between groups, PN speeds overlapped widely. PN was mainly controlled by retrieval time in both groups and correlated with age in dyslexics. We conclude that PN activates visual/eidetic mechanisms that are distinct from the phonemic/analytic pathway necessary for reading. This dual organization leads to wide range of combinations of performances in PN and text reading.
Project B
We used a Scanning Laser Ophthalmoscope to analyze the eye movements of dyslexic and normally reading children while reading single words of variable length. Bottom line: Dyslexics can perform instantaneous adjustment of reading saccade parameters dependent on word length, but with lower gain than the normally reading children.
Publication:
MacKeben M, Trauzettel-Klosinski S, Reinhard J, Dürrwächter U, Adler M & Klosinski G (2004). Eye movement control during single word reading in dyslexics. Journal of Vision, Vol. 4, No. 5, Art. 4, pp. 388-402; http://www.journalofvision.org/4/5/4/ (free open access)
Abstract
We investigated whether dyslexics make instantaneous automatic adjustments of reading saccades depending on word length. We used a single-word reading paradigm on 10 dyslexic and 12 normally reading children aged 11-15 years. Eye movements were recorded by scanning laser ophthalmoscope (SLO) while subjects read single words of different length aloud. All subjects passed standardized prescreening tests, which included a reading test, to exclude those with discernible deficits of eyesight, oculomotor skill, or intellectual development. We measured number, direction, frequency, and amplitude of saccades, as well as the durations of inter-saccadic intervals, as functions of word length. The results show that word length influences the number and amplitude of reading saccades in both subject groups, but this relationship showed quantitatively significant group-specific differences: Both groups showed a gradual increase of the saccade amplitudes in either direction dependent on word length, but the gain of this function was significantly lower in the dyslexics. The durations of holding phases between saccades were significantly longer in the dyslexics, and accordingly, we found a lower rate of occurrence of saccades per unit time in the dyslexics. Forward saccade amplitudes showed no correlation with the duration of the preceding or following holding phases in either group. The data show that the mechanisms enabling dyslexics to make instantaneous adjustments of reading saccades depending on word length are present but quantitatively impaired. This supports the view that these adjustments may help dyslexics to increase reading speed, but that they cannot utilize them to the same extent as normal readers.