Revisiting Strephosymbolie: The Connection between Interhemispheric Transfer and Developmental Dyslexia

Abstract

The hypothesis that an atypical hemispheric specialization is associated to developmental dyslexia (DD) is receiving renewed interest, lending some support to Orton’s theory. In this article, we investigated whether interhemispheric transfer processes (IHT) are likely to be involved in developmental dyslexia. In this study, we tested 13 children with developmental dyslexia and 13 matched controls (aged 8 to 13 years) in four different tasks. In a tactile transfer task, the dyslexic children’s performance was less accurate. In a standard Poffenberger paradigm, dyslexic children performed slower than the controls in all conditions and did not show any difference between crossed and uncrossed conditions. Furthermore, they showed an increased asymmetry of performance according to the responding hand, while controls gave more coherent responses. In a visual task of object orientation discrimination, dyslexic children had slower Response Times (RTs) than controls, especially for mirror-reversed objects in the right visual field. Finally, a higher number of dyslexic children showed mirror-drawing or mirror-writing with respect to controls. Our results as a whole show that children with DD are impaired in interhemispheric transfer, although the differences in performance among dyslexic individuals suggest the impairment of different psychophysiological mechanisms. As such, a common origin in terms of connectivity problems is proposed.

Keywords: crossed-uncrossed difference paradigm; developmental dyslexia; interhemispheric transfer; mirror writing.

Figure 1

Three paradigms: (A) interhemispheric transfer of tactile information; (B) interhemispheric transfer of visual information (crossed-uncrossed differences, CUD); (C) same-different orientation judgment task.

Figure 2

Results of the interhemispheric transfer of tactile information task.

Figure 3

Results of the interhemispheric transfer of visual information task for each experimental group, response hand condition, and visual field condition. (the line between squares indicates participants with DD and the line between diamonds indicates control participants).

Figure 4

Results of the interhemispheric transfer of visual information task in terms of frequencies within the two children groups of positive CUDs.

Figure 5

Mean response times of the orientation judgment task for the two children groups (dyslexic participants in red and controls in blue), the three visual field conditions (A: left, B: right, AB: bilateral) and the three stimulus conditions (mirror, inverted and same, respectively).

Figure 6

Results of the writing task in the two groups in terms of frequency of letter inversions.