Coherent motion and coherent form perception in developmental dyslexia

The role of visual perception in Developmental Dyslexia (DD) is still controversial. Although the Magnocellular theory of DD has been widely criticized, it is still unclear if the deficit in motion perception is specific for the Magnocellular system or if it is connected to a general difficulty in discriminating signal to noise. The aim of this study is to investigate dorsal and ventral pathways in different conditions of noise in a population of DD. Seventeen DD and forty-three typically developed (TD) children (age 7-12 years) participated in the study. All the subjects performed the Motion coherence test and the Form coherence test. In the motion coherence test the ability in discriminating the direction of luminance coherent moving dots in different levels of noise is reported. The Form test measures the ability in form recognition in different condition of noise. The MANOVA showed that DD differed from TD both in the Motion and in the Form coherence tests. Moreover, these differences are significant only in intermediate noise conditions. These results are in accordance with the noise exclusion theory of DD and added important information about the DD deficit in discriminating signal to noise.