Abstract: As to the origin and mechanisms of developmental dyslexia, nonlinguistic framework proposes that the phonological and other deficits at the linguistic level may stem from more fundamental deficits in sensory information processing, including acoustic-auditory and auditory temporal processing and visual perceptual processing. Previous studies have shown that visual perceptual deficits of dyslexic children may stem from the deficit in processing more basic visual attributes, as basic visual features are fundamental to higher-level visual processing. Perceptual learning is the improvement of perceptual performance as a function of training (Gibson, 1969), which has been found in various visual tasks involving basic visual features. Here, using visual searching tasks, the main purpose of the present study was to investigate to what extent dyslexic children would show deficits in perceptual processing and learning and whether these deficits are related to their performance in linguistic tasks. Eighteen participants, 9 with dyslexia, 9 chronological age- and nonverbal IQ-matched control children, were screened from a large pool of students in 3, 4, 5 grades with the standardized Chinese written vocabulary test, the reading fluency test and the Raven’s Standard Progressive Matrices test. We tested 9 children in dyslexia group and 9 age-matched children in control group with a parallel search task, a serial search task and a serial search task in restricted time. Study 1 utilized a parallel searching task to examine whether there is a deficit in the basic searching processing and learning in dyslexia group. Study 2 used a serial searching task to explore whether there is a deficit in more complex searching processing and learning. Study 3 adopted a serial searching task with restricted time to investigate whether the ability of serial searching processing will be affected by the restricted time. The results showed that there was no difference between dyslexics and control children in parallel searching task, however, children with dyslexia had significantly longer reaction time than normal children to retrieve the target stimuli in serial searching processing. In addition, the searching accuracy was significantly lower for children with dyslexia than for control group in serial searching task with restricted time. Moreover, the searching accuracy in the serial searching task with restricted time was significantly correlated with the performance of the standardized written vocabulary test. These results showed that Chinese developmental dyslexia has deficits in perceptual processing and learning in serial searching process, suggesting that the deficits may underlie the development of Chinese reading skill to some extent.

Key words: developmental dyslexia, perceptual learning, visual search