The Cognitive And Neural Basis Of Impaired Visual-spatial Attention Shifting In Chinese Dyslexic Children

Developmental dyslexia is one of the most common learning disorders in children and adolescents.Revealing the causes of dyslexia is necessary for the intervention of this disorder.It has been shown that inefficient attentional shifting is likely a causal factor for reading difficulties in dyslexics.The process of attentional shifting is characterized by an early facilitation effect,resulting from the successful engagement of attention,and a later inhibitory effect—frequently referred to as inhibition of return(IOR)—which encourages attentional disengagement and facilitates efficient visual sampling.However,a fundamental question that the process in which the attentional dysfunction occurs in dyslexics remains unclear.And further,the neural basis of this attentional shifting impairment also remains unclear.The first study examined the time course of attentional shifting in dyslexic and typically developing children,by parametrically manipulating the cue-target onset asynchronies(CTOAs)in a spatial cueing task.Experiment 1 revealed an early facilitation effect in dyslexic children,suggesting that they have no issue in engaging attention to salient spatial locations.However,contrast to both age-matched and reading level-matched healthy controls,no reliable IOR effect was observed in dyslexic children,suggesting that they have difficulties in disengaging attention.When a second cue was presented to encourage attentional disengagement in Experiment 2,reliable IOR effects were observed in the same group of dyslexic children and importantly,the onset time of IOR was comparable to that in healthy controls.These results clearly show a selective impairment of attentional disengagement in dyslexic children and provide a solid empirical basis for intervention programs focusing on attentional shifting.To explore the neural basis of such an IOR impairment in dyslexic children,the second study examined the electrophysiological responses during the attentional shifting processing for both dyslexic children and typical developing children by recording the Event-Related Potentials(ERPs).Using the Topographic Analysis of Variance(TANOVA),the difference between different validity conditions(valid cue condition vs.invalid cue condition)in dyslexic was weaker than that in normal children in the early time window.More interestingly,the effect occurred earlier and lasted longer when the cue-target onset asynchronies(CTOA)was increased for dyslexic children.These results indicate that the sluggish attentional disengagement in dyslexic children was derived from the difficulties in discriminating congruent and incongruent conditions in the early time point.Taken together,these studies provide strong evidence for understanding the cognitive and neural basis of the impaired visual spatial attentional shifting in developmental dyslexia.Most importantly,it also gives guidance for the intervention and assessment of dyslexic children.