Comments on the Dyslexia and Visual Attention Study

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By Hugh W. Catts, Ph.D

Research AlertA recent study from the University of Padua, in Italy, argues that problems in visual attention may underline the difficulties that children with dyslexia have in learning to read.  The researchers administered measures of visual spatial attention, speech-sound processing, and rapid color naming to kindergarten children (age 5, prior to formal reading instruction), and followed them for two years as they learned to read. Good and poor readers were identified in first and second grades.

The results showed that children’s performance on visual spatial attention measured in kindergarten uniquely predicted their reading abilities in first and second grades.

The authors concluded that, “these findings virtually close not only a long-lasting debate on the causal role of visual spatial attention deficits in dyslexia but also open the way to a new approach for early identification and more efficient prevention of dyslexia.”

How do these results fit with what is known about dyslexia?

Whereas the results of this study are quite interesting from a scientific perspective, they should be interpreted in the context of what is known about dyslexia.

The preponderance of the evidence on dyslexia indicates that language problems, especially speech-sound (phonological) processing deficits underlie the difficulties that most children with dyslexia experience in learning to read.  Research also demonstrates that early intervention involving speech-sound processing and emergent literacy skills can significantly improve the reading outcomes of children with dyslexia.

The reported study argues that visual deficits also play a causal role in dyslexia, but its conclusions are very premature and go well beyond what can reasonably be inferred from the findings.

Is this work not consistent with other studies showing that individuals with dyslexia may have visual problems?

Yes, there is now converging evidence that some individuals with dyslexia have problems in visual processing. Both behavioral and neurophysiological evidence has shown a connection between dyslexia and problems in a major visual pathway in the central nervous system that is involved in sequencing, visual motor control, and other aspects of vision.  The authors of the current paper believe that it is problems in this pathway that may be related to the deficits that they report in visual spatial attention.

Most of the work on visual deficits in dyslexia has involved individuals who already have reading disabilities. As such, some have argued that reading problems themselves may cause poor performance on visual measures.  The current study is particularly significant in that it examined kindergarten children (pre-readers in Italian schools) who later developed dyslexia.  Thus, visual problems were present before reading difficulties and could not be explained by these difficulties.

While visual problems may precede reading difficulties in dyslexia, they do not necessarily play a causal role in these difficulties, as stated so strongly by the authors. As we know, correlation does not mean causation, even a predictive correlation. To demonstrate a causal basis for visual attention deficits requires additional studies that manipulate visual attention (by intervention, see below) and observe changes in learning to read.

So, on the basis of the current study, it seems very premature to say the door is closed on the debate concerning the causal role of visual attention deficits in dyslexia.

What other contributions are made by this study?

Only a limited number of longitudinal studies have examined visual and speech-sound processing/rapid naming deficits at the same time. The current study is one of the first to show that visual attention deficits predict reading outcomes over and above speech-sound processing and rapid naming.

Some caution should be taken, however, in drawing conclusions from these results. The correlations observed between visual attention and later reading are comparable to (or higher than) those reported for visual abilities in a large review of the literature by the National Early Literacy Panel.  However, the correlations found for speech-sound processing and rapid naming are much lower than those reported by the same panel. Thus, results will need to be replicated, perhaps using other measures of speech-sound processing/rapid naming that could be more highly related to reading.

What are the implications of these results for early identification?

The authors argue that screening for visual attention problems could be an effective approach for the early identification of dyslexia. However, based on the results presented, it is very unlikely that such a screening procedure would identify children with dyslexia with an acceptable level of accuracy.

First, the reported correlations between visual attention and later reading abilities were much lower than what is necessary for a single measure to be an accurate predictor. Furthermore, the results show that only slightly more than half of the children who became poor readers had visual attention deficits as kindergarteners. Also, it appears from the data presented that many good readers had visual problems in kindergarten as well.

These results are not surprising because a large body of research on the early identification of dyslexia has shown that no single measure is likely to be accurate in identifying dyslexia in pre-reading children. It appears that a combination of variables like family history, early language development, phonological awareness, emergent literacy, and perhaps visual abilities will be necessary to accurately identify dyslexia prior to formal reading instruction.

What are the implications for intervention?

The authors further state that children at risk for dyslexia (those with poor visual attention) “could be treated with preventive remediation programs of visual spatial attention before they learn to read.” They go on to cite a small number of studies that have used “action videos” to improve attention abilities and reading.

Whereas such an approach is novel and of scientific interest, the evidence to support it is presently quite weak.  By no means should we alter our recommendations for intervention based on these preliminary findings.  Stronger and more converging evidence is necessary before we move away from what we know works to a novel intervention. Readers should be cautious of attempts to take advantage of the research on visual attention to promote unsupported visual training programs for dyslexia.

Hugh W. Catts, Ph.D., Professor and Chair, Department of Speech-Language-Hearing: Sciences & Disorders, University of Kansas; Co-Director, Intercampus Program in Communicative Disorders, University of Kansas; Past President of the Society for the Scientific Study of Reading; Past Chair of the Research Committee and Scientific Advisory Board Member of the International Dyslexia Association.

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