Multiple stimulus presentation yields larger deficits in children with developmental dyslexia: A study with reading and RAN-type tasks

Abstract

In this study, we examined the effect of multiple versus single stimulus presentation in typically developing readers and children with developmental dyslexia. The tasks involved either reading single words or arrays of words or naming single or multiple colors and digits (rapid automatized naming or RAN). To be able to compare these sets of conditions, we recorded total response times (i.e., the time between stimulus onset and the end of the participant’s vocal response) in all cases. The study included 43 typically developing readers and 25 children with dyslexia.

Results indicate that typically developing readers have a clear advantage with multiple over single items on both RAN and reading tasks. The children with dyslexia showed a moderate advantage for multiple stimuli in naming colors and digits but presented the opposite pattern in reading.

With regard to reading, the disproportionate impairment of the children with dyslexia in dealing with multiple arrays suggests difficulty in integrating the multiple subcomponents of the reading task over and above the basic nuclear deficit in decoding words. Regarding the RAN tasks, results confirm that the requirement of integrating multiple subcomponents may be critical in mediating the predictive value of these measures on reading.

• Reading
• Dyslexia
• RAN
• Vocal RT

This work was supported by grants from the Department of Health and Sapienza University.

Notes

2. ¹In experiments with single stimuli, it is customary to include only trials with correct responses in the computation of time dependent measures. Here, all responses were included to allow for a comparison with multiple-stimulus conditions. However, the general pattern of results did not change much excluding times associated with errors from discrete stimulus trials. As expected, response times on correct trials were usually slightly shorter. For typically developing children, mean reading times changed from 0 to 13 ms depending on the experimental conditions. For children with dyslexia, naming means varied for colors (28 ms faster) but not for digits; reading times became faster by 67 ms for five-letter words and 78 ms for seven-letter words. The size of these changes was considerably smaller than the effects observed comparing single- and multiple-stimulus conditions (see results); therefore, it seems that the differences between discrete and multiple conditions cannot be accounted for by the slowing of error responses.

3. ²By contrast, note that length per se cannot account for the difference between orthographic and nonorthographic materials in children with dyslexia: length (measured in syllables) was the same for five-letter words and digits and color names.