SD-Squared Revisited: Reply to Coltheart, Tree, and Saunders (2010)

Anna M. Woollams, Matthew A. Lambon Ralph, David C. Plaut, Karalyn Patterson

    Research output: Contribution to journalArticlepeer-review

    100 Downloads (Pure)


    The connectionist triangle model of reading aloud proposes that semantic activation of phonology is particularly important for correct pronunciation of low-frequency exception words. Our consideration of this issue (Woollams, Lambon Ralph, Plaut, & Patterson, 2007) reported computational simulations demonstrating that reduction and disruption of this semantic activation resulted in the marked deficit in low-frequency exception word reading that is characteristic of surface dyslexia. We then presented 100 observations of reading aloud from 51 patients with semantic dementia (SD) demonstrating a universal decline into surface dyslexia, a phenomenon we termed "SD-squared." Coltheart, Tree, and Saunders (2010) have more recently provided a simulation of the SD-squared data within the dual route cascaded (DRC) model, achieved by varying the amount of damage to components of the lexical and nonlexical pathways. Although they suggested that these simulations provide a closer fit to the SD patients' reading data than our own, we demonstrate here that this is not the case. Moreover, we argue that the connectionist triangle model account has substantially greater explanatory and predictive power than the DRC account. © 2010 American Psychological Association.
    Original languageEnglish
    Pages (from-to)273-281
    Number of pages8
    JournalPsychological Review
    Issue number1
    Publication statusPublished - Jan 2010


    • frequency
    • reading aloud
    • regularity
    • semantic memory
    • surface dyslexia


    Dive into the research topics of 'SD-Squared Revisited: Reply to Coltheart, Tree, and Saunders (2010)'. Together they form a unique fingerprint.

    Cite this