Phonological dyslexia and phonological impairment: an exception to the rule?

The condition known as phonological dyslexia involves very poor reading of non-words, with otherwise good word reading performance [e.g. Derouesné & Beauvois, 1979; Sartori, G., Barry, C., & Job, R. (1984). Phonological dyslexia: A review. In R. N. Malatesha & H. A. Whitaker (Eds.), Dyslexia: A global issue. The Hague: Martinus Nijhoff Publishers]. Theoretical accounts of this non-word reading impairment suggest disruption to either a component of a non-lexical orthographic-phonological reading route [that is specifically involved in reading non-words; Coltheart, M., Rastle, K., Perry, C., Langdon, R., & Zeigler, J. (2001). A dual route cascaded model of visual word recognition and reading aloud. Psychological Review, 108, 204-256] or to generalised phonological processes on which novel reading is heavily dependent [Farah, M., Stowe, R. M., & Levinson, K. L. (1996). Phonological dyslexia: Loss of a reading-specific component of cognitive architecture? Cognitive Neuropsychology, 13, 849-868; Harm, M. W., & Seidenberg, M. S. (1999). Phonology, reading acquisition, and dyslexia: Insights from connectionist models. Psychological Review, 106, 491-528]. The present paper questions the latter hypothesis: that phonological dyslexia always occurs in connection with some other form of phonologically based disruption (i.e. in a 'cluster' of impairments that are not necessarily reading-specific). Contrary to this view, several recent studies have reported that phonological dyslexia can occur without corresponding generalised phonological impairment [e.g. Caccappolo-van Vliet, E., Miozzo, M., & Stern, Y. (2004a). Phonological dyslexia without phonological impairment? Cognitive Neuropsychology, 21, 820-839; Caccappollo-van Vliet, E., Miozzo, M., & Stern, Y. (2004b). Phonological dyslexia: A test case for reading models. Psychological Science, 15, 583-590]. However, the work is subject to a number of criticisms. The following study examines performance of a phonological dyslexic case (JH) on a variety of phonological based tasks and, unlike many other studies, components of phonological short-term memory. Despite clear impairments in reading non-words, good performance on a variety of phonological tasks makes the possibility of generalised phonologically based disruption unlikely. The view that JH's good phonological skill was dependent on the use of spelling based strategies was also excluded. As a result, JH's pattern of performance provides clear evidence that phonological dyslexia can occur without any generalised phonological impairment.