Reading and Writing: An Interdisciplinary Journal 14: 707–755, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Comparing the phonological and double deﬁcit hypotheses for
BRUCE F. PENNINGTON
, CLÁUDIA CARDOSO-MARTINS
PHYLLIS A. GREEN
& DIANNE L. LEFLY
University of Denver, USA;
Universidade Federal de Minas Gerais, Brazil;
Public Schools, USA
Abstract. This study tested the predictions of the phonological and double deﬁcit hypotheses
by experimentally examining speech perception, phoneme awareness, lexical retrieval (serial
and discrete), articulatory speed, and verbal STM in school age child (N = 35) and adoles-
cent (N = 36) dyslexics, and both chronological age (CA) and reading age (RA) controls.
The results conﬁrmed the ﬁndings of previous studies of a deﬁcit in phoneme awareness in
developmental dyslexia. At both age levels, dyslexics performed signiﬁcantly more poorly
than both their CA and RA controls. Although deﬁcits in the other processes investigated,
particularly in rapid serial naming, were also apparent, they were not as clear-cut as the deﬁcit
in phoneme awareness. In general, deﬁnite evidence of a deﬁcit in rapid serial naming was
limited to the more severely impaired dyslexics. Furthermore, although rapid serial naming
contributed independent variation to various literacy skills, its contribution was modest relat-
ive to the contribution of phoneme awareness, regardless of whether the literacy skill relied
more or less heavily on phonological or orthographic coding skills. Further analyses suggested
that variation in rapid serial skill is particularly important for ﬂuent reading of text, whereas
phoneme awareness is particularly important for the development of the ability to read by
phonologically recoding letters or groups of letters in words into their phonological codes.
This explains the relatively strong contribution of phoneme awareness to reading and spelling
ability in general. In sum, the phonological hypothesis offers a more parsimonious account of
the present results than the double deﬁcit hypothesis.
Keywords: Developmental dyslexia, Phoneme awareness, Phonological processes, Rapid
serial naming skill
This study investigates the nature of the underlying cognitive deﬁcit
in developmental dyslexia. In particular, it tests the predictions of two
competing hypotheses (the phonological and the double-deﬁcit hypotheses)
by examining the status of several phonological and lexical retrieval skills in
school-age children and adolescents with reading disability. As argued below,
although there is evidence that both kinds of skills are implicated in alpha-
betic literacy acquisition, numerous questions remain regarding their role in
both normal and impaired reading development.