The Double-Deficit Hypothesis
for Decoding Fluency
Sebastian Wren, Ph.D.
In my line of work, I have to travel quite a bit, so you can imagine
how comforting it is to me when I'm told that most of the jets that I
fly on have
the ability to continue to fly even if one engine stops working.
have to say, this is remarkable to me because most of the jets that I
fly only have two engines to start with. The idea that the jet
could continue to work with half of the engines disabled impresses me
tremendously. Of course the jet cannot fly as efficiently or
easily when it loses an engine, but it can fly and -- of much greater
importance to me -- it can land.
I bring this up because it is useful to think about a jet with two engines
when you think about decoding skills. Research suggests that for
most children, there are two engines that drive the development of fluent
decoding skills (Lovett, Steinbach, and Frijters, 2000). For children to develop
good decoding skills, ideally they should have good phonological processing
skills (Engine 1), and they should also be able to process and identify visual
information very rapidly (Engine 2), a process called Rapid Automatic
Naming (Torgesen, Wagner, Rashotte, Burgess, and Hecht, 1997).
Engine 1 -- Phonological Processing Skills
Phonological processing skills have to do with the child's ability to identify
and manipulate sounds within speech. Typically, the assessment of phonological
processing skills that is used is a test of phoneme awareness which measures
the child's ability to segment and manipulate phonemes in speech. For
example, a child may be asked to remove the "LLL" sound in the word "PLAY"
("PAY") or add a "SSS" sound to the beginning of the word "TICK" ("STICK").
The reason this assessment is so important has to do with the fact that
so many children (possibly as many as 40%) do not have good phonological
processing skills when they enter school. Some children, for a variety
of reasons, do not develop an appreciation of what makes words rhyme, and
they have little appreciation for alliteration (words that begin with the
same sounds, such as "Ten Talking Turtles on the Telephone"). The sounds
in speech are not important to these children -- they do not need to know
that the word "SANDWICH" begins with the same sound as "SNOW" to be able
to ask for a sandwich for lunch. Phoneme awareness and indeed phonological
processing skills in general are not important for oral communication, so
young children often pay little or no attention to the sounds in speech before
they come to school. However, they are critically important for reading
and writing (Wagner, Torgesen, and Rashotte, 1994; Gottardo, Stanovich, and
Siegel, 1996; Shankweiler, Crain, Katz, Fowler, Liberman, Brady, Thornton,
Lundquist, Dreyer, Fletcher, Stuebing, Shaywitz, and Shaywitz, 1995)
Engine 2 -- Rapid Automatic Naming (RAN)
The other engine I mentioned earlier -- translating visual information into
a phonological code quickly and easily -- is relatively new in the field of
reading research. This skill is often described as Rapid Automatic Naming
(RAN), and reading researchers do not know very much about it yet. What
we do know is that, just as some children are taller than their peers or
can run faster than their peers, some children are also much faster at identifying
visual information than their peers.
If you ask a group of children to run around the block, you would expect
some children to finish faster than others. Likewise, if you were to
ask a group of children to identify ten pictures of common objects as fast
as they could, you would find that some children are able to identify those
ten objects very quickly while others take a little more time. What is interesting
is that those children who are a little slower to name pictures of objects
also tend to be slower to identify letters of the alphabet or printed words
from a list (Wolf and Bowers, 2000). Without meaning to sound derogatory,
some children are simply slower than other children when it comes to processing
visual information. (As I'll explain later, I am personally in the
Being a little slower to process and identify visual information puts some
students at a slight disadvantage when it comes to reading (Lovett, Steinbach,
and Frijters, 2000). In one second of reading, a fast skilled
reader is able to examine and process about five words in running text.
That translates into about 300 words read per minute by a fast skilled reader.
However a slow skilled reader may only read 230 words per minute -- about
3/4ths of the speed of a fast skilled reader.
That disadvantage is slight, but it is there none-the-less, and this
in speed is more important when children are first learning to read
it is once they become more proficient readers. Children who naturally
process visual information quickly and easily often have an easier time
read than their peers who tend to process visual information more
slowly. And children who process visual information more rapidly
tend to get more out of the time they spend reading than their peers,
and thus have an easier time developing proficient reading skills.
Double Deficit Hypothesis
These two engines, when running full throttle, help children develop decoding
skills quickly and easily with only a little guidance and instruction from
parents and teachers. This is part of the reason why some children
seem to learn to read very easily, while others have more trouble -- some
children have good phonological processing skills and are also able to rapidly
process visual information. Other children either do not have the ability
to process visual information very rapidly, or they lack phonological processing
skills. These children require a little more support from their teachers
when learning to read. Like the jet plane with only one engine, they
can fly, but it may be a little bumpy at first.
But the children who need the most support from their teachers are the ones
who have what is called a "double deficit" -- they come to school lacking
both phonological processing skills and the ability to process visual information
rapidly (Wolf and Greig Bowers (1999). They are the students at greatest
risk of reading failure. In a sense, the cards have been stacked against
them -- they are trying to learn to fly with no engines. And if their teachers
do not intervene and provide a great deal of targeted support as soon as they
come to school in kindergarten, they will rapidly slip behind their peers
and may never learn to read proficiently.
Overcoming and Succeeding
A great deal of research has surfaced over the past 35 years focused on
children who have difficulty processing phonological information and who
consequently are not aware of the phonemes in speech. We know a virtually
everything we need to know now about identifying children who lack phoneme
awareness and teaching children to develop phoneme awareness so they can
develop proficient decoding skills. Unfortunately, less is known about Rapid
Automatic Naming. It is not as easy to identify at a young age, and
even when identified, improving RAN and visual processing speed is considerably
more difficult than helping children develop phoneme awareness.
However, there is still a road to success available, and good teachers
can navigate their students down that road easily (Lovett, Steinbach,
and Frijters, 2000). As I said, it is possible to learn to
fly with one engine, and it is much, much easier to teach children to
be aware of phonemes in speech than it is to make them process visual
information faster. Ensuring that all children develop phoneme
awareness in kindergarten is a good way to ensure that all children
have at least one engine to start with. From there, it may still be
difficult for some children, but with continued support from their
teachers, they can still get off the ground.
A Personal Story
As I mentioned earlier, I am a slow reader. The last time I was tested
objectively (when I was an undergraduate in college) the Nelson-Denny indicated
that my comprehension scores were in the 99th percentile, but my reading rate
was in the 3rd percentile. I read fast enough to comprehend well, but
nowhere nearly as fast as my peers. Apparently, I learned to fly with
just one engine -- because of some good instruction early in my life, I learned
to read proficiently enough to make it through college and graduate school
even though I read very slowly. Exactly the same thing can be said
of my brother, a national merit finalist in high school. And my father,
a geophysicist. These things tend to run in families, and in my family,
most of us are very slow readers.
Fifteen years have passed since the Nelson-Denny revealed that my reading
rate is in the 3rd percentile, and I would not be at all surprised to find
that my reading rate has increased over the years. Since college, especially
in graduate school, I developed the habit of reading between 4 and 6 hours
a day. I have no data, but I am sure that all of that practice has increased
my reading rate substantially. It is not easy to affect Rapid Automatic
Naming, but if anything is going to do it, practice has got to be the answer.
Because of my reading habits, I process between sixteen million and twenty-four
million words a year. To put that in perspective, one year is equal
to 31.4 million seconds, so I read about one word for every two seconds of
Of course, I must confess that not all of the reading that I do every day
is challenging, technical text. The most recent book I read cover-to-cover
was "Harry Potter and the Order of the Phoenix." And while my current
bedtime reading may seem more challenging (Sally Shaywitz's book, "Overcoming
Dyslexia"), I assure you that for me, it is not. I am so familiar with
research literature in the area of reading acquisition that Shaywitz's book
is easy reading for me.
In other words, while I read a lot more than most of my peers, most of the
reading that I do is for pleasure, and most of it does not really stretch
the boundaries of my reading comprehension skills. For children who are slow
readers, that is the formula for success -- they must read much, much more
than their faster peers, and one good way to encourage them to do that is
to encourage them to spend a lot of time reading easy text for pleasure (see
V is for Volume).
Speaking from personal experience, I would say that reading may come easier
to other people, and other people may be able to read faster than I do, but
for a slow reader who had a little difficulty getting off the ground with
one good engine, nobody enjoys reading more than I do.
Gottardo, A., Stanovich, K. & Siegel, L. (1996). The relationships between
phonological sensitivity, syntactic processing and verbal working memory in
the reading performances of third-grade children. Journal of Experimental
Child Psychology, 63: 563-582.
Lovett, M. W., Steinbach, K. A., & Frijters, J. C. (2000). Remediating
the Core Deficits of Developmental Reading Disability: A Double-Deficit Perspective.
(Journal of Learning Disabilities, 33(4), 334-358.)
Shankweiler, D., Crain, S., Katz, L., Fowler, A., Liberman, A., Brady, S.,
Thornton, R., Lundquist, E., Dreyer, L., Fletcher, J., Stuebing, K., Shaywitz,
S. & Shaywitz, B. (1995). Cognitive profiles of reading-disabled children:
Comparison of language skills in phonology, morphology and syntax. Psychological
Science, 6: 149-156.
Torgesen, J.K., Wagner, R.K., Rashotte, C.A., Burgess, S.R. and Hecht, S.A.
(1997). The contributions of phonological awareness and rapid automatic naming
ability to the growth of word reading skills in second to fifth grade children.
Scientific Studies of Reading, 1, 161-185.
Wagner, R., Torgesen, J. & Rashotte, C. (1994). Development of reading-related
phonological processing abilities: New evidence of bidirectional causality
from a latent variable longitudinal study. Developmental Psychology, 30: 73-87.
Wolf M, & Greig Bowers P. (1999). The double-deficit hypothesis for
the developmental dyslexias. Journal of Educational Psychology, 91: 415-438.
Wolf, M. & Bowers, P. (2000). The question of naming-speed deficits
in developmental reading disability: An introduction to the Double-Deficit
Hypothesis. Journal of Learning Disabilities, 33, p. 322-324. (Special Issue
on the Double-Deficit Hypothesis; Special Issue Editors: M. Wolf & P.
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