NEUROSCIENCE
Published: 19 May 2020
doi: 10.3389/frym.2020.00061
WHY DO SOME CHILDREN STRUGGLE TO READ?
Eva Kimel 1* and Merav Ahissar 1,2
1
Edmond & Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
2
Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel
YOUNG REVIEWERS:
HAKFAR
HAYAROK
AGES: 12–13
Some children have a very hard time learning to read. In spite of
normal intelligence and no special hearing or vision problems, they
still read very slowly and with many errors. These problems persist
even after they become adults: their reading improves with practice
but less than that of their peers. This persistent reading difficulty
is called developmental dyslexia. It is still not clear what causes
dyslexia, and in this article we describe findings from our lab and
our interpretation regarding the basis of dyslexia. We found that
people with dyslexia benefit less than people without dyslexia from
repetition of sounds, and that they behave as if they are less familiar
with common syllables and word structures. Using brain scanning
equipment, we also found that brains of people with dyslexia “forget”
sounds faster. This might be the reason that they do not benefit from
repetition as much as people without dyslexia.
LEARNING TO READ
Reading is the process of translating written symbols (such as English
letters) into a series of sounds, which are meaningful words. When
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children first start to read, they need to use sequential deciphering
of letters to sounds in order to read words, but after they get some
experience, they begin to identify complete words [1]. Representations
of verbal words and their meaning exist in children’s minds even before
they start reading. We know this because children can understand
spoken language and speak, long before they learn to read. Most
children learn to read at the age of 6–7, but this skill keeps improving
and becoming more efficient as children get older.
READING CAN BE A CONTINUOUS STRUGGLE
For some children, learning to read is not simple and can even be very
frustrating. About 7% of the kids in regular schools have a very hard
time learning to read, even though they do not have special vision
or hearing problems and have normal intelligence. These children
are born with this difficulty and it will stick with them even when
they become adults. This difficulty with reading is a learning disability
called developmental dyslexia. People with developmental dyslexia
read slower and with more errors than people without dyslexia do.
Usually, people with dyslexia also make lots of spelling mistakes, but
other than problems with reading and spelling, their abilities in other
areas (such as mathematics) are usually perfectly normal (unless they
have another disorder). Dyslexia was first described about 100 years
ago and since then researchers have been trying to understand how
dyslexia causes difficulty acquiring reading skills.
Reading is a complex process that involves vision, hearing, memory,
and eye movements. Given that all these are undamaged in people
with dyslexia, it is peculiar that they still have such difficulty
with reading. It seems that despite the specific characterization
of dyslexia, people with dyslexia have additional difficulties, which
deviate from reading and writing, and even from the boundaries of
language usage.
When learning to read (or reading unfamiliar words) we combine the
sounds that the letters represent into a word. When we are required
to write a word that we hear, we break it down to speech sounds
and translate them to letters. The basic speech sounds are called
phonemes. Since people with dyslexia experience difficulties with
the process of separating and joining phonemes, many researchers
hypothesized that the mental representation of basic language sounds
is impaired in dyslexia. About 40 years ago, researchers suggested that
the difficulty in dyslexia lies in the ability to process sounds, and is not
specific to language [2]. Our experiments were designed to understand
this concept more fully.
OUR HYPOTHESIS: DYSLEXIA INVOLVES FASTER
“FORGETTING” OF PRIOR KNOWLEDGE
In the last 15 years we conducted a series of experiments with children,
adolescents, and adults with dyslexia. A typical experiment is made
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fMRI (FUNCTIONAL
MAGNETIC
RESONANCE
IMAGING) SCANNER
A device using
magnetic fields to
measure brain activity
when the participant is
performing different
tasks. The
measurement is based
on the amount of
oxygen in the blood
flowing in the brain
during the task. During
the experiment, the
participant lies inside a
tube-like structure and
performs the required
task, while the oxygen
levels are measured.
The measurement is
non-invasive and that is
why it is very common
in the field
of neuroscience.
CORTEX
A part of the brain, its
outer layer. The cortex
processes auditory
(sound) and visual
information, deals with
problem solving,
sending movement
messages to the
muscles and much
more. The cortex is
folded, and thus is full
of ridges and grooves,
which greatly enlarge
its surface area. The
cortex is divided into a
few sub-areas
according to the
grooves, and these
sub-areas are related to
different functions.
Developmental Dyslexia
from some tens of “steps.” In each step, the participant hears two
sounds with a short time gap (about a second) between them. The
participant is asked to decide which sound had a higher pitch, the first
or the second. In experiments of this type, participants feel that they
are comparing the two sounds, and that is how they decide. However,
it turns out that sounds from previous steps also influence the decision:
our internal representation of the pitch of the first sound in the current
step becomes similar to previous sounds we heard, in previous steps.
For example, if we hear a sound with a high pitch now, but most of
the previous sounds were with low pitch, our representation of this
sound will be a bit lower, it will be “pulled down.” We discovered that
this effect is smaller for participants with dyslexia [3]. Following this, we
hypothesized that people with dyslexia have difficulty with accurately
storing the sounds that they hear in memory. Such storing is essential
for efficient reading.
In order to test the hypothesis that sound memories decay faster in
the brain of people with dyslexia, and to understand in which brain
areas this faster decay occurs, we conducted another experiment.
In this experiment, participants were scanned in a device called a
functional magnetic resonance imaging scanner (fMRI scanner) while
performing the same task of listening to sounds and determining
which has a higher pitch. The fMRI allowed us to record the activity
of the participants’ brain during the experiment.
Generally, when the same sound is presented twice with a short gap
in between, the brain’s response to the second presentation is smaller.
This phenomenon is called neural adaptation. The smaller response to
the second sound tells us that the brain still remembers the first sound
in some way, because the first sound still influences the processing of
the second sound. In people with dyslexia, we found that this period
of subconscious memory of the first sound was shorter. When the
gap between sounds was 10 s, the response to the second sound
measured in the brains of people without dyslexia was smaller, telling
us that the memory of the first sound was still stored in their brains.
In contrast, people with dyslexia had a full-intensity response for the
second sound if the sounds were 10 s apart, telling us that their brains
no longer had available memory of the first sound. This difference
in memory duration was observed in multiple areas of the cortex [4]
(Figure 1).
PEOPLE WITH DYSLEXIA LEARN MORE SLOWLY FROM
REPETITION
The main problem faced by most people with dyslexia is reading
words. How is this problem related to the difficulty we discovered
with memory of sounds? It is possible that for people with dyslexia,
the fast memory decay makes the accumulation of knowledge slower.
Figure 2 illustrates this idea. Generally, the more we are exposed to
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Figure 1
People with dyslexia
have a faster decay of
sound memories than
people without
dyslexia. The right and
left sides of the brain’s
cortex are shown for
readers without
dyslexia (top row) and
readers with dyslexia
(bottom row). The
human cortex is folded,
and thus, in order to
see the neural activity
taking place at the
depth of the folds, the
folds in this figure were
“straightened”
outwards and it looks
as though the brain is
smooth, and the folds
appear in dark gray.
The colors represent
the length of time that
sound memories last in
the brain (see scale on
the left). You can see
that the brains of
readers without
dyslexia have more
yellow in many areas of
the cortex, meaning
that memories lasted
longer in the brains of
these people than in
the brains of those with
dyslexia. This difference
was particularly strong
in a relatively small area
which is related to
auditory processing
(marked with a red
contour), probably
because that area is
strongly involved in the
task that the
participants performed
(deciding which sound
has a higher pitch).
MORPHOLOGY
The branch of language
research that studies
the structure and
components of words
and how components
are combined into
whole words.
Figure 1
something, the more we improve our performance in tasks related
to this exposure. But, for people with dyslexia, the learning curve
for things they were previously exposed to is slower. Examining the
differences in performance between the two groups in Figure 2 shows
that although people with dyslexia continue to learn with repeated
exposure, the difference between the performance of the two groups
will become bigger as the amount of exposure increases.
EFFECTS ON LANGUAGE SKILLS: PEOPLE WITH DYSLEXIA
BENEFIT LESS FROM WORD AND SYLLABLE FAMILIARITY
THAN PEOPLE WITHOUT DYSLEXIA
We use language throughout our lives, and most of us learn the rules
and structure of language automatically and subconsciously. In our
experiments, we used the structure of language and the rules about
how word parts are put together, which is called morphology, to study
differences between people with dyslexia and people without it.
In Hebrew, all verbs have one of a few specific structures, and every
other form is “illegal” in the language, so readers are never exposed
to those non-existing forms. For example, the word lagadnu is not
a real word in Hebrew, but it is very similar in structure to the real
words katavnu, pagashnu, and kalatnu. On the other hand, the word
hukshimti is also not a real word in Hebrew but, unlike lagadnu, there
are no Hebrew words that share its structure, so it is less familiar to
native Hebrew readers.
We examined whether reading speed is influenced by familiarity
with word morphology. Students without dyslexia read made-up
words that had a structure that was similar to that of real words
faster and more accurately than they read words without a familiar
structure. This is to be expected, because words with familiar structure
require less “work” from the brain—they do not have to be processed
letter-by-letter. However, for students with dyslexia, there was no
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Figure 2
Learning from previous
exposure. An
illustration of learning
curves of people with
and without dyslexia
according to the
amount of exposure to
stimuli (such as
syllables or words).
Both for people with
and for people without
dyslexia, larger
exposure results in
more reliable internal
representations and
subsequently better
performance. However,
we hypothesize that
the learning curve of
people with dyslexia is
slower, meaning that as
exposure increases, the
difference in
performance between
the groups increases
as well.
Figure 2
significant improvement in speed or accuracy of reading made-up
words with Hebrew morphology compared with words that had no
familiar structure [5]. These results tell us that morphology does not
assist people with dyslexia in reading as much as it assists people
without dyslexia.
When we used units that are smaller than words, we found similar
results. Words are constructed from syllables. The word grandfather,
for example, is constructed from three syllables: grand-fa-ther. The
syllable ther is frequent in English, it appears in many words. In
contrast, there are non-frequent syllables, such as lus (the third
syllabus in the word stimulus). It is known that syllable frequency
has a big effect on the success rate when participants are asked to
repeat series of syllables that were presented to them. In accordance
with this, in our experiment participants repeated series of frequent
syllables more accurately than series of less frequent syllables,
but this advantage of syllable frequency was significantly smaller
for participants with dyslexia [6]. These results tell us that syllable
frequency does not enhance the memory of people with dyslexia
as much as it enhances the memory of people without dyslexia.
Thus, people with dyslexia have a reduced benefit from repetition of
syllables and of word structures, similarly to their reduced benefit from
repetition of simple sounds, and subsequently their performance is not
as good as of people without dyslexia. The exposure of participants
with dyslexia to syllables and words is similar to the exposure of
participants without dyslexia, but participants with dyslexia gain less
from this long-term exposure, as illustrated in Figure 2.
SUMMARY
Developmental dyslexia is a specific learning disorder which hinders
the acquisition of reading skills. Researchers have been searching for
the cause of dyslexia for many years, and in this article we suggest that
the main difficulty in dyslexia is less efficient usage of prior knowledge
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about stimuli that were already presented, due to a faster decay of
memory for these stimuli. We based this idea on results of experiments
with simple sounds and brain activity. We also compared the accuracy
and speed of reading words with and without a familiar structure,
and the memory of frequent vs. infrequent syllables. These data help
us to understand the cause of dyslexia, and an understanding of the
cause might eventually help with treatment. Although dyslexia persists
throughout a person’s life, interventions can improve the abilities of
people with dyslexia and, in general, the earlier the interventions take
place, the more effective they are.
ORIGINAL SOURCE ARTICLE
Jaffe-Dax, S., Kimel, E., and Ahissar, M. (2018). Shorter cortical
adaptation in dyslexia is broadly distributed in the superior temporal
lobe and includes the primary auditory cortex. eLife 7:1–9. doi: 10.
7554/eLife.30018
REFERENCES
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2. Tallal, P. 1980. Auditory temporal perception, phonics, and reading disabilities in
children. Brain Lang. 9:182–98. doi: 10.1016/0093-934X(80)90139-X
3. Jaffe-Dax, S., Raviv, O., Jacoby, N., Loewenstein, Y., and Ahissar, M. 2015. A
computational model of implicit memory captures dyslexics’ perceptual deficits.
J. Neurosci. 35:12116–26. doi: 10.1523/JNEUROSCI.1302-15.2015
4. Jaffe-Dax, S., Kimel, E., and Ahissar, M. 2018. Shorter cortical adaptation in
dyslexia is broadly distributed in the superior temporal lobe and includes the
primary auditory cortex. ELife 7:e30018. doi: 10.7554/eLife.30018
5. Kimel, E., and Ahissar, M. 2019. Benefits from morphological regularities in
dyslexia are task dependent. J. Exp. Psychol. Learn. Mem. Cogn. 46:155–69.
doi: 10.1037/xlm0000717
6. Kimel, E., Weiss, A. H., Jakoby, H., Daikhin, L., and Ahissar, M. 2019. Spans
attributed to short-term memory are explained by sensitivity to long-term
statistics in both musicians and individuals with dyslexia. bioXriv.
doi: 10.1101/795385
SUBMITTED: 22 March 2020; ACCEPTED: 03 April 2020;
PUBLISHED ONLINE: 19 May 2020.
EDITED BY: Idan Segev, Hebrew University of Jerusalem, Israel
CITATION: Kimel E and Ahissar M (2020) Why Do Some Children Struggle to Read?
Front. Young Minds 8:61. doi: 10.3389/frym.2020.00061
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CONFLICT OF INTEREST: The authors declare that the research was conducted in
the absence of any commercial or financial relationships that could be construed
as a potential conflict of interest.
COPYRIGHT © 2020 Kimel and Ahissar. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is permitted, provided the original
author(s) and the copyright owner(s) are credited and that the original publication
in this journal is cited, in accordance with accepted academic practice. No use,
distribution or reproduction is permitted which does not comply with these terms.
YOUNG REVIEWERS
HAKFAR HAYAROK, AGES: 12–13
We are seventh grade gifted students class at Hakfar Hayarok—Youth village for
environmental leadership. We study with students with shared interests, enrich our
knowledge in various and diverse fields, we are exposed to content in science and
the humanities and enjoy very high level of learning.
AUTHORS
EVA KIMEL
During my Ph.D. I have studied how regularities and repetitions in language assist
people with and without dyslexia in learning and memory tasks. Ever since I
remember myself, I was curious about how we learn, remember, understand, and
process the information coming from the world around us. I am still very curious
about that, and lately also inspired by the way that my daughter studies the world. I
also like some things that are not directly related to science, such as chocolate balls
and Zumba. *eva.kelman@gmail.com
MERAV AHISSAR
I am a professor at the Hebrew University of Jerusalem. The research in my lab
focuses on auditory processing, learning, and memory in adults and children, and
special populations—people with dyslexia and people with autism. We use behavioral
experiments and measure neuronal activity using EEG and fMRI. The goal of our
studies is to understand these processes in depth and describe them computationally
for the regular population as well as for special populations.
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