Theories on the Causes/Effects of Dyslexia
On the third day of the Learning and the Brain: Neuroscience of Reading summer institute, Dr. Gabrieli shared some other theories about presenting causes/effects (it’s very difficult to determine which is a cause and which is an effect) of dyslexia. One of these was that of rapid auditory processing. In the English language, many of the letters, and in fact, even entire words are nearly identical in the sound waveforms that they produce. For example, the waveforms for the words “stay” and “say” are identical, other than a 100 millisecond silent gap in “stay”. We are so attuned to miniscule variations that we can identify such a difference and use it to inform our comprehension. Gabrieli referenced a study that showed that non-dyslexic readers were able to distinguish rapid sounds much better than readers with dyslexia. Those with dyslexia increased their accuracy significantly when there was more of a gap between the delivery of each sound stimulus. There is a strong correlation between reading ability and ability to pick up these incredibly subtle differences in sound.
Gabrieli also spoke of the anchoring hypothesis. This was a study that showed that non-dyslexic readers were able to identify and use tonal anchors in speech essentially as a landmark from which they could reference other sounds. When the same test was given to readers with dyslexia, they were unable to use the anchor tones in this way. Gabrieli suggested that it could be that this is an issue related to learning rather than perception. The control students were not told to use the anchor tone. In fact, they were not even told that there was an anchor tone. Regardless, they were able to learn a cue and use it essentially as their own scaffolding and then further build their learning from there. Children with dyslexia, however, were unsuccessful in identifying or using the anchor tone to guide their learning.
Another interesting study was conducted to investigate magnocellular processing. A study on this found a 27% reduction of size of magnocellular cell bodies in the lateral geniculate nucleus of those with dyslexia (Livingstone and Galaburda, 1991). This is significant because this is the part of the brain that is sensitive to visual motion. When people with dyslexia are shown a series of moving dots, they had an abnormal brain response. This is surprising, since reading doesn’t involve motion, but perhaps it is connected to the fact that our eyes are constantly moving as we read and to the fact that many dyslexic readers have difficulties with visual tracking. Research suggests that practicing reading makes a very significant impact on the development of the motion area of the brain.
There was also evidence presented from multiple studies that suggests that those with dyslexia have much more difficulty identifying anomalies in visual cues than those without dyslexia. Again, this is not surprising since one would expect strong readers to be able to pick up to slight visual cues, just as they would pick up slight auditory cues.
Reading Interventions for Students with Dyslexia
Gabrieli began this lecture with an apology. The fact of the matter is that neuroscience does not have much to offer in terms of data here. There is very little data from neuroscience regarding the ‘how’ of intervention. He stated that the question of ‘now what’ – what can we do to better serve students than we did before – really remains to be answered. This is due to many reasons, one being the logistics of conducting a major study requiring students to receive fMRIs, given that MRI machines are not at all portable. Another reason for the difficulty in studies in this area is that one of two options has to be pursued: 1) a control group is deprived of the interventions given the test group. This seems rather unethical – to take struggling readers and intentionally deprive them of the supports that they need. 2) Give the intervention to the control group slightly after it has been given to the test group. This allows the initial research to be done while not depriving either group of the intervention that they need. The problem with this, however, is that there no longer is a control group to be used in longitudinal studies.
It is necessary, when examining reading intervention programs, to note the difference between programs that are based on research, and programs that have themselves been researched. The former is fairly common but the latter is incredibly rare.
The research has consistently and clearly demonstrated the plasticity of our brains. Adult brains exhibit no less plasticity than children – both are capable of incredible growth, change, and development. As was stated in an earlier post (The Neuroscience of Reading – Part 1), I am grateful that the data shows such a propensity towards brain growth and development because it marries so well with the work that Carol Dweck is doing on growth mindset.
The simple summary here is that neuroscience does not tell us what interventions to use, but it does indicate a couple of things:
- It very strongly supports the practice of using interventions in general.
- It supports the use of interventions as early as possible. The earlier the intervention, the better it seems to work. By grades three-four range, the type of interventions that work well for the younger students really don’t have the same effect anymore.
- It also indicates, as Gabrieli stated, that there is a pretty big diversity of students who need a pretty big diversity of help. A one-size-fits all approach to reading intervention is not going to work and the neuroscientific data certainly agrees with that.
One consideration that I’d like to share is something that came up over and over through the duration of this course. It is that of the importance of practicing reading. The research that was presented to us showed that regular reading helps develop multiple areas of the brain. It was really clear from the research that the benefits of reading on brain growth and development cannot be overstated. Unfortunately, for those with reading disabilities, they tend to get stuck in a cycle: reading is difficult so they do less of it, but not reading does not help make it be any easier. The less reading they do, the more the ability gap widens between them and their non-dyslexic peers. Likewise, for those who enjoy reading, the more they enjoy it the more they read; and the more they read, the more they develop their reading skills. Thus, the reading ability gap continues to widen in each direction. Gabrieli shared that in grade five, a good reader may read as many words in two days as a poor reader does in a year. Again, this speaks to the importance of early intervention. If we can intervene early so that readers with dyslexia can learn how to compensate early, we might be able to reduce that ability gap at least somewhat.
Also in light of the increased effectiveness of early intervention, it seems prudent to consider how we might be able to be proactive rather than reactive in our approach to reading interventions. Typically it is only after a child fails to develop reading skills that we intervene. What could we do to intervene before they fail? In the future, this might be an area where neuroscience could play a role. In the meantime, the best predictors of future reading difficulty in prereaders are deficits in phonological awareness, rapid naming, and letter knowledge. Additionally, there are multiple predictive indicators that relate to a child’s ability to rhyme.
Another role that neuroscience can play is to simply show the differences in brain function of a typical reader and a reader with dyslexia. To see the very visible differences in brain function can be very empowering to a struggling reader and their family. To know that the deficits are not due to a lack of intelligence, a lack of effort, or any other such factor, but rather due to a very legit brain difference – that is powerful knowledge.