Dyslexia is a disorder which affects a person’s ability to read fluently, despite normal intelligence and comprehension. In order for a person to read, they must be able to decode the words and understand them – both of these processes are needed.
It can also affect a person’s writing – letters are likely to be written backwards and words can be spelt wrongly. Words are often written as they sound, and individuals have a poor phonological awareness. It is thought that English speakers show more severe effects of dyslexia due to the difficulty of the language- it had several irregular verbs and spellings, and therefore takes longer to learn than other European languages such as Italian.
Here are examples of the word ‘teapot’ written by different individuals with dyslexia.
There is a genetic basis for dyslexia: males are more likely to be dyslexic than females. The genes associated with this disorder have been identified on chromosomes 6,15 and 18. Neuroimaging studies have shown that there are also differences in the brain between dyslexics and normal controls: areas connecting language and visual areas show less activity in dyslexics. There is also evidence that there are structural abnormalities in Broca’s and Wernicke’s areas (shown in the diagram below).
Individuals with dyslexia can be helped to improve either reading and writing skills by using techniques which increase their awareness of the relationship between letters and sounds. Certain fonts (see picture below) are thought to help dyslexics read more smoothly, as they emphasis the difference between letters. Different coloured backgrounds are also used. It is thought that extra help when the brain is still developing makes training more effective.
That’s all for now – make sure to request any topics you’d like me to write about 🙂
I’m going to talk about language in my next few posts, so here’s an overview of the language areas in our brain. As you will see, there’s a lot that goes on in a very short space of time for us to be able to understand speech and reply appropriately, but I’ll try and make it as simple as possible.
Here is a diagram of the brain showing the main areas involved in language processing. As you can see from the diagram, it is the left hemisphere which is specialised for language (the frontal lobe is on the left):
The auditory cortex is the part of the brain that processes speech, and enables us to make sense of it. The motor area then controls the vocal tract, throat, tongue and mouth so we can talk. Broca’s area, shown in purple on the diagram, is the inferior frontal gyrus, which is important for language production. Broca (1861) studied a patient who was unable to produce speech other than the word ‘tan’ and swear words, but could understand questions. This patient had a huge lesion in his inferior frontal cortex, so Broca concluded that this area is important for speech. He studied several patients with lesions in this area, and found that only those who had lesions in the left hemisphere had impaired speech, which shows that the left hemisphere is important for language. Patients with Broca’s Aphasia are able to produce single words but not full sentences.
Wernicke’s area is the posterior part of the superior temporal gyrus, and is important for speech understanding. Wernicke (1874) was the first to describe patients who had lost the ability to comprehend speech despite normal hearing, and could not produce meaningful speech despite normal articulation and grammar. Patients with Wernicke’s Aphasia have fluent speech but it is lacking any content or meaning.
This next diagram shows how Broca’s and Wernicke’s areas are thought to interact to produce speech, based on the Wernicke-Lichtheim Model:
The arcute fasiculus is the white matter that connects the two areas. If it is cut, then Conduction Aphasia occurs – this is when speech sounds and movements are unaffected, as well as normal comprehension, but repetition of speech is impaired.
Check back soon for my next post on how infants develop language abilities!