The ability to put letters together and sound them out depends on the ability to represent the sounds in one’s own internal speech. This is why phonological coding is essentially concerned with how children can represent not only the sounds they hear, but also the sounds as they are associated with letters and words. We are not going to discuss in any detail the various aspects of how children perceive speech, how they do phonological coding, and, ultimately, how they produce spoken responses.
These three processes logically follow each other, that is, auditory discrimination of speech, transforming words into sounds, and then producing the speech sounds themselves. Let us simply say that if the child is not able to discriminate between different speech sounds, he/she will have difficulty in representing the sounds in the mind and this will lead to a defective production of spoken words and sentences. These three processes may be quite separate, that is, some children may not be able to perceive speech accurately but can read what is written without much difficulty.
Similarly, some children may be able to perceive speech distinctly but may fail to read words or sentences correctly. Finally, a child may be able to do both of these, but may have difficulty in representing them in their minds. The three activities occur in different places in the brain and the neural systems responsible for each activity could be quite distinct from each other. We have some evidence supporting this from studying the speech and reading difficulties of individuals who have suffered damage to different parts of their brains, resulting in very specific language problems.
Dictionaries in the head
We cannot teach children to recognize words only. We expect them to understand what they are reading. Thus, there is a dictionary in our heads for the sound of written letters/words (phonological coding lexicon) and for the meaning of the word (semantic lexicori). Some experts in the field of reading also think of a “pronunciation dictionary”. It is not enough that a child can recognize a printed word; he/she must also be able to pronounce it correctly.
The pronunciation of the word has to be assembled internally in the child’s mind. The next step is for the child to mobilize and organize the word’s speech production. Thus the child may have to carry three dictionaries in his head. The first has to do with print-to-sound translation, the second with pronunciation, and the third with the meaning of the word.
Sentences have syntax and meaning
Beyond single words, the child has to read sentences and this is when the third dictionary is often consulted. Also, the reader must have knowledge of the syntax of sentences. The syntax of a sentence and its meaning are like twins—one helps the other. A child can remember the meaning of a sentence by attending to its syntax. At the same time, a child can appreciate the syntax of a sentence better if he/she knows its meaning. What do we mean by appreciation of syntax?
Essentially, the reader is required to understand the se-quence in which the words occur in a grammatically correct sentence. Sequencing or successive processing, therefore, plays an important part in comprehension of syntax. On the other hand, the semantic aspect or the meaning of a sentence depends upon the way the child puts the ideas in a sentence together. The process of putting together all the ideas in the sentence and seeing their connection to each other requires simultaneous processing. These two processes are dealt with in the next chapter which discusses some of the difficulties encountered in reading development.
Brain activities are responses that accompany reading and speech
The neuropsychological picture of reading concerns the location of phonological coding as well as the oral output of a printed word. As far as we know from neuropsychological damage to the brain, there are distinct functional areas that are activated when, for example, an individual is reading a word, listening to a word, speaking a word, and generating a word. The area of the brain that is active when an individual is reading a word from print is in the occipital lobe, whereas the area that is strongly activated when a person is listening to a word is in the overlapping regions of the parietal and temporal lobes.
This does not mean that no other area is active when a person is reading a word from print or listening to a word. The brain activities seen in a Positron Emission Tomography (PET) scan overlap to some extent. However, the areas mentioned are maximally activated while reading a word from print as compared to listening to a spoken word. Similarly, when saying a word, the area that is predominately active is close to the front part of the brain.
Finally, the front part of the frontal lobe is the region of the brain that shows the most activity when a person is asked to generate words, such as when asked to say as many words as they can that end with the letter. These activities are recorded by PET and help us to understand the process of speech perception and speech production. Therefore, when there is a breakdown in the ability to read, we can analyze the difficulty in terms of these four different functions.
For example, when we wish to distinguish between different kinds of dyslexia or deficit in using words, we might ask whether the child has the same difficulty in listening to words and then reproducing them as he or she has in reading the word. It is possible that a child who has difficulty in reading the word can, nevertheless, listen to and reproduce the word without effort and vice versa.
If a child is unable to say the word or words, that is, cannot repeat spoken words, we must further examine the child to find out if the difficulty in speaking a word is related to words that he has listened to, or words that he has read, or to neither of these. Rather, the child’s difficulty may be detected in producing speech. Similarly, if the child has difficulty in generating words we must ask whether this difficulty is associated with or quite distinct from dyslexia.
We believe that there are many kinds of dyslexia, but neuro-psychological evidence now supports four distinct kinds of difficulties relating to words. It is, therefore, too simplistic to believe that poor readers have just one kind of deficit. As long as the neuropsychological processes associated with reading are poorly understood, our understanding of dyslexia must remain inadequate.