DISCUSS basic model have been developed to
DISCUSS SOME OF THE WAYS IN WHICH RESEARCH IN ADULT AQUIRED DYSLEXICS HAS ENHANCED OUR UNDERSTANDING OF HOW PEOPLE READ.The use of language is one of the most complex tasks the human brain must carry out. The way in which children acquire language is studied very carefully. This acquisition is enhanced by teaching from skilled language users, but in itself acquired by the childs own observation and learning.
For this reason the acquisition of spoken language is perhaps more well documented then the taught acquisition of reading skills.It is hard to determine how the human brain deals with the task of reading the written word. It can not be determined by introspection or studying the human brain in action as this is not possible.
The way Psychologists and Neuroscientists have developed to determine hoe humans read is to observe people who have suffered some form of brain damage and have thereby incurred some form of reading disability. This disability is known as acquired dyslexia.From the study of such patients several variations of a basic model have been developed to highlight the way in which the written word is processed in the brain.
The model is subdivided in to two main processing routes, the Non Lexical Route and the Lexical route.A model produced based on theories from Coltheart (1981) shows that there are several routes to speech production in the brain. The eye first identifies the printed word. In the adult skilled reader the eye does not move in a smooth pattern but actually jumps to certain focus points in a sentence the brain itself actually fills in the missing words. It does this by top down processing in which the brain applies words to the sentence to make the overall meaning correct.
The eye does not move smoothly but actually jumps from point to point. The term given to the period when the eye is stationary and focused on a particular point is called a fixation. It is at these fixations when the eye takes up the information. The jumping movements are known as saccades.
Javal (1887) first used this term. This jumping in saccades allows information to be processed faster. However it is believed that little or no information is taken up during a saccade. This is known as saccadic suppression. Dodge (1900) and Holt (1903).In addition to this saccadic motion it has been discovered that in readers of English the perceptual span of the visual field is greater to the right of the fixation point. Conversely in readers of Hebrew it has been found that the perceptual span of the visual field is located to the left of the fixation point.
This indicates that the perceptual span in reading is learned as reading is learned and it is not preconditioned from birth. Rayner, Well and Pollotsek. (1980)Once the information is correctly converted to electrical impulses by the retina it is sent via the optical nerve to the brain. Many theories suggest that some of the component letters of a written word must be identified before the word is recognised. The early theory of letter identification was based on the fact that it was believed that templates were present in the brain to which the letters in written words could be compared. The main problem with this theory is that if letters do not appear to be the same we can still recognise them as the same letter. (e.
g. A and a.) An alternative theory to this has therefore been proposed.
This theory is based on the belief that humans contain a unit in the brain, which instead of containing letter templates contains sets of distinctive features which letters can be identified by. The written information is believed to enter the first processing unit of the reading model known as The Abstract Letter Identification unit. The information then has a choice of two routes from here. It can pass directly to the Letter Naming unit from which spoken letter names can be produced directly. On the other hand the information can pass to the Word Recognition unit (identified by McClelland and Rumelhart (1981) and Morron (1979)) or the Non Lexical Phonological unit.
If the information passes to the Word Recognition unit it can either pass to the Word Comprehension unit and then be produced as speech or it can pass to the Word Pronunciation unit and from there it is produced as speech. If the information passes to the Non Lexical Phonological Recoding unit it can be processed directly to speech or alternatively it can pass to the Word Comprehension unit and from there to speech. The direct route from sound to meaning is known as phonic mediation.
This model assumes that letter identification and word identification are independent. (See Flow Chart) An alternative theory is that letter identification and word identification would be accessed at the same time. McClelland and Rumelhart (1981). As humans hear sounds as they read silently it was assumed that meaning is accessed through sound.
An alternative theory is that in order for the meaning of what is read to be maintained in the brain then sound is needed. PRINT ABSTRACT LETTERLETTER IDENTIFICATIONNAMINGWORDNON LEXICALRECOGNITION PHONOLOGICALRECODINGWORDCOMPREHENSIONWORD PRONOUNCIATIONSPEECH SPEECHSPEECHSPOKEN LETTER NAMES The studies carried out to determine the routes taken within the brain as it processed the written word were undertaken by a variety of people over a wide timescale. Different research teams have identified several forms reading disability relating to specific parts of the brain.The ability and disability of brain damaged patients to identify types of written words has been recorded and from these results a corroborative model produced to explain the various forms of reading disabilities detected and from this the way in which humans read can be established.Beavois and Derousne (1979) identified a form of Dyslexia known as Phonological Dyslexia. With this particular disability sufferers are able to read and pronounce both complicated and simple words, however they are unable to read and pronounce even the simples of non words such as slimpo.
In the case of these Dyslexics the pathway between the Abstract Letter Identification unit and the Non Lexical Phonological Recoding unit has been damaged. The finding of such patients has substantiated the claim that these two units do exist in the brain and that a pathway connects the two of them. A study carried out on a patient named W.
B. who was diagnosed with acquired phonological dyslexia found that only 1 out of 30 non words could be pronounced. Funnell (1983)Marshall and Newcombe (1973) identifies a particular form of Dyslexia they termed Surface Dyslexia. In this case sufferers are able to pronounce regular words but are unable to pronounce irregular words. In this case the pathway connecting the Abstract Letter Identification unit and the Word Recognition unit is damaged.
This finding supports the model in seeming to confirm that these two units exist and that a pathway exists between them. The way in which patients with this form of dyslexia pronounce words is by phonic mediation which leads to the mispronunciation of irregular words.Lytton and Brust (1989) identified Direct Dyslexia. They carried out tests on a 70 year old man who had suffered a stroke which damaged the left side of his brain. The man was found to have poor speech comprehension and also had trouble naming objects. This indicated that damage had occurred to the pathway between the Word Recognition unit and the Word comprehension unit. This provided support that these two units exist and that a pathway between them also exists.
Several other forms of dyslexia have been discovered. Attentional Dyslexia affects the pathway between the Abstract Letter Identification unit and the Letter Naming unit. People who suffer from this are able to identify a single letter on its own using the Non Lexical Phonological Recoding unit but is unable to identify the letter when it is presented to them in association with other letters even if the letter is pointed out and underlined.Letter by Letter reading is another form of dyslexia. In this case sufferers are able to read words only by spelling them out in their head or aloud. This indicates that the only route to speech open to them is the letter naming route the other pathways have suffered some form of damage.
From the study of these patients and the construction of the word identification model it has been proposed that there are two routes to accessing word meaning and therefore reading. These routes have been termed the phonological route and the direct route. There has been a more recent suggestion of a third route to reading words aloud. A patient named W.T. could read aloud a wide variety of regular and irregular words.
However out of numerous non words presented to him he could only read 25% of the words aloud. It was thought therefore that there was some damage to the patients phonological route. In this case the patient should have been able to identify the words through the direct or semantic route. However when the patient was tested it was discovered that he had trouble understanding the words. In order to test the accessing of the meanings of the words W.
T was presented with low and high imaginability words. (i.e. Words which are easier to imagine or sound out loud.
) W.T. was then asked to pair certain words. e.g. W.
T. was presented with words such as refrigerator oven and stove. He was asked to pair the two word which were most alike. The patient had no trouble reading aloud but displayed trouble in trying to access meanings of low imaginability words.
Researchers then set about attempting to place this evidence in to the established model. It was concluded that there must be a direct link between the recognition units and the corresponding pronunciations. Coslett (1991)All of these patients have suffered some form of damage to the left hemisphere indicating that written words must be processed in the left hemisphere of the brain.
This indication has been further corroborated by an experiment which determined that words presented to the right visual field, which is connected directly to the left hemisphere, are processed much faster, in right handed people, than those presented to the left visual field. (Mishkin and Forgay 1950)It is clear that the experimental research carried on adult acquired dyslexics has led to the development of the model which has in turn identified two routes via which the human brain may access the meanings of words from the visual identification of the written word.The research on the patients has enhanced the understanding of how people read. However the understanding of how people read is by no means completely understood. Much research still needs to be carried out in order to determine exactly how this is achieved. Although the research on adult acquired dyslexics has led to the development of this model, and the identification of several routes via which information can be processed and understood this is based on humans who have been impaired in some way and the relevance to the unimpaired human reader needs to be examined in conjunction with this to further determine how a person reads.