Presentation on theme: "PS2011 & PS2016 Cognitive Psychology – Dr John Beech The Acquired Dyslexias."— Presentation transcript:
PS2011 & PS2016 Cognitive Psychology – Dr John Beech The Acquired Dyslexias
2 The acquired dyslexias Introduction They are sometimes known as the “alexias”. The acquired dyslexias are usually acquired as a result of brain damage; but a couple of them can also be used to describe processes that have failed to develop. In a sense these are syndromes, ie they each have a collection of symptoms, but there is a great deal of variation so that individuals may not fit neatly within. What follows is just a brief overview of 4 of the acquired dyslexias: 1.Phonological dyslexia 2.Deep dyslexia 3.Surface dyslexia 4.Letter-by-letter dyslexia.
3 Phonological dyslexia: symptoms This condition was first described by Beauvois & Derouesne (1979) and occurs both in acquired dyslexia as well as in developmental dyslexia. We start here as it is a very common dyslexia as many children with reading problems appear to have some form of phonological dyslexia. The basic aspect is that there is a major problem with reading nonwords (e.g. glip, trank) compared to reading ordinary words and problems with unfamiliar words. A noteworthy aspect (to separate it from deep dyslexia—to follow) is that there is some degree of ability to read nonwords. Those with Phonological Dyslexia (PD) do not find it completely impossible. By contrast in deep dyslexia nonword reading is impossible. Reading of words in (PD) varies between % in tests. Some PD cases also show overlap with deep dyslexia, so there is some fuzziness.
4 Phonological dyslexia: symptoms Reading errors in PD are usually either derivational (e.g. woman – ‘women’; think – ‘thought’; leave – ‘left’) or visual (e.g. band – ‘bend’; panda – ‘ponds’). Obviously a better reader will commit fewer errors of this type. Some with PD have function word problems (e.g. an – ‘and’; is – ‘his’). Others apparently have no such problems. But even these may have great problems reading function words in text even though they can read them in isolation. Theoretical interpretation There appears to be damage to the non-lexical (phonological) route: AbstractLetter-to-Phonological letter soundoutput Identification rulesbuffer
5 Phonological dyslexia: causes There could be damage to any part of this route. But although such damage means that reading nonwords is very difficult, there should be no problem with real words. This is because they can be read by means of a lexical route (ie. reading by accessing word units), as in the dual-route theory of reading. Coltheart (1985) proposed that the precise location of such damage in PD determines the type of PD. For instance, some have problems with strings of letters and converting these into graphemes (e.g. SH-O-CK – 3 graphemes out of 5 letters). Children with PD invariably have problems with phonics.
6 Deep dyslexia - symptoms All patients with deep dyslexia (DD) have had considerable damage to their left hemisphere. This produces aphasia* and hemiparesis*. Patients have a considerable number of problems, esp. in reading: Semantic errors (weigh – “anchor”; brown – “black”). Nonwords (e.g. blard) are not read or mistaken for a real word (“lard”)– called lexicalization. Function words (e.g. the, or, also). Visual errors (e.g. band – ‘bend’; panda – ‘ponds’). Concreteness: Concrete nouns (e.g. table, phone) are read better than adjectives, verbs and abstract nouns (e.g. humour). Morphological errors where the root of the word is correct, but the affix is wrong (e.g. blender – “blend”; unkind – “kind” Writing may be impossible because of the hemiparesis. *Aphasia = loss of language production *hemiparesis= partial paralysis to one side of the body
7 Deep dyslexia: its cause Coltheart (1980) has proposed that DD is unique because it is not using a damaged reading system, instead the whole of the left hemisphere is out of commission. This means that only the right hemisphere is used for reading. Patterson et al. (1987) in support of this reports a case whereby because of abnormalities, a 15-year-old had her left hemisphere removed. Before she was a normal reader, but after she had all the major symptoms of DD.
8 Surface dyslexia: symptoms The major characteristic is sensitivity to spelling regularity. Thus there are no problems with regularly spelled words (e.g. hint), but considerable problems reading irregularly spelled ones (e.g. pint, choir, island). When making these errors those with surface dyslexia (SD) consider that what they say is the actual word. E.g. shoe will be read as “shO” (as in show) and the reader will think the word is actually show. The length of words affects the reading time in SD. Nonwords – do not pose any problems. There are none of the symptoms of phonological or deep dyslexia.
9 Surface dyslexia: interpretation SD suggests reading by applying letter-sound rules. So irregular words (also known as exception words) produce regularization errors (e.g. choir – “choy-er”). This in turn suggests damage to a lexical route—a route involving processing word units. The figure shows KT (McCarthy & Warrington, 1986) who has pure SD although some exception words are read accurately, performance is a lot worse than for regular words.
10 Surface dyslexia: interpretation KT suffered from semantic dementia due to deteriorating temporal lobes. Thus semantic knowledge was deteriorating. This probably accounts for deterioration in processing word units, but a relatively intact letter-sound translation system. An alternative interpretation for SD, probably less plausible, is that word analogies are being used inappropriately (e.g. Patterson, 1981). For instance, broad is pronounced as “brode”, because of the embedded word road. Developmental surface dyslexia is also in evidence (Castles & Coltheart, 1984). These are children who have grasped phonics relatively easily, but find it difficult to develop their sight vocabulary. They too make regularisations when encountering irregular words.
11 Letter-by-letter reading: symptoms Otherwise known as pure alexia. As implied by the name, words and nonwords are read letter by letter. In practice this means that they are spelled out aloud (e.g. “n-u-t-m-e-g… nutmeg”). (The spelling part is aloud, whispered, mouthed or silent.) As might expected this means very slow reading times that increase as a function of word length as shown on the right. Single letter reading is usually OK, but some patients make errors (rind – “r-i-n-g…ring”).
12 Letter-by-letter reading: symptoms There are no problems in writing. But because of the condition after a patient has written something they can’t read it, which is very frustrating. Cursive handwriting is particularly difficult for them as the individual letters are not separated. Understanding of language and producing language is normal. Areas of damage Lesions are in two sites…
13 Letter-by-letter reading: symptoms Areas of damage Lesions are in two sites: 1.Left occipital region – this results in right hemianopia*. This effectively disables normal reading ahead. Psychologists can present words to the left visual field. 2.The splenium - posterior of the corpus collosum. Both these lesions are usually present. In normal functioning (ie. NOT in L-by-L) words to the right visual field are processed by the left visual cortex and then the splenium transfers information between the hemispheres. But obviously in L-by-L this can’t happen. The result is the slow letter-by-letter reading. *Hemianopia = inability to see a visual field, in this case to the right of fixation.
14 Letter-by-letter reading: unconscious reading There is anecdotal evidence that soon after initiating the spelling out of the words L-by-L patients actually know what it is. To test this Shallice & Saffran (1986) presented words and nonwords briefly (1-2 sec durations) and asked them to guess if it was a word or nonword. Reluctant to do initially, but they score well above chance indicating that semantic information is available.
15 Summary of 4 acquired dyslexias Types of dyslexia PhonoDeepSurfaceL-by-L 1. Word v. nonword 2. Spelling regularity 3. Word length 4. Concreteness? 5. Content v. function? 6. Semantic errors?