Assesment of Reading Difficulties in Patient AM Following the Development of Vascular Dementia.
Assesment of Reading Difficulties in Patient AM Following the Development of Vascular Dementia.
ABSTRACT
INTRODUCTION
Dementia was defined by Cummings et al. (1980) as 'an acquired, persistent impairment of intellectual function with compromise and at least of the following spheres of activity: language, memory, visuospatial skills, emotion or personality and cognition.' Dementia occurs as a series of subtypes, one of which is known as vascular dementia (Brown, 1993).
Vascular dementia is a disease which is most commonly caused by impairment to the circulatory system of the brain following damage caused by a stroke (Alzheimer, Scotland., 2002). Vascular dementia is found to be most prevalent in people aged 60-75 years and is more prevalent amongst the male population in comparison to female.
Vascular dementia is seen to result in progressive deterioration of the higher functions of the brain for example memory, recognition, the ability to learn new information and fine motor movements (Alzheimer, Scotland, 2002). These changes commonly occur in a stepwise pattern due to the sudden occurrence of strokes.
The features common to vascular dementia which characterise the disease include loss of memory and problems with forgetting recent events. The clarity of speech may alter resulting in difficulties in communicating. Patients may become poor at expressing themselves with problems thinking of the words appropriate to what they want to say as well as understanding the words of others, resulting in slow and effortful speech. Both reading and writing abilities may also be affected in similar ways to speech, all disabilities which can be very frustrating as well as debilitating for the patient. Further cognitive problems may occur in the ability to plan as well as solve problems which patients are often very slow at doing, or else unable to perform such cognitive actions. Problems may also be more physical, with difficulties walking due to weakness of limbs and often occur in loss of awareness on one side of the body. Disorientation frequently occurs in both time and place (Tadd, 2002). These problems which may be experienced by the patient following the development of vascular dementia result in major changes to the patient's everyday lives, which may often result in a loss of independence which can be frustrating for both the patient and their families.
This project looks at the case of patient AM, which will be discussed in greater detail further in the report. AM has suffered vascular dementia resulting in severe reading difficulties among other things. It is however these reading difficulties which have been addressed in this investigation and will be discussed in detail throughout this report.
Reading disorders which occur due to brain injury are known as acquired dyslexias. A distinction between two main types of dyslexias was made by Shallice and Warrington (1980) these two main types being central and peripheral dyslexias. Peripheral dyslexias were classified as affecting the early stages of visual analysis of letters and words whilst central dyslexias account for those subtypes in which deeper processes such as graphene-phonene conversion or semantic access are affected (Ellis and Young, 2000). A model of reading was proposed by Ellis and Young (2000) and this model can be used to demonstrate the stages involved in reading allowing clear demonstration of those stages which are impaired resulting in different types of dyslexia. The model which can be seen in appendix A (Ellis and Young, p 192) is useful in illustrating and aiding explanation for problems associated with specific dyslexias and the areas of damage which lead to the development of such dyslexic problems.
Those dyslexia types which occur as subtypes of the central dyslexia classification include; surface dyslexia, phonological dyslexia, semantic access dyslexia and deep dyslexia. In contrast it is the peripheral dyslexias with which I am concerned in this report. The peripheral dyslexias being; neglect dyslexia in which a words ending is often preserved with its beginning altered. Letter by letter reading is a disorder in which words can only be identified and successfully read after having named each letter individually either aloud or sub-vocally. Visual dyslexia is a type of dyslexia in which words are misidentified as other words. Finally attentional dyslexia which occurs when perceptual grouping is disrupted due to brain injury which prevents the visual analysis system from grouping letters together which form a specific word and exist in a particular position on a page, thus producing difficulties in being able to read and follow text (Ellis and Young, 2000).
The first case of attentional dyslexia was reported by Shallice and Warrington (1977). It was found that in two patients the visual presentation of more than one stimulus item belonging to the same category presented simultaneously impairs the ability to identify the item. The two patients were further researched using a variety of experiments in order to investigate their apparent inability to identify objects in simultaneous visual presentations. It was demonstrated using experiments in which letters were flanked by letters that patients were able to name letters individually but picking one letter from a string of letters proved somewhat more difficult.
Another patient, BAL, was reported by Warrington et al. (1993) and BAL's performance was similarly tested using flanking tasks. BAL was able to name letters accurately when presented individually yet when flanked by items of a similar category the ability to name the target was significantly impaired. This pattern of impairment for single letters was also demonstrated with words. BAL was unable to read even a simple written passage with such severity that he was unable to read even a short string of words, even just two words following each other. From the study of patient BAL, Warrington et al. (1993) concluded that BAL was an attentional dyslexic and that attentional dyslexia was caused by "a disorder of a controlled system governing a parallel - to - sequential translation in the reading process" (Warrington et al., 1993, P.882).
More recently Saffran and Coslett (1996) present the case of patient NY who demonstrated a marked difference between his ability to read single words presented individually which was preserved in comparison to his ability to read text. Despite his accurate ability to read single words, which was demonstrated by his good performance on a test known as the AM-NART, NY had given up any attempt to try and read text. NY was reported to complain of visual problems as contributing to his major problem with reading, reporting stopping trying to read text altogether due to the appearance of the words "running together." Research into the case of NY showed he was able to read 96% of 200 single words consisting of 4-5 letters correctly, abnormalities did however begin to show on introduction of a second word. A frequently occurring problem reported with attentional dyslexia is the production of errors which reflect the migration of letters from surrounding words into the target. Migration errors have also been reported in the case of patient FL (Mayall and Humphreys, 2002). FL is however able to read passages of text and it is suggested he is able to use physical cues in order to focus attention on the individual words in the text allowing him to read. Thus the case of FL provides further suggestion of possible ways in which attention is used in reading. For example Mayall and Humphreys (2002) suggest following evidence from FL that the possible processes involved in directing attention between separate words on a page exist independently of those involved in focusing attention within a single word. It is suggested that FL maintains an intact representation of separate words as well as an intact ability to switch his attention between one word and another in text. His impairment may lie in focusing his attention within each word which results in competition for a target identification response from surrounding letters (Mayall and Humphreys, 2002).
Various explanations for attentional dyslexia have been proposed following examination of the research obtained from the cases of attentional dyslexic patients (Shallice and Warrington, 1977, Warrington et al., 1993, Saffran and Coslett, 1996, Davis and Coltheart, 2002 and Mayer and Murray, 2002). It was proposed by Shallice and Warrington (1977) that the deficit resulting in attentional dyslexia exists between the stages of perceptual classification and semantic processing. (refers to the visual input lexicon and semantic system in the reading model appendix A). It was proposed that problems occur when attention must be distributed between two items. Shallice and Warrington (1977) suggested that the knowledge about the rough position of letters within a word, which is necessary in order to form familiar and distinctive letter combinations which can be identified as words get mixed up resulting in words becoming confused and being unable to identify the words to read them.
It was later reported by Warrington et al. (1993) that Shallice had made a claim that attentional dyslexia was a result of damage to a control mechanism. It was proposed that an attenuating filter exists which reduces the output of letter level analysis outside the appropriate window in the visual field. Impairment to this filter allows output from parallel levels of stimuli analysis to occur in parts of the visual field other than the target word thus allowing activation of units at the word form level for words other than the target. Letters forming the target word would normally be selected for processing and have access to the word form system. However failure to attenuate and exclude non-target items leads to faulty processing at the word form level. Shallice concluded that a second filter exists which controls the transmission from an orderly parallel mode of operation at the level of visual word form to a serial mode for access to semantic and phonological representations.
NY (Saffran and Coslett, 1996) was given naming and auditory word - picture matching tasks which showed NY had little problem in recognizing visually presented objects generally. His capacity to use selective attention during a visual search is clearly limited. It is suggested that his poor performance on flanking experiments could be due to an inability to set his attentional window to exclude the flanking letters. It is further suggested in the case of NY that he experiences a loss of location information which is a significant factor leading to his reading impairment, the migration errors which can be seen in NY reflect a failure to link objects to locations in external space it is thus possible that NY has sustained damage to the mechanism responsible for mapping spatial locations, this would account further for his attentional dyslexia.
A distinction between BAL and NY was that BAL's deficit appeared to be specific to verbal materials. Attentional dyslexia is described in the cases of BAL and NY as "susceptibility to interference from surrounding words which can be manifest at different stages in the processing of graphemic information. It is the factors underlying this susceptibility which may differ across patients" (Saffran and Coslett, 1996, p.226).
Davis and Coltheart (2002) proposed a similar explanation for attentional dyslexia to that of Shallice. They proposed that when there are multiple items to transmit an attentional control mechanism is required to select and attend to one item at a time. If this mechanism is damaged attentional dyslexia will result.
Attentional dyslexics have difficulty focusing the attentional window appropriately due to brain damage. A wide attentional window can result in a loss of location information allowing letters to drift between words. This would account for the migration effect seen in the cases of both NY and FL. ...
This is a preview of the whole essay
Davis and Coltheart (2002) proposed a similar explanation for attentional dyslexia to that of Shallice. They proposed that when there are multiple items to transmit an attentional control mechanism is required to select and attend to one item at a time. If this mechanism is damaged attentional dyslexia will result.
Attentional dyslexics have difficulty focusing the attentional window appropriately due to brain damage. A wide attentional window can result in a loss of location information allowing letters to drift between words. This would account for the migration effect seen in the cases of both NY and FL.
Finally Mayer and Murray (2002) report patient WS and propose and explanation to account for the differences in attentional effects which can be seen between patients. They propose that when damage occurs to the brains attentional system, 'selective engagement' which is involved in the attentional processing of lexical - semantic information is impaired. Damage to selective engagement as well as a vulnerable visual attentional system are suggested to account for the differences noted between WS's ability to decode simple texts in comparison to more complex text which requires focused attention and inferential abilities (Mayer and Murray, 2002).
What is less clear is if the problem of attentional dyslexia is a problem which is specific to reading and if it is at what stage of the reading process it occurs (Warrington et al., 1993). BAL maintains the ability to name pictures from arrays indicating his attentional deficit arises after a stage of visual processing in which undifferentiated visual features are selected for further processing, therefore for BAL his attentional deficit is specific to reading. In contrast Shallice and Warrington (1977) suggest the pattern of performance in their patients are nit restricted to verbal stimuli but include other th9ings such as shapes. It has been argued that deficits such as these result from a general impairment rather than damage to a specific reading ability (Behrman et al., 1998). Evidence can be seen as presented by Behrman et al. (1998) which suggest problems in terms of alexics occur due to a more fundamental perceptual problem and argue that because reading is a relatively new cognitive ability it is likely to be mediated by a neural substrate which subserves other visuoperceptual functions and this system is used at a general level to mediate the processing of the alphanumeric symbols required for reading (Behrman et al., 1998).
This study looks at patient AM and the nature of his reading difficulties. The tests carried out suggest AM is suffering from attentional dyslexia to some extent. The evidence from this proposal will now be discussed and the nature of the disability as specific to reading or existing as a more general problem and thus indicating the existence of a general area of the brain which encompasses the ability to read will be considered.
CASE DESCRIPTION
Patient AM is a right-handed 62 year old male. AM initially suffered two mini-strokes (TIA's) followed by the occurrence of a major stroke on the 13th February 2002, a second major stroke occurred 7 months later in September 2002. On recovery from these strokes he was noted to present symptoms of vascular dementia and was later diagnosed as having the disease. The disease resulted from AM having suffered a left occipital infarct leaving him with a right homonymous hemianopia.
Before suffering from his initial major stroke AM worked as a transport manager. He had been a keen reader but has since been unable to read more than a line or two of text of which he finds it difficult to follow the content and give it meaning reporting "everything is mixed up. The more I concentrate on it the worse it becomes." A series of initial tests were carried out in order to determine what sort of problem AM was suffering from thus allowing a more thorough examination of his symptoms to be carried out.
Initial testing showed AM to have a digit span of three which is low for a man of his age. Tests were also carried out using the VOSP. Results obtained from testing using the VOSP demonstrated that AM maintained a normal ability to perceive objects with exception of the incomplete letters task on which he scored 12 / 20 a score that is below normal for an average person of the same age. His ability on the tasks from the VOSP designed to assess space perception varied. He performed at a normal level passing both the dot counting and cube analysis tests but failing the position discrimination task with a score of 12/20 and the number location task on which he scored just 6/20.
Poor performance on both the position discrimination and number location tasks suggested AM was experiencing problems in the area of attention and thus further tests were carried out to investigate the extent and nature of these attentional problems.
AM was given three tests from the test of everyday attention in order to investigate his attentional problems. Firstly AM completed the map search on which he obtained a score of 61.8. On comparison of this score with that of the average for someone of AM's age AM's score was shown to be more than 2 standard deviations away from the normal average and lying in the first percentile for his age group, thus meaning out of 100 people only one will score as poorly as he did providing a strong indication that this result is abnormal.
AM simililarly showed poor abnormal performance on the telephone search task. On comparing his score with that of the mean for people his age AM's score is shown to be 4-5 times slower than the slowest control score. AM's score lies below the first percentile which indicates a highly abnormal performance as out of 100 people noone is likely to score as poorly as AM. Finally AM was given the lottery test from the test of everyday attention. On this test requiring auditory attention as opposed to visual required in the previous two tasks, AM performs at a level consistent to that of the 25th percentile for his age group and thus this score is not in any way abnormal.
Following analysis of the results of these tests I went on to investigate this attentional deficit further with a focus on it's relationship to AM's reported reading problems. Several tests were developed and used alongside more standard methods of testing in order to carry out this analysis. The methods for these tests as well as the results obtained will now be presented and discussed.
SET OF EXPERIMENTS 1
The first set of experiments carried out looked at AM's ability to read single letters.
METHOD
AM was given a series of tests, taken from the PALPA battery of tests. Firstly AM was given a letter naming task in order to determine his ability to read single letters presented alone. The letter naming task required AM to simply name the letters of the alphabet which were presented individually in their upper case form.
He was then given an upper and lower case matching task which was followed by a lower to upper case matching task. Both tasks involved matching the correct upper case letter to its lower case equivalent from a choice of two letters, the second letter being a distracter which was visually similar to the target and vice versa according to which test was being done. Following this AM was issued the mirror reversal test in which he was required to distinguish between the correct form and mirror reversed forms of individual letters. The final test which was given looking at individually presented letters was a letter by letter flanking task. The test consisted of 25 trials of letter strings with 5 letters presented in each string, 2 letters located either side of (or flanking) the target and each letter different. The letters were presented in size 12 print with Times New Roman Font and only a single space between each letter. ( A copy of the test can be seen in appendix B1). AM was required to pick out the letter which was underlined in each letter string and represented the target.
RESULTS
On the letter naming and sounding tasks AM scored 24/26. This score is below normal for average controls who would score 26/26. AM's errors were however repetition of letters which were listed either immediately prior to or after the target letter. On the lower to upper case matching task AM scored 26/26 and scored 25/26 on the upper to lower case matching. Scores on both these tests were seen to be normal with average control scoring 26/26 and 25.96/26 on the 2 tests respectively. Furthermore on the mirror reversal task AM scored the top score of 36/36 which is again equal to that of the score of an average control. AM's performance on the letter by letter flanking task was also faultless, scoring a maximum 25/25.
DISCUSSION
The results of these tests which look at ability to read single letters highlight that AM is not impaired at this level of reading. He is able to read single letters accurately and recognizes them in both the capital letter and lower case form. The results of the letter naming and sounding task on which AM scored 24/26 below average for a normal control who would score 26/26. These results taken at face value suggest AM is impaired in his ability to read single words. However on analysis on the 2 errors made in this task it is clear that AM does not lack the ability to name these letters but that letters listed before or after the target letter have been repeated. This is due to an attention problem in tracking his place on the page rather than an inability to read single letters correctly. Ultimately the results of these tests highlight that no impairment lies in the ability to read single letters with a mild attentional deficit occurring at this level in tracking the position on this page.
SET OF EXPERIMENTS 2
The second set of experiments carried out looked at AM's ability to read words of various lengths when presented individually.
METHOD
AM was again given a series of tests taken from the PALPA battery in order to investigate his ability to read single words. These tests were presented alongside some other specific tests designed to look at various aspects of his word reading ability and attentional problems.
AM was firstly given a test of non-word repetition which examined his ability to repeat unfamiliar but word-like sound forms. He was next given a spoken word-picture matching task in order to assess his semantic comprehension ability. The task required AM to match a word which was said aloud to him to one of 5 pictures presented on the page. One of the 5 pictures being the target which corresponded to the target word whilst the other 4 being distracters in which one was a close semantic distracter from the same subordinate category as the target, secondly a more distant semantic distracter, as well as a visually similar distracter and an unrelated distracter. Next a written word-picture matching task was given. This task being the same as the previous task except the words to be matched to the pictures were presented in written form thus requiring AM to read and understand the words. The next task taken from the PALPA was the visual lexicon decision with illegal non-words task. This task was presented as a series of written non-words which were made up of letter pairings which do not occur in written English and were very difficult to pronounce. AM was required to read these words aloud. A letter discrimination task was then given in order to examine AM's ability to match upper and lower case letters in multi-letter strings. Letter strings containing 5 letters were presented in written form, pairs of words and non-words were presented in which in half the cases the letter strings were identical in upper and lower case form, in the other half different letters were presented in either the upper or lower case string which varied by only 1 letter. AM was required to identify which pairs of words were the same and which were different.
A series of PALPA tests looking at various aspects of image ability and frequency were next used. Firstly image ability and frequency repetition. A list of words varying in image ability and frequency were read aloud and AM was required to repeat what he heard after each word. This was followed by an image ability and frequency reading task. AM was presented a list of words, half high image ability and half low and half the words in each of these groups high in frequency and half low. AM was required to read these words aloud.
In a non-word reading task AM was presented a list of non-words which again had to be read aloud. Image ability and frequency spelling was the next test given. The first in a series of tests looking at spelling. The test required AM to write a word down following hearing it. The list of words presented varied in image ability and frequency. The next task known as regularity and spelling looks at whether spelling to dictation is affected by sound-spelling regularity. AM was required to spell when writing down a word which was presented orally from a list of regular and exception words which were matched for word frequency, image ability, grammatical class and number of letters and syllables. The next 2 tests looked at AM's reading and spelling ability when the letter length of a word was varied. AM was presented with a list of words which he had to read aloud or was presented the list orally which he was required to spell in the spelling condition. The words presented varied from 3 letter strings to 6. In the letter length reading condition AM was timed on how long it took for him to read each individual word.
The final test taken from the PALPA looked at picture naming, oral reading, repetition and written spelling. A list of words was presented to AM in various forms for example in written form for the reading task but presented orally for the repetition and spelling tasks and pictures representing each word were presented in the picture naming task. AM was required to name, read, repeat or spell the words which were the same for each condition. In all cases of the PALPA tests his answers were recorded and scored in order to derive the results for these tests which will be discussed shortly.
The remaining tests which AM was given to look at single word reading were developed specifically to investigate his ability to read single words focusing on his attentional abilities.
A word by word flanking test was issued which was carried out in the same way and presented in the same way as the letter by letter flanking task discussed previously. The words in the flanking task were 3 and 4 letter words and each word in a trial was unrelated and of the same length to those flanking it. No words in one trial were the same. All words were presented in capital letters in size 12 print, Times New Roman Font and with single spacing between each word. (See appendix B2 for an example of the test given).
AM was also given a test in which every word from a short text were taken and presented individually in a list form which maintained the original order in which the words had appeared in the text. AM was later presented the words in individual sentence form as well as in paragraphs. These tests will be presented later. (an example of these tests can be seen in appendix B4).
One hundred and ninety words were presented in the first trial and AM was required to read the words aloud. The time taken for him to read all 192 words was measured. A second trial used the same method but using a different text consisting of 158 words. AM was required to read this word list and was timed in the same way as in the first trial but he was only presented the single words after having read both the paragraphs and sentences. Both trials were also given to 6 controls of similar age to AM in order to determine the time it takes for a normal person to read such text in its different forms allowing comparison of AM's performance from that expected on average from a control of similar age who lacks any neurological problems.
The final test used to look at AM's single word reading was a computer based test designed to look at the speed with which AM was able read single words which varied in letter length, frequency and image ability. Words were presented in a random order in terms of length, frequency and image ability on a Toshiba lap top computer. Words appeared in the centre of the computer screen in black, size (?) (font) print on a white background. Before each trial, of which there were 91, the word "ready?" was presented in the centre of the screen. When ready AM was required to press any button on the keyboard which triggered the word "ready?" to disappear and be replaced by the target word after an interval of (?) seconds. The target word remained on screen until AM responded to it by saying it aloud into a microphone which was attached to a headset worn by AM. When the microphone was triggered by AM uttering the word it disappeared from the screen and was replaced by the word "ready?". This process was repeated for 91 trials. The reaction time taken from the moment the target word appeared on the screen and was spoken into the microphone was recorded and measured in milliseconds by the computer.
RESULTS
The results obtained on the PALPA battery tests are scores all representing a normal level of performance which compared when compared to the average score of a control. AM's scores on the PALPA battery tests along with the mean score for a control are presented in table 1.
INSERT TABLE 1
On the word flanked by words task AM scored a maximum 25/25. He was also able to read each of the single words taken from the text correctly when presented individually in both trials. However the time taken to read these word lists were 8 minutes and 45 seconds for the first trial and 5 minutes and 26 seconds for the second. On comparison of these times with that of the average time taken for an age matched control to read the word lists (?), AM's performance can be seen to be significantly slower than the controls by (?) times.
The results for the computer based assessment were recorded as reaction times in milliseconds by the computer (see appendix C). Analysis of these reaction times was carried out using a univariate ANOVA in order to determine any significant interactions between reaction times and word image ability, frequency and length. Analysis of the results produced by the ANOVA show there is no significant effect of frequency F= .167, P= .684 or image ability F= 2.17, P= .145 but a significant length effect F= 6.74, P= .002 on AM's reading ability. No significant interactions were seen between length and frequency, F= 1.93, P=.152, length and image ability F= 1.23, P= .298 and frequency and image ability F= .505, P= .480.
Analysis of the descriptive statistics for reaction times and word length show AM to be slow at reacting to all words, reacting to short words faster than medium or long length words with mean reaction times of 850.2ms, 862.8ms and 1050.1ms respectively. These results demonstrating AM is particularly slow at reading long words. A Tukey's HSD post hoc test was used to look more closely at whether any specific differences are significant between the reaction times and word lengths. The test shows the difference in reaction time is significant between long and short words P= .003 and long and medium length words P= .005 but no significant differences were seen between short and medium length reaction times P= .975. Thus AM is significantly slower at reading long length words compared to short and medium length words.
DISCUSSION
The results from the PALPA battery tests displayed in Table 1 highlight that AM's general ability to read single words when presented individually is not compromised. He obtains maximum scores on tests such as the spoken and written word-picture matching tests highlighting he does not have any damage to his semantic comprehension system.
Scores on tests such as regularity and spelling and non-word reading highlight he maintains the ability to spell and read both words and non-words scoring 27/30 and 24/24 on these tests respectively. He shows no effects of image ability or frequency on his ability to read or spell words as he scores 80/80 on the image ability and frequency reading task and 37/40 on the spelling task. Both scores are above average for a normal control. Scores on letter length reading and spelling tasks are slightly below a normal average by 1 mark which would suggest letter length of a word does effect his ability to accurately read a word but this effect is not great. The results of the letter discrimination in words and non-words on which AM scored 51/60 suggests he is poorer at discriminating letters when they are presented in word form than as single letters. He is however able to pick out the target word when flanked by other words accurately which highlight further his ability to both read and attend to single words.
The computer based test on which AM demonstrated a length effect significant for long words is somewhat unusual and suggests AM is letter by letter reading in order to read single words. This is a sign of pure alexia and thus suggests that pure alexia can occur due to attentional problems as well as the other more frequently reported causes. The results of the computer based assessment taken with the results for single letters presented in the previous section suggests AM does not show an attentional effect at the level of single letters or words although perhaps an effect would be seen on implementation of a time pressure to the task.
Overall the experiments carried out to look at AM's single word reading abilities suggest he is able to read words accurately when presented alone although he is somewhat affected by the length of a word finding it increasingly difficult once it gets to be long consisting of 6 or more letters. Although AM maintains the ability to read single words accurately an attentional deficit must occur at this level in some form causing him difficulty in attending to just a single word. This is shown in his average time of 7 minutes and 38 seconds to read the words extracted from the paragraphs which is significantly slower than the controls who took on average (?) to read the same word list. Thus AM is troubled by attentional problems to a small degree at the single word level, finding it more difficult to read and discriminate single words in comparison to single letters.
SET OF EXPERIMENTS 3
On the finding of greater problems reading single words in comparison to letters the reading problems and attentional deficit which was becoming apparent was further investigated looking at sentence reading.
METHOD
The experiment used in order to look at sentence level reading looked at the ability to read the sentences which had been extracted from whole paragraphs of text and were presented in the previous section as single words. The sentences were extracted from the text and presented in both trials in size 12 print and Times New Roman font. Both texts were different. The first which made up the first trial consisted of 192 words which made 10 sentences and the second making the second trial consisting of 158 words which made up 7 sentences. AM as well as 6 age matched controls were presented both sets of sentences on separate trials and the accuracy as well as time taken to read from the first sentence through to the last was measured and times recorded using a stop watch for both trials.
RESULTS
The results of AM's sentence reading showed he was able to read the words accurately when presented as sentences however the words were read slowly. It took AM a total of 4 minutes to read all the sentences in the first trial and 3 minutes and 52 seconds to complete reading all the sentences in the second trial. These times are very slow compared to the controls who took on average (?) on trial 1 and (?) on trial 2.
DISCUSSION
The results suggest AM's reading ability is further impaired when required to read a string of letters in the form of a sentence. The considerable time taken to read these sentences suggests AM is finding reading slow and effortful despite being able to read the sentences. The time taken suggests problems at the attentional level as he is able to read the words but lacks the ability to read consecutive words as sentences fluently but reading each individual word carefully before moving to the next. This suggesting due to attentional difficulties he lacks the ability to track the positions of the words on the page making it difficult for him to read and follow the content of the text which he reports an inability to do.
SET OF EXPERIMENTS 4
The tests progressed to looking at AM's reading of paragraphs in order to analyse his reading ability at this level 2 tests were given.
METHOD
Firstly AM was presented a flanking task in which he was required to locate the underlined target word amongst a small group of words which could be described as resembling and small paragraph. Three lines of words were presented in each trial of which there were 24. Amongst each group of 3 lines of words was a target word. All words were three or four letters in length and unassociated as far as possible. In each of the three words lines were five words. The trials were divided up so that in eight trials the target word was positioned in the centre of the top line in 8 it was positioned in the centre of the middle and in 8 the bottom. In each group the target was always in the centre flanked by two words either side of it. The position of the word in the top, middle or bottom line was alternated randomly throughout the trials.
Secondly AM was given the paragraphs from which both the sentences and sigle words had been extracted in the previous tests. The paragraphs were presented in their original form from the newspaper but were separated so as not to read as a full text. Trial one consisted of paragraphs form one article and the paragraphs were presented only after the single words and sentences had already been read. In trial two which consisted of paragraphs taken from a different article the paragraphs were presented in the same way as in trial one apart from the difference in the paragraphs being presented before the sentences or words. The time taken for AM as well as 6 age matched controls to read the paragraphs of which there were three in both trails was measured using a stopwatch from start to finish.
RESULTS
AM identified the target correctly in every trial on the three lines flanking task scoring a maximum 24/24. AM was also able to read the paragraphs accurately in both trials, although the time taken to read the paragraphs in each trial were very slow in comparison to the average time taken for the age matched controls. AM taking a total of 5 minutes and 4 seconds to read the 3 paragraphs in trial 1 which is (?) times slower than the average control time of (?). On trial 2 it took AM 5minutes and 26 seconds to read the 3 paragraphs which is (?) times slower than the average control time of (?).
DISCUSSION
These results demonstrate that AM's attentional deficit is not significant enough to impair his ability to locate, attend to and pick the target word from an array of words as he scores a maximum 24/24 on this task.
His timed reading of paragraphs does however demonstrate a deficit at some level of the attentional mechanism. The times taken illustrate that although his attentional deficit is not severe enough to prevent him from reading the paragraphs completely he has an attentional deficit at some level causing him to read so slowly compared to the controls as he has difficulty tracking the position of the words on the page making the reading of paragraphs difficult as there are several lines of words on the page which compete for AM's attention resulting in his slow and effortful reading.
SET OF EXPERIMENTS 5
The final experiments carried out to complete the analysis of AM's reading difficulties looked at his ability to read and locate words at a whole text level.
METHOD
Prior to the tests looking at single word, sentence and paragraph reading AM was given the text used in trial 1 as a whole. AM was presented the text in the form of a newspaper article. He was required to read the article aloud as far as he could and to report the place in which he could no longer follow the text. It was from analysis of results obtained from this text reading which led to the development of the tests presented previously separating the texts into their paragraphs, sentences and single words.
A second test using a whole text was developed in order to demonstrate and investigate AM's attentional difficulties as found in the map search task from the test of everyday attention, but to make this attentional test specific to reading. A test was thus developed in which a text containing a total of 526 words was presented in its true form as a newspaper article. The words teacher or teachers and pupil or pupils appeared in this article a total of 22 times. The text was placed in an A4 size transparent pocket file and AM as well as 6 age matched controls were given 2 minutes in which to read the text and highlight using a red marker pen the target words when located in the text. A maximum time of 2 minutes was allowed to locate the words or when if before 2 minutes the participant thought they had located all the target words this was the time recorded.
RESULTS
AM was able to read only the first 4 lines of the text accurately before reporting the 5th line as merging and becoming indistinguishable from the remainder of the text.
AM's score on the word search task was 7/22 after the full 2 minutes of allowed time. He also made 2 errors in this time. This result is clearly abnormal compared to the results of the age match controls whose scores and times can be seen in table 2.
Insert table 2
DISCUSSION
AM's ability to read whole texts is clearly impaired evident from his ability to only read 4 lines before reporting difficulties. It is clear that as he is able to accurately albeit slowly read text when presented as paragraphs (as presented in the previous section) that as the length of the text increases so does his difficulty thus suggesting that his attentional deficit is worse when there is more in the visual field to follow and attend to. His attentional deficit with full text is further demonstrated on his poor score in the word search task further demonstrating his difficulty in attending to words positioned on a page resulting in the apparent merging of the sentences and loss of ability to follow the text and thus read accurately.
GENERAL DISCUSSION
Analysis of the results obtained from the testing of patient AM indicate difficulties reading are being caused by an attentional deficit in the form of attentional dyslexia. Deficits shown by AM in some cases correspond with deficits reported in attentional dyslexic cases in the literature. For example Saffran and Coslett (1996) describe the patient NY as having a marked disparity between his reading of single words which was well preserved in comparison to his ability to read text. AM has also shown this effect in his reading being clearly able to read single words when presented individually but struggling on introduction of large pieces of text. This being one indicator linking AM's symptoms to that of those reported in previous cases of attentional dyslexia. It is also reported in case NY that he reports having stopped trying to read altogether due to the words "running together" (Saffran and Coslett, 1996). This is the same complaint made by AM leading to the downfall of his reading ability.
The correspondence of AM's deficit with that of patient NY (Saffran and Coslett, 1996) as well as the clear impairment to his reading ability which has been shown by comparing the reading time of AM to that of age matched controls are both clear indicators that AM is an attentional dyslexic further supported by his reported inability to follow the content of a text even when read at a sentence level, despite his maintained ability to read both sentences and paragraphs accurately albeit slowly. This suggests AM's attentional deficit is not as severe as the majority of cases previously reported as he is able to read text at sentence and paragraph level, although an inability to follow the content of this text alongside the time taken for AM to read such text in comparison to age matched controls suggests AM's reading is very slow and effortful due to difficult with his attentional system.
For example AM's attentional dyslexia can be by no means as severe as those patients reported by Warrington and Shallice (1977) who were impaired on a flanking task as early as picking a single target letter from an array when flanked, a task which AM had no apparent difficulty doing. The same difficulty in distinguishing flanked letters was reported by Warrington et al. (1993) in the case of patient BAL. Furthermore AM does not appear to make migration errors frequently. These errors are reported in the literature as a common consequence and sign of attentional dyslexia and are reported and discussed in the cases of both NY (Saffran and Coslett, 1996) and FL (Mayall and Humphreys, 2002). The only time in which AM has shown evidence of migration errors in the tests carried out was in the case of the 2 errors which he made in the letter naming task, these errors resembling migration errors. It is however possible that with further analysis of AM's reading these errors would be seen more frequently. This being a possible area for further investigation which may help to further support the proposition that AM shares the characteristics and is therefore suffering at some level from attentional dyslexia.
AM's attentional problems seem to be generalized to things in the visual field, evidence for this is provided by AM's good performance on the auditorily presented lottery test taken from the tests of everyday attention. The apparent generalisation of this attentional deficit to the visual field provides support for a proposed argument that the brain does not accommodate a region specific for the use of reading but a more general area of the brain exists which is used for reading as well as other types of visual processing.
AM's deficit is not specific to reading but more generally to the visual field and this is supported by his poor score on both the map and telephone search tasks taken from the tests of everyday attention, which required more general use of the visual system aside from reading.
The argument concerning the existence of a general area of the brain responsible for visual processing stems from research by Behrmann et al. (1998) that alexia which is often described as pure alexia as impairment was in recognizing and identifying orthographic material sparing other visual and cognitive abilities is not in fact pure.
Phonological dyslexia is an impairment in which patients are able to read real words accurately but are significantly impaired at pronouncing legal non-words. This disorder which is also known as pure alexia is argued to result from impairment to the rule governed grapheme - phoneme procedure which can also be called the assembled spelling route which is highly specific to reading (Coltheart, 1985., and Funnel, 1983).
Behrmann et al. (1998) based this argument on evidence from 17 phonological dyslexic patients who were found to exhibit a more general phonological deficit on evidence obtained from non - reading phonological tasks which required blending or segmentation (Berndt et al., 1996., and Farah et al., 1996., and Patterson). The data obtained from these 17 phonological dyslexics performance on this test suggested a reading deficit arising from impairment to a general phonological area rather than one specific to reading ability as previously suggested in the case of alexia.
Similar findings to this have also been reported in research looking at other types of acquired dyslexia. For example surface dyslexia which has in the past been attributed to damage to the whole word or direct route of reading printed words (Coltheart, 1982., Coltheart et al., 1983., and McCarthy and Warrington, 1990). Has more recently been by Patterson et al. (1992) to a more general deficit in semantic memory and that semantic knowledge is required in order to retrieve phonology for irregular items. Support for this proposition can be taken from evidence that although regular and exception word reading deteriorates with increasing semantic impairment, the decline is sharper for exception words thus suggesting surface dyslexia is a consequence of a general cognitive ability deficit (Patterson et al., 1994., and Strain et al., 1998).
To provide further support for the position that a generalized visual area exists in the brain, not specific to reading Behrmann et al. (1998) carried out a study looking at more fundamental perceptual problems in alexics other than just reading. Behrmann et al. (1998) used 48 year old alexic patient EL to successfully demonstrate that a single pure alexic reader was also impaired at picture identification across a large set of stimuli with the reaction time taken to identify the pictures increasing disproportionately relative to control subjects as visual complexity increases (Behrmann et al., 1998, p 1117). This finding was later confirmed when on testing a larger group of pure alexic patients the same results as seen in EL were seen.
Thus this research demonstrated that patient EL had a more fundamental perceptual problem which resulted in letter - by - letter reading as well as impairment to picture processing. This deficit can not be argued to be due to a larger brain lesion covering other areas of the brain including that specific to reading as tests on other alexics provided the same results as found in EL. Behrmann et al. (1998) therefore argue that this is evidence that pure alexia is not pure as it is not a deficit affecting a reading specific area of the brain alone but a more general - purpose cognitive mechanism exists and it is damage to this which results in alexia. They also argue that because reading is a relatively knew cognitive ability in evolutionary terms it makes sense for it to be "mediated by a neural substrate that sub serves other visuoperceptual functions and thus a general purpose system has been recruited in order to mediate this processing of the alphanumeric symbols required for reading" (Behrmann et al., 1998., p 1127).
The evidence presented in this report of patient AM provides further evidence for this position from the point of attentional dyslexia. AM demonstrates a general attentional deficit in visual perception not specific to reading suggesting further that a more general visuoperceptual area exists in the brain which accommodates but is not specific to reading.
This investigation has ultimately found AM's reported reading and more general visuoperceptual difficulties to be resulting from a disorder known as attentional dyslexia. AM's attentional dyslexia is not severe in comparison to other reported cases (Warrington and Shallice, 1977., and Warrington et al., 1993) but it is damaging enough at its level to cause AM to experience difficulties reading whole texts and understanding what he is able to read at a sentence level, as well as problems of a similar nature in following visuoperceptual stimuli other than written words, including pictures and other types of shapes as well as the capacity to attend to and follow the plot of a detailed television programme or film.
These problems of attentional dyslexia are likely to result from damage to AM's left occipital lobe due to damage from the stroke suffered leading to the development of vascular dementia. Damage to this area of the brain has impaired AM's visuoperceptual centre which allows him to read as well as attend to other visuoperceptual stimuli accurately. Damage to the attentional mechanism in this area of the brain has meant that AM has difficulty distributing his attention between items in a visual array, therefore in the case of reading for AM the position of words in a text on a page get mixed up and appear to merge together as AM's damaged attentional mechanism doesn't allow him to track the position of the words on the page thus leading to difficulty in both reading and comprehending what can be read as the attentional window which would allow AM to focus on and understand each consecutive word in a text has been damaged. An abnormally wide attentional window could result in a loss of location information allowing in severe cases of damage letters to drift between words but in the less severe case of AM, words just drift between words with their individual letters remaining in place. The drifting of these words causes the apparent appearance of sentences merging together resulting in AM's reading difficulty. It does however seem from AM's preserved ability to read both sentences and paragraphs accurately albeit slowly that AM's attentional dyslexia is not only mild but he maintains the ability to attend to stimuli short in length, suggesting the greater the interference and number of potential objects to attend to in the visual field the greater AM's difficulty in attending to the target stimuli, resulting in his attentional deficit which characterizes his attentional dyslexia.
REFERENCES
Alzheimer Scotland. (2002). Vascular Dementia-Alzheimer Scotland-Action on Dementia. Website www.alzscot.org/info/vasculardementia.html accessed on 24/03/03.
Behrmann, M., Plaut, D.C., & Nelson, J. (1998). A Literature Review and new Data Supporting an Interactive Account of Letter-by-Letter Reading. Cognitive Neuropsychology, 15 (1/2), 7-51.
Behrmann, M., Nelson, J., & Sekuler, E.B. (1998). Visual complexity in letter-by-letter reading: "Pure" alexia is not pure. Neuropsychologia, 36 (11), 1115-1132.
Berndt, R.S., Haediges, A.N., Mitchum, C.C., & Wayland, S.C. (1996). Why do patients with phonological dyslexia have difficulty reading non-words? Cognitive Neuropsychology, 13, 763-801.
Brown, M.M. (1993). Vascular Dementia. Alzheimer's Review, 3 (2), 57-62.
Coltheart, M. (1982). The psycholinguistic analysis of acquired dyslexias: Some illustrations. Philosophical Transactions of the Royal Society of London B, 298, 151-164.
Coltheart, M., Masterson, J., Bying, S., Prior, M., &Riddoch, M.J. (1983). Surface Dyslexia. Quarterly Journal of Experimental psychology, 35A, 469-495.
Coltheart, M. (1985). Cognitive neuropsychological and the study of reading. In Attention and Performance XI. Posner, M.I., & Marin, O.S.M. Hillsdale, New Jersey, Lawrence and Erlbaum Associates, pp.3-37.
Davis, C.J., & Coltheart, M. (2002). Paying attention to reading errors in acquired dyslexia. Trends in Cognitive Sciences, 6 (9), 359-361.
Ellis, A.W., & Young, A.W. (1997). Human Cognitive Neuropsychology. A Textbook with Readings. East Sussex, Psychology Press Ltd.
Farah, M.J., & Wallace, M.A. (1991). Pure alexia as a visual impairment: A reconsideration. Cognitive Neuropsychology, 8 (3/4), 313-334.
Farah, M.j., Stowe, R.M., & Levinson, K.L. (1996). Phonological Dyslexia: Los of a reading-specific component of the cognitive architecture. Cognitive Neuropsychology, 13, 849-868.
Funnell, E. (1983). Phonological processes in reading: new evidence from acquired dyslexia. British journal of Psychology, 74, 159-180.
Mayall, K., & Humphreys, G.W. (2002). Presentation and task effects on migration errors in attentional dyslexia. Neuropsychologia, 40 (8), 1506-1515.
Mayer, J.F., & Murray, L.L. (2002). Approaches to the treatment of alexia in chronic aphasia. Aphasiology, 16 (7), 727-743.
McCarthy, R., & Warrington, E.K. (1990). Cognitive Neuropsychology. London, U.K., Academic Press.
PALPA
Patterson, K.E. Phonological alexia: The case of the singing detective. In Case Studies in the neuropsychological of reading. Funnell, E. Hove, U.K., Lawrence Erlbaum.
Patterson, K.E., & Hodges, j. (1992). Deterioration of word meaning: implications for reading. Neuropsychologia, 30, 1025-1040.
Patterson, k.E., Graham, N., & Hodges, J.R. (1994). Reading in dementia of the Alzheimer type: A preserved ability? Neuropsychology, 8, 395-407.
Saffran, E.M., & Coslett, H.B. (1996). "Attentional Dyslexia" in Alzheimer;s Disease: A case study. Cognitive neuropsychological, 13 (2), 205-228.
Shallice, T. (1988). From Neuropsychology to Mental Structure. Cambridge University Press, Cambridge.
Shallice, T., & Warrington, E.K. (1977). The possible role of selective attention in acquired dyslexia. Neuropsychologia, 15, 31-41.
Strain, E., Patterson, L., Graham, N., & Hodges, J.R. (1998). Word reading in Alzheimers disease: Crossectional and longitudinal analyses of response-time and accuracy data. Neuropsychologia, 36, 155-171.
Tadd, W. (2002). Vascular Dementia. Website www.uwcm.ac.uk/study/medicine/geriatric_medicine/ageing accessed on 24/03/03.
Test of Everyday Attention
VOSP
Warrington, E.K., Cipolotti, L., & McNeil, J. (1993). Attentional Dyslexia: A Single Case Study. Neuropsychologia, 31 (9), 871-885.
