Language

1. Language • this lecture will examine how written language is processed as revealed by neuropsychological findings • how do people normally read (mostly single words), what occurs when that system is damaged?

2. Language • History • reading impairment resulting from acquired brain damage is called an acquired dyslexia • Dejerine (1892) distinguished two types of acquired dyslexia • alexia with agraphia (an impairment of reading and writing (spelling) • alexia without agraphia (an impairment of reading without a writing impairment) • e.g., Howard Engel, a Canadian mystery writer; Benny Cooperman is the name of his detective

3. Language • Model of syndrome (Dejerine) • centre existed for the processing of visual images of letters that mediated reading and writing • located in the angular gyrus region of the left parietal lobe • when this region was damaged it would impair reading and spelling • when only reading damaged, it was hypothesized that visual areas feeding into this centre were damaged

4. Language • Field of acquired dyslexia changed dramatically with Marshall & Newcombe (1973) publication • this paper investigated the pattern of errors made by dyslexic patients

5. Language • showed that there were two types of patients • one type of patient made grapheme to phoneme errors (e.g., insect ->insist, hard to soft c; incense ->increase, soft to hard c) • grapheme-unit of written language, roughly a letter • Phoneme- unit of spoken language, roughly sound of a letter • described patients making this type of error surface dyslexics • other type of patient made semantic substitution errors (e.g., speak -->talk, sick -- > ill, mud -- > quagmire • described these patients as deep dyslexics • Describe Tom

6. Language • Proposed two-route model of reading • according to this model a written word when read can access its memory representation via two routes -- either directly through its orthographic (visual word form) representation or indirectly through its phonological representation (recall, Posner) • surface dyslexia results when semantic route is damaged • deep dyslexia occurs when phonological route is damaged

8. Language • Types of dyslexia: there appear to be 2 different types of dyslexia: peripheral dyslexias, impairments that interfere with the processing of a word as a word form, and central dyslexias, impairments that occur afterward

9. Language • Peripheral dyslexias • Letter-by-letter reading • Letter-by-letter reading also called alexia without agraphia, agnosic alexia, word-form dyslexia • patients with this disorder read letters much better than words, and appear to read by building up word one letter at a time in a slow, laboured process – describe GM • quantitative data support this hypothesis

11. Language • As Table 4.1 shows • Letter-by-letter readers show a word length effect that is almost linear • in addition, letter reading errors appear to be correlated with the time to read words • further results show that letter-by-letter readers find it much more difficult to read words that are written in script • also, accuracy performance decreases if exposure duration is reduced

12. Language • Results suggest patients with alexia have to use an explicit letter-by-letter process in order to read a word • theoretical question: is letter-by-letter reading a consequence of a perceptual deficit that is limited to the processing of written stimuli or is it a more general deficit • if the deficit is specific this would suggest that there are perceptual modules that are specific to the reading process (this issue is unresolved currently)

13. Language • Evidence appears to favour the hypothesis that letter-by-letter reading is a consequence of a specific impairment • letter-by-letter reading however, appears to be a compensatory strategy, rather than a feature of normal reading. Therefore, understanding letter-by-letter reading may provide little insight into the cognitive processes underlying normal reading • put another way, letter-by-letter reading does not reflect a reduced set of normally operating processes

14. Language • What is impaired in letter-by-letter readers? • Standard hypothesis is that there is a deficit in the processing of orthographic information? • To test whether the alternative hypothesis that the deficit might be in the naming of the word, Patterson & Kay (1982) showed words briefly (for 2 sec) and then had letter-by-letter readers make categorical judgements. Results showed that subjects were unable to make categorical judgements for words that could not be read immediately

15. Language • Two similar models of letter-by-letter reading have been proposed by Patterson and Kay and by Warrington and Shallice • note: in both models compensatory processes are hypothesized

17. Language • Surface dyslexia • surface dyslexics appear to have difficulty mapping graphemes into phonemes (letter combinations into sounds) • characterizing the grapheme to phoneme failures • assigning inappropriate sound when grapheme is ambiguous or depends on context (e.g., insect ->insist (hard to soft c); guest -> just (hard to soft g) • assigning a phonetic value to a soft grapheme (e.g., listen -> liston • failing to apply the rule of e (e.g., bike -> bik) • reading one letter of vowel digraph (e.g., niece ->nice)

18. Language • Surface dyslexia • other errors • stress shift errors: begin -> beggin • regularization errors: gone --> goan; pint --> pint with a short I • insert Table 4.3 here • Lint, flint, mint, pint, (note: sint) • Other irregular words yacht • In addition, to being a letter-by-letter reader, GM had surface dyslexia

21. Language • Summary: Peripheral dyslexias • appear to be two distinct types of peripheral dyslexia • alexia without agraphia • surface dyslexia • alexics appear to have damage to the word-form recognition system, and use a letter-by-letter processing strategy to compensate • surface dyslexics may have damage to a system that translates graphemes into phonemes

22. Language • Central dyslexias • Warrington has shown there are patients who can read fluently phonologically and yet do not have semantic knowledge of the words that they are reading • note: these patients appear to be able to read irregular words fairly well also • these were patients with Alzheimer’s disease (AD)

24. Language • Central dyslexias---spared phonological reading • Bub (1985) in a careful study showed that although patient MP could read irregular words aloud, she was unable to understand their meaning • e.g., on the Peabody test of word comprehension she scored at the level of a 2.8 year old child • in a word-word matching test - select an associate of the target from among 4 items, she scored at chance (chair, apple, buy, pen: table)

25. Language • Central dyslexias---spared phonological reading • Thus, these data suggest that it is possible to access a phonological output representation of a word without being able to access the semantics of the word • insert Figure 5.1 here

27. Language • Central dyslexias--spared phonological reading • one way to account for this result is to assume that visual input can be mapped into phonological output without entering into semantic memory • see Figure 5.1

28. Language • Central dyslexias--spared phonological reading • as Figure 5.1 shows it is assumed that visual input (a written word) can access a visual input lexicon, which in turn can give rise to a phonological output lexicon without entering semantic memory • alternatively visual input can access semantic memory (via a visual input lexicon) and/or can access the phonological output lexicon

29. Language • Central dyslexias--spared phonological reading (summary) • other models have also been proposed to account for this finding • what is common to each of these models is the idea that visual input can be mapped into phonological output (speech) without having to go through semantic memory

30. Language • Central dyslexias--deep dyslexia • the theoretical importance of deep dyslexia is that it provides evidence that it is possible to access semantic memory via the orthographic route alone, rather than via the phonological route • astonishing phenomenon (e.g., muddy --> quagmire)

31. Language • Central dyslexias--deep dyslexia • types of errors made by deep dyslexics • semantic errors: ill--> sick • visual errors: life --> wife • derivational errors: entertain -->entertainment • effects of syntactic class • nouns more likely to be read correctly than adjectives, which were more likely to be read correctly than verbs, which were more likely to be read aloud than function words (e.g., prepositions and pronouns)

32. Language • Central dyslexias--deep dyslexia • imageability • deep dyslexics are more likely to read highly imageable words than low imageable words • see Table 5.3 for a summary

34. Language • Explanations of deep dyslexia • simplest explanation is that deep dyslexia occurs when there is a relatively intact route from the visual word form to the semantic system, coupled with an impaired route from the visual word form to the phonological system • See, for example Marshall & Newcombe model on next slide

36. Language • Explanations of deep dyslexia • according to this account a visual word form elicits a broad representation of meaning, not a specific specification • specification sufficient to elicit concrete nouns, but not to elicit abstract nouns, function words etc. • Note: studies have shown that cognitively unimpaired individuals are better able to retrieve the meaning of a word from its definition when the word is concrete than when it is abstract

37. Language • Explanations of deep dyslexia • although other explanations of dyslexia have been proposed, it appears that the data support the idea that it is possible to access semantic memory from an orthographic representation without having to access a phonological representation

38. Language • Implications of acquired dyslexias for normal reading • the finding of letter-by-letter reading shows that people with acquired brain injury may develop strategies of compensation that do not reflect normal cognitive processing of visual language • thus, one needs to be careful in extrapolating from performance of brain injured patients to normals because brain-injured performance is not always just a ‘subtraction’

39. Language • Implications of acquired dyslexias for normal reading • taken together the different types of dyslexia support the idea that there are several different routes for reading words • one route permits words to be read without being understood • another route permits visual word stimuli to reach semantic systems without phonological mediation

40. Language • A classic question in the psychology of language concerns the relation between the processes responsible for reading a word and writing a word • Dejerine in his investigations of alexia and agaphia hypothesized that a single centre was responsible for both reading and writing • insert Figure 4.1 here

42. Language • Put more generally, one can ask whether the processes and representations used by input and output systems are the same or different • e.g., reading versus writing; speech perception versus speech production; encoding versus retrieval (memory) • it turns out that this question has proven to be difficult to answer

43. Language • Why is this question difficult to answer? • Insert Figure 7.1 here • Figure 7.1.I represents a common I/O system; 7.1.II represents separate I/O systems • on the common I/O account a patient who has impaired performance at input and output has damage to the I/O system; dissociations between the two systems are accounted for by damage to the input (A) or output (D) systems

45. Language • According to the separate system account similar degrees of impairment will occur when both systems are damaged, whereas dissociations between input and output are a reflection of selective damage to one of the I/O modules • one pattern of performance that does appear to be difficult to account for in terms of the common I/O account is finding that some patients are impaired in their ability to repeat words (conduction aphasia)

46. Language • Conduction aphasia . Patients have relatively well preserved language comprehension and language production, but are impaired in their ability to repeat words . Preserved speech comprehension suggests that the pathway into the input system is relatively intact; likewise preserved speech production suggests output system and speech is preserved . Single i/o system would have to predict no impairment of word repetition

47. Language • Another approach that has been taken to finding evidence for separability of input and output systems in reading and speaking has been to use a dual task paradigm • the logic of using dual task is as follows: • two routine but demanding tasks can be performed well simultaneously if they are carried out by two separate functional subsystems (recall automaticity requirement)

48. Language • It follows from this that if there are separate input and output systems, performance should be relatively well preserved under dual compared to single task conditions provided the two tasks engage different input and output systems • In contrast, performance should deteriorate if the two tasks engage the same input or the same output systems • Shallice, McLeod, and Lewis (1985) performed an experiment in which subjects performed tasks alone or concurrently

49. Language • reading aloud (read and repeat words aloud) • Visual input ortho input phonological output system (NOTE: no semantic analysis) • Word detection (listen to words and detect name) • Auditory input phono input  semantic system • Reading aloud + word detection • Two tasks are rel. independent, and hypothesized to use different input and output systems. Hence there should be little interference. This result was obtained as shown in Figure on next slide

50. Language Read + name detection – little interference (diff. i/o systems) Read + syllable count – interference (same o/p system) Shadow + name detection – interference (same i/p system) Aud. = Auditory; Phon. = Phonological