Day 4 Lecture notes – Reading
The Nature of Cognitive Models
Cognitive models delineate the stages involved in any mental activity. Take object naming.
In order to do this we have to go through a number of stages. We have to see/recognise the
object, we have to understand it, we have to access the spoken word form and then
articulate the word. These stages can be expressed in terms of a simple model:
The model is ‘true’ in as much as it accounts for observed patterns of behaviour. For
example we all occasionally forget words (particularly the names of people). Often we know
all about the meaning of the word (eg we can describe the person, what they do, where they
come from etc), but cannot think of the phonology. This is consistent with the above model.
It suggests that we have processed as far as semantics, but can’t get to phonology.
People with language problems following stroke (aphasia) experience such word finding
failures much more frequently than people with intact language. Nevertheless, we can still
see their difficulties as a derailment of the normal stages of word retrieval. Thinking about
where the chain of processing is breaking down should give us new insights into their
problems and help us to select an appropriate therapy.
When cognitive models were first formulated little attempt was made to relate them to brain
structures. It was stressed that models were purely abstract representations of mental
functioning. With the advent of more sophisticated imaging techniques, there has been a
greater attempt to relate the processes delineated in the models to actual brain regions (eg
see Hillis and Tuffiash 2002).
Universality
One important assumption about models is that they are basically the same from person to
person. In other words, my language system works along the same principles as yours.
This means that we can use evidence from individuals to draw conclusions about how
humans generally process language. Despite this, there is a lot of controversy about the
structure of models and a number of different architectures have been proposed. The model
described in these lectures is just one of many options, although it is one that is widely
applied in aphasia therapy.
Modularity and the Effects of Brain Injury on Cognitive Models
The model introduced here will consist of a number of processing components, or modules,
each of which is responsible for a particular task. This is an important principle. If reading is
accomplished by different modules brain injury may result in some modules being impaired
and others still being intact. In other words, a deficit need not be all or nothing. This is good
news for therapists, in that intact modules offer potential resources for improvement. It also
means that one of our tasks, as therapists, is to find out which components of the system are
impaired and which (relatively) intact.
A Simple Reading Model
What processes are involved in reading aloud a single word? Clearly the first stage is to
analyse the individual letters and their order -the 'Visual Analysis System'. This system must
be able to recognise different letters regardless of handwriting, font or case. This suggests
that the system deals in abstract letter identities, rather than set visual templates.
Having worked out the letter string, the reader has two options available. One is to read the
word aloud using 'phonics', the other is to use a whole word approach.
Let’s take 'phonics' first. This method converts individual letters or groups of letters into
sounds. This has been termed 'Grapheme to Phoneme Conversion' and is shown on the
model as one of the possible reading routes (The GPC route is also sometimes termed the
sub-lexical route or Orthography to Phonology Conversion). This route has to do a number
of things. First of all it has to break up the word into graphemes: ship = sh
i
p
Then each grapheme has to be linked to a phoneme:
sh
/∫/
i
//
p
/p/
Then these phonemes have to be blended: /∫p/.
Supposing this was the only reading route available. You will immediately begin to see
problems. Firstly, the route is dependent upon regular correspondences between print and
sound, eg that 't' is always read aloud as /t/, ‘ch’ as /t∫/. Yet many English words flout these
correspondences. Think about 'mortgage' and 'yacht', and compare 'hint' and 'pint'. Such
irregular words cannot be handled by the GPC route.
A second problem: if this were the only reading route available all words would have to be
understood via their phonology. What about homophones? These are words which share
the same pronunciations but have different meanings (week/weak, gait/gate, air/heir,
pain/pane etc). If we only read via the GPC route we could not tell the difference between
these words.
The GPC route has one strength. This is the only route that can handle novel or non words.
Thus we can use this route to assemble a probable pronunciation for 'brap', even though we
have never encountered this word before.
Reading via the lexical route
Here the product of the Visual Analysis is fed to the Visual Input Lexicon. This might be
imagined as a store of all known words. If the letter string corresponds to an entry in the
store, the word is recognised. Thus this system differentiates between familiar words and
unfamiliar ones (such as foreign words or non words).
The Visual Input Lexicon does not store word meanings. These are processed at the next
Semantic stage. There is huge controversy about the nature of the Semantic (or Cognitive)
system. This will be revisited later in the course. For now, we will say that the system
contains the features that make up word meanings. Thus the word 'cat' would access the
following features: animal, domestic, fur, tail, whiskers, purr, miaow, etc.
Once the word has been processed by the semantic system, it is understood. Of course,
processing often ends here. However, if our aim is to read the word aloud we have to
access its phonology from the next module: The Phonological Output Lexicon (or Speech
Output Lexicon). This is another store, this time of whole word phonologies. A number of
commentators suggest that this lexicon only contains the roots of words (morphological
endings being added by another system).
Our model has a 'Response Buffer' after the POL. This can be imagined as a store that
holds onto the word until it is needed in the speech stream. It is also reasonable to assume
that quite a lot of processing is involved in converting the phonological form of a word into a
phonetic/motor programme. However, this remains unspecified in the model.
Reading Aloud Via Meaning? - The Direct Lexical Route
There is evidence that normal readers access meaning while reading text aloud. For
example, Morton (cited in Ellis 1993) noted that skilled readers tended to make semantic
errors when reading passages aloud, ie they might read 'Saturday' as 'Sunday'. These
errors could only occur if reading was being mediated by the semantic system.
There are also a number of words that can only be read aloud correctly via the semantic
system. For example, in order to pronounce ‘bow’ correctly we need to know whether we
are talking about a bow and arrow or a person taking a bow.
Is it possible to read aloud without accessing meaning? Two sources of evidence suggests
that it is. One comes from people with brain damage. Schwartz, Saffran and Marin (1980)
describe a woman with dementia with a severe deficit in her semantic system. This person
was profoundly confused and could not understand either spoken or written words.
However, she could read aloud well. Crucially, this skill extended to both regular and
irregular words, which confirmed that she was not simply converting written words to sound
using the GPC route (see example below). The only way of explaining her performance was
to argue for a third reading route directly connecting the Visual Input Lexicon with the
Phonological Output Lexicon.
Frequency/ Familiarity Effects
Some words are used a lot (man, car), others more rarely (ram, elk). There are two main
measures of this. One is frequency, which is a count of how often a word appears in a range
of written texts or spoken corpora. The other is familiarity, which is derived by asking
subjects to rate how familiar they feel a word is.
Lexical frequency effects are very powerful and pervasive. For example, high frequency
words are read aloud more rapidly than low frequency ones and stimulate faster responses
in lexical decision.
It seems that the lexicon has an intrinsic bias in favour of common words. This has been
explained by arguing that word entries (eg in the VIL) have different resting levels of activation,
according to their frequency. So a common word like ‘man’ has quite a high resting level of
activation, while an uncommon one like ‘elk’ has a very low resting level. This would mean that
‘man’ only requires a little additional input before it fires (or becomes available), whereas 'elk',
would need considerably more.
Semantic Priming
Several experiments show that reading is facilitated by a meaningful context. For example,
people might be shown the beginning of a sentence followed by a very rapidly presented closing
word. The exposure time needed to recognise the closing word was measured. Closure words
might be consistent with the preceding context, neutral or unexpected. Unsurprisingly, subjects
needed the least exposure time for the consistent words (see Ellis 1993).
Semantic priming is an example of 'top down' processing. 'Top down', is confusing because,
on our model it looks more like 'bottom up'. The term is used because a higher order of
cognitive processing. Let’s imagine that related words are somehow linked together in the
semantic system – possibly because they share semantic features. Thus the word 'dog' is linked
to 'cat', 'lead', 'kennel' etc. Seeing the word 'dog' partially activates these related words. The
feedback route between the semantic system and VIL primes the relevant entries in the input
lexicon. As a result, recognition of one of these entries in a lexical decision task is facilitated.
Imageability effects
Imageable words can be pictured, while low imageability words cannot (as this implies,
imageability correlates very highly with concreteness). Highly imageable/ concrete words (such
as saucepan and tart) stimulate faster responses in lexical decision than low
imageability/abstract words (such as democracy & idea). Synonym judgements, in which the
person has to judge whether two words are similar in meaning show the same trend. These
effects suggest that processing abstract meanings may be intrinsically more difficult than
processing concrete meanings.
Problems in Visual Analysis
Reading difficulties may arise from damage to the system that analyses the letter string (Visual
Analysis). If this is the case, the person may be unable to carry out even very basic tasks, such
as cross case matching:

Are these letters the same? R- r; B- d
or matching letter strings:

Are these the same? BDAQ – bdaq; HMYG - hmyg
We would also expect visual errors in reading, eg LEND read as ‘land’.
Difficulties in visual analysis may arise from a more general impairment, such as visual
hemispatial neglect. Here the person seems unaware of information presented on one
side of space. Neglect most commonly arises after RH damage, therefore neglect
dyslexia usually affects the left side of words.
(Cases of Neglect Dyslexia in the literature: Ellis, Flude and Young 1987; Hillis and Caramazza
1995).
Here are some examples of reading errors made by people with left neglect dyslexia
target word
never
elate
willow
read as
lever
plate
pillow
sad
sadness
sad
badness
n
e
v
e
r
never
Note that the person seems to be aware that there is a letter on the left side of the word, but is
not sure of its identity. In the ‘sad/sadness’ example, the addition of a suffix has ‘pushed’ the
beginning of the word further to the left, which brings about the reading error. In the final
example the word is presented vertically. Now there are no left-most letters, so the word is
read correctly.
Problems in the Visual Input Lexicon
(Example in the literature: Coltheart et al 1983)
What would happen if the person could no longer access entries in the VIL? This would mean
that they could not use the lexical reading routes (ie the semantic route &/or the direct lexical
route). However, if this is their only problem, they could still use the GPC. How would this
manifest?
Regular words are read better than irregular (exception) words
The GPC assembles a pronunciation for a word by using regular letter to sound
correspondences. This works well for regular words, but much less well for irregular words (like
‘yacht’). A reader of English, therefore, will be quite disadvantaged if they can only use GPC.
They may make regularisation errors with irregular words – eg reading ‘yacht’ as ‘yakt’.
Transparent languages, like Spanish and Urdu, have few irregular words. So GPC readers of
these languages will be better off.
Problems with Lexical Decision
The person is shown written words and non words and has to judge which are real words. The
task requires access to the VIL, so will be impaired. If regular and irregular words are tested –
the person may show an advantage for regular items. Why? They can read these items via
GPC, then judge them by using auditory processing. The tester could be sneaky and include
non words which, when pronounced, sound like real words (such as fone). These will be judged
(incorrectly) as being real words.
Words are understood by reading them aloud
The person assembles a pronunciation (via GPC), listens to that pronunciation then
comprehends the word. Therefore, if the person misreads the word (eg because it is irregular)
they will also misunderstand it, eg:
Target word
bear
listen
Read aloud as
beer
Liston
Definition
a drink
the boxer
Homophones may be misunderstood
English contains numerous homophones. These are pairs of words that are pronounced the
same, but have different meanings. A GPC reader will have no means of telling the difference
between these items, eg:
Target word
Read aloud as
Definition
pane
pane
something that hurts (pain)
berry
berry
dig in the ground (bury)
Non words can still be read
The GPC is responsible for reading non-words. Therefore these will be read comparatively well.
A word of caution
Brain damage rarely results in absolute dissociations. Rather we are looking for trends. The
following example is typical:
reading regular words aloud
reading irregular words aloud
30/39
18/39
This person clearly shows a regularity effect in their oral reading (ie regular >irregular).
However, they are not perfect at reading regular words, and they have some ability to read
irregular ones. The latter may indicate that some words can be accessed in the VIL – possibly
because they are very frequent. Despite this, there is a clear over dependency on GPC
reading.
A Note about Terminology
Dependency on the GPC for reading aloud is often termed Surface Dyslexia.
Problems with Grapheme to Phoneme Conversion
(Cases in the literature: Patterson 1982; Funnell 1983; Caccappolo van Vliet 2004)
What would happen if GPC were impaired? If this is the only problem, many aspects of reading
will still be intact, since the lexical reading routes are still available. As a result, the person will
be able to recognise (VIL), understand (access Semantics) and read words aloud (via POL).
However, they will not be able to read non words, as this can only be accomplished by GPC.
They might try to read these items by accessing a similar word in the VIL. This will result in
lexicalisation errors, eg:
Target
Soof
Read aloud as
soot
This form of reading impairment is termed ‘Phonological Dyslexia’.
A problem in semantics
(Cases in the literature: Hillis et al 1990; Hillis and Caramazza 1991)
What would happen if the semantic system were impaired? We would expect difficulties in any
task which requires the person to access word meanings. Furthermore, in our model there is
just one semantic system serving all modalities of language. Therefore we would expect both
written and spoken words to be poorly understood and we would anticipate problems in
production.
Semantic damage is rarely total. Rather, the person often retains a partial knowledge of word
meaning. For example, if they read the word ‘dog’ they may know that this is an animal, but be
unable to access more specific semantic features. This person will make semantic errors in
comprehension testing, eg where the word ‘dog’ is matched to a picture of a cat (but not to an
unrelated item).
Performance in reading aloud will depend upon what other reading mechanisms are available.
Suppose neither the GPC nor the direct route is available, because they have also been
damaged. This means that the person will have to read via their damaged semantic system.
We would expect the following pattern of performance:

the person will make semantic errors in reading aloud (ie reading ‘dog’ as ‘cat’)

reading will be affected by semantic factors; in particular we would expect concrete
words to be read better than abstract words

reading will be affected by grammatical class: eg nouns>verbs (because these classes
differ in abstractness); function words will be poorly read

non word reading will be impossible (as the GPC is unavailable)
This pattern of performance has been termed Deep Dyslexia.
A Problem in the Phonological Output Lexicon
(Cases in the literature: Kay and Patterson 1985; Caramazza and Hillis 1990)
Reading aloud may be impaired by a deficit in the POL. How this manifests will, again, depend
upon what other reading mechanisms are available. Take the case of EST (Kay and Patterson,
1985). Here are some of his test results:




non words were read quite well (67/80)
regular words were read aloud better than irregular words
regularisation errors occurred
lexical decision was good
EST could often define irregular words, even though he could not read them aloud, eg:
thyme
it grows and smells nicely
choir
singing
He could also often match an irregular word to the correct definition:
gauge
the distance between rails of a railway track
a deep valley with steep sides (gorge)
dig something out with your hands (gouge)
What is the story? EST can access the VIL (hence the good lexical decision). He can also
access meaning from written words (hence good performance on the definition tasks). His
reading aloud, therefore, is impaired by access to the POL. GPC mechanisms are still available
(hence good non word reading). If the word is regular EST can therefore use this to assemble a
pronunciation (hence the regularity effect in reading aloud). EST shows that people can depend
on GPC reading for different reasons. Some people may be unable to access the VIL, while
others may have problems at the level of POL.
Letter By Letter Reading (Pure Alexia, Alexia without Dysgraphia)
This reading impairment is difficult to classify. The person can only read aloud by first naming
the letters, eg:
horse
‘aitch .. oh .. are .. ess ..ee … horse’
Unsurprisingly, letter by letter readers tend to be very slow at reading and show powerful effects
of word length (short words > long words).
Letter by letter readers can still write. This lead to the proposal that they are reading via the
spelling mechanism. In other words, they name the letters as if they are spelling the word and
this enables them to identify it.
Can our model account for letter by letter reading? Clearly some visual analysis is taking place
(given that the person can name the letters). However, access to the VIL seems blocked. We
also have to assume that the GPC cannot be used. Some letter by letter readers seem able to
carry out lexical decision with words if they are presented rapidly, ie they are flashed up briefly
on a screen (Coslett and Saffran 1989). This suggests that there may be some covert skills
which do not emerge in normal testing. These skills have also been exploited in therapy
(Friedman and Lott 2000).