Dyslexia

Question 1

Magnocellular theory

Answer 1

John Stein et al. Biological underpinning. There are deficits in the magnocellular cell systems of the visual and auditory cortex. (in areas V5). It affects vergence control of eyes and letter jump around. The deficits in the brain cause them to not let the eyes focus on visual information so it is the perception of the letters that is difficult. There are some reports of coherent motion processing difficulties in dyslexia but inconsistent evidence. Many dyslexics do not have this problem. The magnocellular pathway is impaired in other developmental disorders that do not come with poor reading. Motion detection deficit seems to be a consequence of reduced reading practice in dyslexia. This theory offers no explanation for the phonological deficits seen.

Question 2

Coherent motion task

Answer 2

Goswami (2015) The child has to detect the direction of motion in a dense array of moving dots.
Motion - lots of dots moving but there is a majority motion.
Static - control display where all the dots are not moving apart from the ones that are going in the direction of motion.
They saw an activity change in V5 in response to these motion tasks. A difference in activation between when the dots are moving and when they are static. Also if people undergo reading intervention, there is a change in activity in the V5 area as well. Reading intervention has an effect on motion detection so the perception of motion and reading are connected.

Question 3

Visuo-spatial attention deficit theory

Answer 3

Facoetti et al. There is a deficit in visuo-spatial attention causing sluggish attention shifting. They have slow attentional disengagement from stimuli so this affects letter decoding. When reading, we need to be able to switch our attention from one word or letter to the next very quickly so if there is a deficit in this, it will severely impair reading. The data for this theory is mainly coming from Italian which has a very shallow orthography. It hasn’t really been identified by other researchers. There are also causal issues as dyslexics may have attention shifting issues because they read less as attention shifting is a skill gained from reading.

Question 4

Accuracy target detection

Answer 4

Goswami (2015) found individuals with dyslexia require longer cue intervals for successful cue utilisation. Cue on one side that is indicating where the stimulus is supposed to appear later either validly or invalidly. More of the cues will be valid than invalid. Dyslexics found it harder to utilise the cues to predict the target location. They may need a longer cue to indicate where the target is as they shift their attention from the cue to the target slower.

Question 5

Auditory theories

Answer 5

Tallal et al on phoneme level and Goswami et al on syllable level. There must be deficits in basic auditory processing mechanisms that contributes to the development of well specified phonological presentations. This is a dominant theory. There is general agreement across languages that phonological difficulties are ubiquitous. Evidence for different types of auditory processing impairments in dyslexia. However, there is patchy literature and too much data is from adult developmental dyslexics.

Question 6

A deficit in phonological representation

Answer 6

Phonological representations of lexical items are indistinct, underspecified and incomplete

Question 7

Phonological awareness tasks

Answer 7

Dyslexic children have consistently lower performance in phonological awareness tasks. There are differences in phonological awareness across languages. English is a more orthotopically challenging language, the phonological deficits are seen to be much greater in dyslexic children there. Greek is a very shallow orthographical language so performance is much better.
Porpodas - Greek 6 year olds, 78% correct in dyslexics and 98% correct in RL controls
Wimmer - German 10 year olds, 86% correct in dyslexics and 86% correct in RL controls
De Gelder - Dutch 11 year olds, 61% correct in dyslexics and 83% correct in RL controls
Bruck - English 8-15 year olds, 47% correct in dyslexics and 72% in RL controls

Question 8

Nonword reading In German and Greek

Answer 8

Porpodos and Wimmer. Tested nonword reading ability and speed. Controls matched at age so their reading level is probably much higher than dyslexic children. For Greek, the dyslexic children are actually really accurate in their reading, nearly as good as controls. Age matched controls are the same across countries in their reading ability but dyslexic children are not. Difference between control and dyslexic is pronounced across the countries. German is slightly harder in its orthography which is maybe why the performance is not as good. Greek children might be more accurate but they are just as slow as German. Dyslexic children read notably much slower than the age matched controls.

Question 9

English vs German speaking dyslexics

Answer 9

Landerl et al (1997) Reading level controls are about 4 years younger than the dyslexics. This means dyslexics are reading at levels nearly 4 years below their actual age so a 4 year gap between their ability and the age controls ability.
Reading nonwords:
English dyslexics have a much higher error rate. The longer the words (the more syllables it had) the more children specifically the dyslexics struggled. English read slower and make more mistakes on average. Dyslexics read slower in English than controls. Dyslexia in English may be more severe.
Low vs high frequency words:
German and English are similar. They had about a 10% error rate for high frequency and 50% error rate for low frequency.
Spoonerism task:
Requires onset-rime recombination. They are asked to exchange consonantal onsets so exchange the word beginnings. This requires good knowledge of phonemes. Performance is poor in both German and English dyslexics so the phonological problem is present in both languages. Even the controls made some errors so this task is not easy for children.

Question 10

The effect of orthographic complexity on dyslexic reading ability.

Answer 10

Landerl et al (2013) looked at children ages 8 to 12 across 6 languages. Assessed:
IQ reading - read as quickly as possible without making mistakes
Phoneme deletion - say a word without one of the phonemes, this is all about the ability to manipulate phonemes
Rapid automized naming (RAN) - sequentially name as quickly as possible something, this is all about accessing phonetic representations in long term memory rapidly
Verbal memory - digit span forwards and backwards, this is assessing the ability to keep and manipulate phonological and semantic information in the mind
For each z point decrease in the independent variable (the above things we are measuring) the probability of being dyslexic multiplies. Phoneme deletion is the best predictor of dyslexia. Digit span is a less good predictor. Direct phone manipulation is shown to be a good predictor of dyslexia. More differences between languages on phoneme detection task the RAN task. This shows it’s the phonemes that make the biggest differences between the languages and maybe what’s making the biggest difference in dyslexia.

Question 11

Phenotype of dyslexia across languages

Answer 11

Shallow/transparent orthography:
- accuracy deficit only visible initially
- later usually speed is the issue rather than accuracy
Deep/opaque orthography:
- accuracy have the potential to improve
- accuracy and speed problem may be persistent
Slow reading speed is the problem in any case. Reading is inefficient and not fun. They have less self elected practice so they are not reading books for fun. School materials require a lot of reading so maybe why they struggle in school. But diagnostic frequencies depend on the criteria in a given country.

Question 12

Phenotype of dyslexia in English

Answer 12

Normal non-verbal IQ. Low reading accuracy and speed. Poor phonological recoding so there is a deficit in nonword reading.

Question 13

Developmental linguistic hierarchy

Answer 13

• Stressed syllables
• syllables
• onset-rime
• phonemes and graphemes
  There are different theories about where in the developmental linguistic hierarchy the origin of the deficit is.

Question 14

Sound waves

Answer 14

Frequency - number of full cycles per unit of time. 1 Hz = 1 cycle per second.
Period - the time of a full cycle
Amplitude - how hight the wave goes from baseline 0
Phase shift - where the initial starting point of a wave is changed in time.

Question 15

Spectrogram

Answer 15

Goswami (2015) You can represent speech in terms of its frequency contents and can identify speech in terms of its frequency components. Spoken information can be shown in frequency changes, energy changes along various frequencies as a function of time. Each phoneme can be represented by its formants.

Question 16

Modelling the time varying speech signal

Answer 16

Speech rhythm and the amplitude envelope. Frequency content as a function of time. Continuously changing. Can represent all of this in terms of the amplitude of speech, how the intensity of speech changes as a function of time.
Amplitude modulation - prosody, rhythm
Cochlear implants - transmit envelope only

Question 17

Where is the phonology in the speech envelope and fine structure

Answer 17

Systematic amplitude modulation structure in the envelope. According to the phonological theory, the major disruption in dyslexia would be in the detection of the speech envelope. So how well dyslexics brains will be able to track the overall energy content of speech. How overall amplitude of spoken speech changes carries a lot of information e.g. stress pattern information, where are the stressed syllables, where are the individual syllables. There are continuous changes in the speech envelope so being able to track these is crucial for tracking speech continuously. Fine structure of speech are the higher frequency changes in speech related to very fast changing phonetic information.

Question 18

Babies begin with speech rhythm

Answer 18

• auditory signal
• visual dynamics
• motor rhythm
• neural encoding via oscillatory (rhythmic) entrainment
  The idea is that our brains are tune to detect this speech rhythm from very early on. So rhythmic perception of speech provides very important cues for accessing phonological information. Rhythmic perception relies on lot of cues to get phonological information.

Question 19

Levels of analysis

Answer 19

Cognitive - phonological difficulties
Sensory - rhythmic difficulties
Neural - How does the brain encode rhythm
For dyslexia, the core difficulty is in recovering prosodic (rhythmic) structure from the speech signal.

Question 20

Prosody

Answer 20

Patterns of stress and intonation in language

Question 21

Brain firing is rhythmically coordinated

Answer 21

The brain encodes rhythm in the form of neural oscillations. Neural oscillations are periodic changes in neural activity or periodic changes in measured amplitude of neural activity changing around a mean point.

Question 22

Phase locking and reset of oscillations

Answer 22

Phase locking of oscillations is hierarchically organised. At the onset of speech signal, amplitude rise times cause phase reset which is an automatic sensory neural process. When we listen to speech, our brain tracks this information through neural oscillations. Neural oscillations reset the phase. Reset the phase anytime some important stress pattern is encountered or any time some major speech cue in encountered. Phase reset is an important mechanisms in tracking speech.

Question 23

Oscillatory sensory processing by the brain

Answer 23

It is based on sampling energy in the environment. Perception is not continuous, it takes snapshots of the signal. From auditory signals, the brain samples different temporal rates concurrently, this is called multi time resolution.

Question 24

Temporal sampling theory

Answer 24

Goswami (2011) Faster or slower frequencies correspond to tracking stress information, syllable information or phoneme information.
Delta (2Hz) - syllable stress
Theta (5Hz) - syllable
Beta/low gamma (20Hz) - onset rhyme detection
Gamma (35Hz) - phonemes and graphemes
Rise time perception and phase locking to slower modulation is impaired in dyslexia. According to this theory, the disruption in dyslexia is the disruption in the delta networks in the brain. Dyslexic brains struggle to track overall stress information from speech as they put the emphasis on phoneme recognition. They are giving a causal explanation of disruption of reading efficiency in dyslexia.

Question 25

A cross language approach

Answer 25

Brains are the same across languages, orthographies are not. Biological underpinnings of dyslexia are similar across languages. manifestations of dyslexia will vary systematically with orthography.