dyslexia and the perceptual noise exclusion hypothesis

[Renaissance]

Dyslexia's been mentioned here and there on the board but there's been no specific thread on the topic. I just came across an interesting hypothesis that suggests that performance of dyslexic children deteriorates in conditions of high noise, but when noise is eliminated, children with dyslexia perform at an equitable level as non-dyslexic children.

Here's a couple of studies.

http://www.nature.com/neuro/journal/v8/n7/full/nn1474.html

Deficits in perceptual noise exclusion in developmental dyslexia
Anne J Sperling1, Zhong-Lin Lu2, Franklin R Manis2 & Mark S Seidenberg3

1 Georgetown University Medical Center, 4000 Reservoir Road NW, Building D, Room 207E, Washington, DC 20057, USA.

2 University of Southern California, Seeley G. Mudd Building, Los Angeles, California 90089, USA.

3 University of Wisconsin, Madison, 1202 West Johnson St., Madison, Wisconsin 53706, USA.
Correspondence should be addressed to Anne J Sperling ajs76@georgetown.edu
We evaluated signal-noise discrimination in children with and without dyslexia, using magnocellular and parvocellular visual stimuli presented either with or without high noise. Dyslexic children had elevated contrast thresholds when stimuli of either type were presented in high noise, but performed as well as non-dyslexic children when either type was displayed without noise. Our findings suggest that deficits in noise exclusion, not magnocellular processing, contribute to the etiology of dyslexia.

Behavioral, neuroimaging, computational modeling and intervention studies indicate that mental representations of phonemes are usually impaired in developmental dyslexia1, 2, 3, although the bases of the impairment are less clear. Reading researchers have attempted to identify perceptual, learning or memory impairments that could affect phonological processing4, 5, 6, 7, 8. One prominent hypothesis involves the magnocellular (M) visual pathway4, 5, 7. In some studies, individuals with dyslexia performed more poorly than normal readers on tasks that primarily involve the M channel. However, the evidence for a deficit in the M channel and its linkage to deficits in reading is weak at best, as is true of the temporal processing deficit to which it is thought to be related8. Moreover, many studies that have found magnocellular deficits in dyslexia have used noisy displays4, 5, 7. We investigated an alternative hypothesis based on theories of signal-noise discrimination9: that dyslexia is associated with deficits in noise exclusion. This deficit could explain the impaired M channel processing in studies using noisy displays; however, it also predicts that a similar effect would be found in the parvocellular (P) channel in noisy conditions, and that no deficits would be found in either channel in the absence of noise. We tested this hypothesis by presenting dyslexic and non-dyslexic children with stimuli that were designed to preferentially activate either M or P processes, shown either with or without noise.

The M stimulus consisted of wide bars that rapidly alternated between light and dark. The P stimulus consisted of thinner light and dark bars that did not alternate. In previous research, such stimuli have been regarded as differentially engaging the M and P pathways4, 5, 7. In the no-noise conditions, the pattern appeared to one side of a central fixation mark, while the other side was blank. In the high-noise conditions, noise patches (random bright and dark spots, similar to television static) appeared on both sides of the fixation mark, with the signal pattern embedded in one patch (Fig. 1; Supplementary Methods and Supplementary Videos 1,2,3,4 online). The child's task was to indicate the side that had the pattern. Threshold contrast was determined for each child.

We identified 28 dyslexic and 27 non-dyslexic children (Supplementary Methods and Supplementary Table 1) and obtained informed written parental consent and child assent. Ten dyslexic children also showed broader language impairments. In the no-noise conditions (Fig. 2a), contrast thresholds for dyslexic and non-dyslexic children did not reliably differ for either M (12.3% versus 11.3%, respectively) or P stimuli (16.4% versus 16.4%). In the high-noise conditions, however, dyslexic children's contrast thresholds were significantly (P < 0.05) higher than non-dyslexic children's, in both M (28.7% versus 23.9%) and P (38.3% versus 29.7%) tasks. The high-noise conditions yielded graded effects for both M and P tasks (Fig. 2b), with the language-impaired dyslexic children having the highest thresholds, the non-language-impaired dyslexic children intermediate thresholds, and the non-dyslexic children the lowest thresholds (Supplementary Methods).

Contrast thresholds in both high-noise conditions were correlated with all language measures. In addition, there were moderate correlations with performance on vocabulary, non-word reading and reading comprehension (Supplementary Table 2), and high-noise M threshold accounted for 7.8% of the variance in Exception Word Reading independent of Verbal IQ. When Verbal IQ was co-varied out of the regressions, all correlations (with the exception of high-noise M threshold and Exception Word Reading) became non-significant, suggesting a general link to language, literacy and vocabulary skills, rather than a narrow connection to specific reading measures. Verbal IQ itself is probably strongly affected by noise exclusion deficits, accounting for its relationship to the development of phonological and orthographic skills.

These data parallel findings concerning speech perception, which indicate weaker phoneme boundaries and/or non-optimal perceptual templates in dyslexic children with concomitant specific language impairment10. Both vision and speech data suggest that dyslexia with specific language impairment involves a more severe impairment in noise exclusion than dyslexia alone.

The results are also consistent with findings that poor readers exhibit motion perception deficits only under visually noisy conditions (A.J.S., Z.L.L. & F.R.M., Cog. Neurosci. Soc. 10, D154, 2004), again indicating a potential deficit in noise exclusion, rather than in motion perception (or M channel processing) per se, as previously suggested4, 5.

How might a deficit in noise exclusion affect reading acquisition? One possibility is that the visual impairment does not directly affect reading, but rather is part of a broader problem with noise exclusion that affects other modalities as well (such as speech). The visual deficit may be a marker of a more basic underlying perceptual problem that interferes with the formation of perceptual categories in a variety of domains11, phonological categories being the most relevant to reading acquisition. This hypothesis is consistent with evidence that speech perception is abnormal in infants at risk for dyslexia12.

A second possibility is that the deficit directly affects reading through the visual modality. Letter recognition requires abstracting away from variations in size, font and style; this may be more difficult if visual processing is hampered by deficits in noise exclusion. Failures to form representations that allow efficient recognition of letters and letter sequences would also interfere with identification of word shape and boundaries between words as well as the representation of sequential orthographic structure. Finally, deficits at this level could have detrimental effects on the development of phonological representations, because experience with an alphabet shapes development of phonemic segments13. These effects may not be mutually exclusive; the noise exclusion deficit may be debilitating because it affects reading through several causal pathways.

Our results implicate a perceptual processing deficit in reading and language disorders, one related to noise exclusion rather than anomalies in the M channel or temporal processing. The noise exclusion hypothesis provides a causal theory of the distal neurological basis of dyslexia, via its effects on language development and the acquisition of orthographic and phonological skills.

Note: Supplementary information is available on the Nature Neuroscience website.

Received 24 January 2005; Accepted 4 May 2005; Published online: 29 May 2005.
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Motion-Perception Deficits and Reading Impairment: It's the Noise, Not the Motion

* Anne J. Sperling11Georgetown University Medical Center, ,
* Zhong-Lin Lu22University of Southern California, and ,
* Franklin R. Manis22University of Southern California, and , and
* Mark S. Seidenberg33University of Wisconsin, Madison

*
1Georgetown University Medical Center, 2University of Southern California, and 3University of Wisconsin, Madison

ABSTRACT—We tested the hypothesis that deficits on sensory-processing tasks frequently associated with poor reading and dyslexia are the result of impairments in external-noise exclusion, rather than motion perception or magnocellular processing. We compared the motion-direction discrimination thresholds of adults and children with good or poor reading performance, using coherent-motion displays embedded in external noise. Both adults and children who were poor readers had higher thresholds than their respective peers in the presence of high external noise, but not in the presence of low external noise or when the signal was clearly demarcated. Adults' performance in high external noise correlated with their general reading ability, whereas children's performance correlated with their language and verbal abilities. The results support the hypothesis that noise-exclusion deficits impair reading and language development and suggest that the impact of such deficits on the development of reading skills changes with age.

read full article of above abstract on a pdf file here

 

[mabar]

Thanks Renaissance, I was diagonsed with dyslexia in/since my early childhood and in order to understand myself better, came an impulse to look/read more information/conitive psycology studies about it; I am starting, perhaps in a non distant future I can share/paste the link? here, I am quite ignorant in this themes versus the experience of having it?, still have remains/scars?

 

[Keit]

Thanks Renaissance, I was diagonsed with dyslexia in/since my early childhood and in order to understand myself better, came an impulse to look/read more information/conitive psycology studies about it; I am starting, perhaps in a non distant future I can share/paste the link? here, I am quite ignorant in this themes versus the experience of having it?, still have remains/scars?

SOTT has several articles on the topic of dyslexia, that not only explain the mechanism, but also offer possible ways to deal with it. Just type in "dyslexia" in the search option. Here are some examples:

http://www.sott.net/article/139396-Having-right-timing-connections-in-brain-is-key-to-overcoming-dyslexia
http://www.sott.net/article/196697-Neural-Mechanism-Reveals-Why-Dyslexic-Brain-has-Trouble-Distinguishing-Speech-from-Noise
http://www.sott.net/article/246486-Dyslexic-Childrens-Reading-Improves-with-Wide-Letter-Spacing
http://www.sott.net/article/199254-Dyslexia-Some-Very-Smart-Accomplished-People-Cannot-Read-Well

 

[mabar]

Thanks Renaissance, I was diagonsed with dyslexia in/since my early childhood and in order to understand myself better, came an impulse to look/read more information/conitive psycology studies about it; I am starting, perhaps in a non distant future I can share/paste the link? here, I am quite ignorant in this themes versus the experience of having it?, still have remains/scars?

SOTT has several articles on the topic of dyslexia, that not only explain the mechanism, but also offer possible ways to deal with it. Just type in "dyslexia" in the search option. Here are some examples:

http://www.sott.net/article/139396-Having-right-timing-connections-in-brain-is-key-to-overcoming-dyslexia
http://www.sott.net/article/196697-Neural-Mechanism-Reveals-Why-Dyslexic-Brain-has-Trouble-Distinguishing-Speech-from-Noise
http://www.sott.net/article/246486-Dyslexic-Childrens-Reading-Improves-with-Wide-Letter-Spacing
http://www.sott.net/article/199254-Dyslexia-Some-Very-Smart-Accomplished-People-Cannot-Read-Well

Thanks, I will ... from some articles I read -though do not have much time to post them right now-, is that I stood with the popular belief that dyslexia was a disorder caused by reversing the order of the letters in reading.

 

[mabar]

It has been interesting knowing more about myself from articles, researches, forums, etc … It somehow reconcile part of my history since elementary school being quite difficult, I also began to wear glasses about the same time dyslexia was diagnosed, and when other children were playing at the evening, I was taking extra classes for improving, I have to thank my mother, it was due to her that nowadays I had improve in many things. I think that experiences in my early-elementary life had been hunting me. That is why I tend to look back to find its origins.

Although I must admit that when someone (including her) had told me about my accomplishments, I discarded them (with pain, feeling hurt, I have to work in that issue), every time I was supposed to be like others, being in the media, a some sort of inassolible program, now that I think of it. In relation with this:

Understanding a possible reason why they find something difficult that no one else seems to struggle with may help relieve some of the mystery and negative feelings that many people with a disability feel. Sharing our knowledge of brain research may demystify dyslexia and help students and their parents realize that language processing is only one of many talents that they have and that they are not "stupid," they simply process language differently than their peers.

I think I can say that I am learning to not be stupid. ;) I just process things differently. A nasty program.

These were the articles I read: (perhaps to others may be useful)
Dyslexia and the Brain: What Does Current Research Tell Us? _http://www.ldonline.org/article/14907/

I found interesting this:

Structural brain differences
Studies of structural differences in the brains of people of all ages show differences between people with and without reading disabilities.
The brain is chiefly made up of two types of material: gray matter and white matter. Gray matter is what we see when we look at a brain and is mostly composed of nerve cells. Its primary function is processing information.
White matter is found within the deeper parts of the brain, and is composed of connective fibers covered in myelin, the coating designed to facilitate communication between nerves. White matter is primarily responsible for information transfer around the brain.
Booth and Burman (2001) found that people with dyslexia have less gray matter in the left parietotemporal area (Area A in Figure 2) than nondyslexic individuals. Having less gray matter in this region of the brain could lead to problems processing the sound structure of language (phonological awareness).
Many people with dyslexia also have less white matter in this same area than average readers, which is important because more white matter is correlated with increased reading skill (Deutsch, Dougherty, Bammer, Siok, Gabrieli, & Wandell, 2005). Having less white matter could lessen the ability or efficiency of the regions of the brain to communicate with one another.
Other structural analyses of the brains of people with and without RD have found differences in hemispherical asymmetry. Specifically, most brains of right-handed, nondyslexic people are asymmetrical with the left hemisphere being larger than the same area on the right.

In relationship with this other article: What Causes Dyslexia? _http://www.dystalk.com/talks/86-what-causes-dyslexia (Had not been able to see the video)

Nutrition of The Brain: Contributing to dyslexic problems are problems with the nutrition of the brain. Essential fatty acids (derived from fish oils) constitute around 20% of the makeup of the brain. Unfortunately, nowadays, we eat very little fish. This creates a problem because the essential fatty acids that come from fish oils and are incorporated in the brain are moved in and out of the membranes and other places in the brain, and if you don't replace them then the workings of the brain are impaired and be part of the cause of dyslexia. This is why it is often suggested that people with dyslexic or ADHD problems are actually given supplements of these essential fatty acids.

It is also mentioned here: Can Fish Oils (omega 3s) help Dyslexia? _quote=http://www.dyslexic.org.uk/research-nutrition.html

The DRT has financed many studies that have shown that children with dyslexia, developmental coordination disorder (dyspraxia) or attention deficit hyperactivity disorder (ADHD) or combinations of these can often benefit from taking fish oil supplements. These provide the long chain polyunsaturated fatty acids (LCPUFAs) that make up 20% of the weight of the brain. The omega-3 FAs, eicosapentanoic acid (EPA) and docosahexanoic acid (DHA), can only be obtained easily from oily fish; but they are particularly essential for sharp brain function because magnocellular neurones are especially vulnerable to PUFA deficiency.

Certainly it is something I do not eat much because I do not like it, and the alternatives here are capsules of salmon oil and can sardines, with soy oil which I am avoiding, but I can make a personal experiment and effort and see what happened. Since I do not do well with supplements, so far ascorbic acid had function well, I think I will start slowly, I had sardines for breakfast, I wash out (most) of the soy oil. Certainly the flavor is not within my favorites, but sometimes you (I) do not eat foods because I like it, it is because it does good to the, in this case: brain. Had found entries in this forum about omega3- fatty acids, but had not read them entirely, I will and see how it can be combined.

I also read this one: Four Things All Educators Should Understand About the Dyslexic Brain _http://www.edutopia.org/blog/4-things-about-dyslexic-brain-patrick-wilson

It got my attention because, the four things still happened in my adult life, and I thought, that it was a problem with English language (since it is not my mother tongue, and I used to pretty much hate it -I realized now, that it was a double dyslexic problem, I was in a bilingual elementary school, always in English class a year lower), and it also happened in Spanish language as I recall it nowadays,as having scars from dyslexia. Of course, now that I think of it, it would be a combination of variables.

For example:

1. Writing is a Three-Step Process
Putting pen to paper is a more complicated action for the brain to process than you might think, particularly for dyslexics. It puts huge demands on the short-term memory to move from one step to the next, which can be a real weakness for them. In the brain, the process involves:
1. Synthesizing a thought, e.g., writing a story about what you did last weekend, such as going to the park
2. Working out how you are going to write it: "I . . . ran . . . fast . . . in . . . the . . . park"
3. The physical act of writing; "getting" those words and physically writing them
A dyslexic can typically do one of those things but will struggle to do all of them in sequence. The process of "holding" that thought and then selecting words and subsequently writing them down on paper can end in chaos. Poor sequencing in the brain also makes it very difficult for dyslexics to organize their thoughts and sentences into a structured piece of writing. Creating a structured argument is a bit like cooking while trying to hold all the ingredients at the same time. Sometimes ingredients can fall into the pot in the wrong order. This can lead to a spaghetti soup of ideas that pour out in a stream of consciousness.

Other struggles as automated processes and memory (difficult in recalling concepts later), regarding struggling with memory is something that happen here, in the forum, is about posting, sometimes ... I had ended not posting because of this disadvantage, but it is now (after reading such articles) that I had realized it.

I also read this one: Dyslexia and the Adult Learner _http://www.horne28.freeserve.co.uk/dyslex.htm

Are other languages easier for the dyslexic to read and write? Are languages with more phonetic or even non-alphabetic writing easier? Are there the same problems with Japanese kanji? Apparently not - Japanese writing uses 2 different systems pictograms (kanji) and phonetic (kana). The thousands of kanji cause fewer problems for dyslexics than the hundred or so kana (Thomson 1979 p41-2, Sasanuma 1980).

I can testify it, :) I study Japanese in my free time, it had been less and less others priorities as posting this had sent Japanese studies to … I had not been able to do it more constantly-, but I had observed that scars from dyslexia does not appear as much or does not appear, it is a way too different system of language. An one thing that I like it more in studying it, is the kanji.


I found this interesting also, differences in reading from dyslexics to non dyslexics: Brain Science and Dyslexia: How the Newest Studies Show why Dyslexics Must Use Unique Strategies for Reading, and How Davis Methods Build those Strategies _http://www.positivedyslexia.com/reading/article_brain_science.htm

This dyslexic difference can be explained by the model of picture-thinking vs. word-thinking. That is, the dyslexic thinks mostly with visual imagery, whereas the typical, non-dyslexic learner thinks mostly with the sounds of words. Brain scan research does also show that individuals tend to prefer either primary language-based problem solving approaches or visualization-based approaches; that these are reflected in different brain use patterns; and that individuals tend to reinforce their favoured modality through their thinking and learning processes, building stronger neural pathways and gaining proficiency.

There are other articles and new researches in development, but for this time, I thought it would be ok to post these, because I started reading other topics.

 

[casper]

An interesting article about dyslexia,
"What it's REALLY like to read with dyslexia: Simulator reveals how letters and words appear to people with the condition"
link:

http://www.dailymail.co.uk/sciencetech/article-3480257/What-s-REALLY-like-read-dyslexia-Simulator-reveals-letters-words-appear-people-condition.html

 

[Christine]

Je saisie l’occasion pour vous dire que je suis dyslexie, on ne m’a jamais diagnostiqué pour ce problème, ce sont mes enfants qui m’en on parlé en m’entendant déformer certain mots. Quand je parlais avec d’autres personnes je prenais un léger accent de mes parents (Mon père est Polonais, ma mère Allemande) pour dissimuler mon problème… J’ai aussi beaucoup de difficulté à formuler mes pensées surtout par écrit.
J’ai fait une recherche sur internet sur les signes révélateurs de la dyslexie, j’ai effectivement en moyenne aujourd’hui 60% des signes…il y a eu des améliorations avec le temps.

I seized the opportunity to tell you that I am dyslexia, I was never diagnosed the problem, they are my children told me they heard me some distort words. When I spoke with other people I took a slight accent of my parents (my father is Polish, my mother German) to hide my problem ... I also really difficult to formulate my thoughts especially in writing.
I did an internet search of the telltale signs of dyslexia, I actually mean today 60% of signs ... there have been improvements over time.

 

[Babylion]

i like this topic my mom was recently "diagnosed" with dyslexia and she often thought i had too. after reading more on this subject i believe i may actually agree with her. I'm guessing there are different degrees and types of dyslexia. so while i am trying to learn more about myself i found this very helpful in my journey of discovery. so thank you renaissance
never dismiss anyones views no matter if they are "stupid" we can always learn even from babies.
progression in life is understanding that the differences in each of us can also be seen as similarities
much love