Volume 20, Issue 4, May 1997, Pages 147–152

Perspectives

To see but not to read; the magnocellular theory of dyslexia

• John Stein¹, 
• Vincent Walsh²

• ¹ Dept of Physiology, Parks Rd, University of Oxford, Oxford, UK OX1 3PT
• ² Dept of Psychology, South Parks Rd, University of Oxford, Oxford, UK OX1 3UD

• http://dx.doi.org/10.1016/S0166-2236(96)01005-3, How to Cite or Link Using DOI

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Developmental dyslexics often complain that small letters appear to blur and move around when they are trying to read. Anatomical, electrophysiological, psychophysical and brain-imaging studies have all contributed to elucidating the functional organization of these and other visual confusions. They emerge not from damage to a single visual relay but from abnormalities of the magnocellular component of the visual system, which is specialized for processing fast temporal information. The m-stream culminates in the posterior parietal cortex, which plays an important role in guiding visual attention. The evidence is consistent with an increasingly sophisticated account of dyslexia that does not single out either phonological, or visual or motor deficits. Rather, temporal processing in all three systems seems to be impaired. Dyslexics may be unable to process fast incoming sensory information adequately in any domain.

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Figures and tables from this article:

Fig. 1. Words can be hard to read for several different reasons. Visual confusions can cause letter reversals (‘worbs’), distortion and blurring (‘can be hard to read’) and superimposition (‘for several different’).

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Fig. 2. The magnocellular laminae of the lateral geniculate nucleus (mLGN) and visual deficits. The lateral geniculate nucleus (LGN) is a six-layered structure that receives input from the retinal ganglion cells and the primary visual cortex. There are important differences between the relative preferences of the four dorsal parvocellular (P) laminae and the two ventral magnocellular (M) laminae. Cells in the P, but not the M laminae, receive spatially segregated conederived inputs from small (P) retinal ganglion cells¹¹. M cells have larger receptive fields than P cells and a higher achromatic contrast sensitivity¹². From the point of view of dyslexia research, the most important differences between the two groups of cells are the faster conduction velocities and the high temporal (transient) sensitivity of the M cells compared with the sustained responses of the P neurones¹³. The laminar organization of the LGN can be exploited to demonstrate the functional significance of the differences between P and M cells. The figure shows the effect of LGN lesions on flicker (left) and motion (right) detection judgements in monkeys. When the parvocellular LGN was lesioned (A), the monkeys were unimpaired in the contralateral visual field (filled squares) on either task, compared with their performance in the spared ipsilateral (open circles) visual field. However, when a lesion was made in the magnocellular laminae (B), the monkeys were greatly impaired in flicker and motion judgements in the contralateral ‘magno-blind’ visual field. The opposite pattern of results was obtained when the monkeys were required to detect or discriminate colour, form, size, texture or disparity¹⁴. The specificity of these findings is mirrored in the specificity of visual deficits reported in dyslexia. Data replotted from Ref. 14.

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Fig. 3. Functions of the posterior parietal cortex (PPC) and their relations to dyslexia. The different shading patterns show the separate subareas of the PPC. Damage to each region can produce specific deficits: spatial mislocalization may be associated with damage to areas 5 and 7; spatial disorientation with damage to areas 5, 7 and 39; neglect with damage to areas 39 and 40; ‘cocktail party’ problems with damage to area 40; visuomotor co-ordination with damage to areas 5, 7 and 39; and visuoverbal association with damage to area 40.

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Fig. 4. Left neglect in a dyslexic child. The child's age was 7 years 11 months, with a reading age that was retarded by 20 months. The child's I.Q. was 92.

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The neurological basis of developmental dyslexia

http://brain.oxfordjournals.org/content/123/12/2373.short

Dr Michel Habib, Centre de recherche, Institut Universitaire de Gériatrie, 4565 Ch. Queen Mary, Montréal (QUE), Canada H3W 1W5 E-mail: rnp@romarin.univ-aix.fr

• Received January 24, 2000.
• Revision received June 20, 2000.
• Revision received July 25, 2000.
• Accepted July 27, 2000.

The neurological basis of developmental dyslexia

An overview and working hypothesis

Five to ten per cent of school-age children fail to learn to read in spite of normal intelligence, adequate environment and educational opportunities. Thus defined, developmental dyslexia (hereafter referred to as dyslexia) is usually considered of constitutional origin, but its actual mechanisms are still mysterious and currently remain the subject of intense research endeavour in various neuroscientific areas and along several theoretical frameworks. This article reviews evidence accumulated to date that favours a dysfunction of neural systems known to participate in the normal acquisition and achievement of reading and other related cognitive functions. Historically, the first arguments for a neurological basis of dyslexia came from neuropathological studies of brains from dyslexic individuals. These early studies, although open to criticism, for the first time drew attention towards a possible abnormality in specific stages of prenatal maturation of the cerebral cortex and suggested a role of atypical development of brain asymmetries. This has prompted a large amount of subsequent work using in vivo imaging methods in the same vein. These latter studies, however, have yielded less clear-cut results than expected, but have globally confirmed some subtle differences in brain anatomy whose exact significance is still under investigation. Neuropsychological studies have provided considerable evidence that the main mechanism leading to these children's learning difficulties is phonological in nature, namely a basic defect in segmenting and manipulating the phoneme constituents of speech. A case has also been made for impairment in brain visual mechanisms of reading as a possible contributing factor. This approach has led to an important conceptual advance with the suggestion of a specific involvement of one subsystem of vision pathways (the so-called magnosystem hypothesis). Both phonological and visual hypotheses have received valuable contribution from modern functional imaging techniques. Results of recent PET and functional MRI studies are reported here in some detail. Finally, one attractive interpretation of available evidence points to dyslexia as a multi-system deficit possibly based on a fundamental incapacity of the brain in performing tasks requiring processing of brief stimuli in rapid temporal succession. It is proposed that this so-called `temporal processing impairment' theory of dyslexia could also account for at least some of the perceptual, motor and cognitive symptoms very often associated with the learning disorder, a coincidence that has remained unexplained so far.

link to causes dyslexia website

http://archive.excellencegateway.org.uk/page.aspx?o=126809

A Brief Historical Overview of Typography Trends

http://inspiredm.com/typography-history/

A Brief Historical Overview of Typography

Trends

Typography has existed for thousands of years in various forms. Before we dive into the historical progression of this art, however, let’s start out with a solid definition.

What is Typography?

Typography is simply the art of letters and arranging type. That is, the evolution of type faces over time and how handwriting transformed into printed type.

Aside from the typeface, the other vital facets that make up the art of typography are known as point size, line length and leading. Further aspects to take into consideration are tracking (space between groups of letters, or words) and kerning (the space between individual letters).

Beginnings of Typography

Credit: oldmantravels

Around 5000 years ago, prior to the printed letters we typically think of that constitute typography today; the ancient Chinese, Sumerian, and Egyptian civilizations were communicating with each other using pictographs; a simplified set of images used to communicate messages to one another. This progressed into ideographs, which used more abstract versions of pictures and symbols respectively to describe objects and happenings. Eventually this progressed to hieroglyphics, which were developed by the Ancient Egyptians and utilized drawings to represent objects, events and even sounds.

Phoenicians to the Romans

The Phoenician alphabet was the first to include letters alone and was developed around 1200 BC The Greeks took this and added vowels. Finally, the Romans created their own alphabet with 23 letters that was a derivation from both Etruscan and Greek languages. Romans also added serifs, or strokes at the ends of letters. By the year 1500, the letters U, V and W were added as were punctuation marks.

The Role of Printing

Credit: NYC Wanderer

The very first system for allowing moveable type was developed in ancient China around 1040 AD by Bi Sheng, who crafted the clay method of printing. Barely any records of Sheng’s life exist, but what is known about him; aside from creating moveable type, is that he had no official stature or occupation. Moveable clay type soon evolved into the wooden form, allowing for printing to be done on a larger scale.

In the 1400′s, Johannes Gutenberg crafted the moveable type using lead, tin and antimony components, making it possible for materials to be printed in mass quantities. Using this revolutionary method, Gutenberg created the signature Gutenberg Bible in 1456. It was the first ever book to be printed and the finished product established the metallic method of moveable type as the definitive form of printing from then on. In fact, it is widely considered to be the most important invention of the second millennium.

The History of Typefaces

Several typefaces or fonts have been prevalent in modern history. Claude Garamond created the Garamond typeface, which was the first font to have the characteristic blocky look we associate with text today, rather than all previous typefaces that looked like handwriting.

John Baskerville was next, creating a Roman-esque typeface that included both thin and thick strokes with incredibly sharp serifs. And then Firmin Didot and Giambattista Bodoni came up with the Modern Romans in 1780, which use vertical stresses and super thin strokes. William Caslon IV created the very first sans serif typeface in 1816 and received harsh criticism for it.

By the time we get into the 20th century, however, there are numerous kinds of typefaces, many of which were developed by Frederic Goudy, who worked on the task full time making fonts like Broadway and Goudy Stout.

Modern Typefaces and Fonts

Credit: ibaldwindesign

One of the most popular typefaces of modern times is Helvetica, which was created by Max Miedinger in 1954. Once computers came into existence, typefaces and fonts expanded even more. Adobe created Postscript to describe fonts with math rather than pixels. The first fonts to be included on the Laserwriter included Helvetica, Courier, Times and Symbol. Each iteration of Laserwriter after that included more and more font selections. Type 1 postscript fonts are still the favored font types today because they are professionally designed and clean in format. Truetype is another kind of font technology, but it is not as reliable and often rejected by printers.

Now that the digital age offers the art of typography on the Internet, the scope for experimentation has never been wider. However, not every web browser is equipped to view every font. That’s why web designers are required to select web safe fonts like Times New Roman, Arial, and Courier New when developed text for the web. Otherwise, it could appear pixelated, blurry or, even worse, display unwanted coding.

It wasn’t until the Netscape browser was introduced in 1995 that diversifying fonts became a possibility. This was all thanks to the tag, which became standardized with the arrival of HTML 2. As web standards progress, the ability to utilize various, and customized, web fonts is becoming ever more of a probability; especially now that cascading style sheets (CSS) are common practice amongst web designers, developers and even those less savvy in style sheet language.

It could be argued that today’s typography trends tend to favour sans serif styles, due to its modern aesthetic. In web design, especially, sans serif fonts are used over serif in order to avoid the messy pixilation that is typical with many serif styles. While serif will never completely die out, its popularity has be considered as the progression and usage of digital technology evolves over time.