Re: A BRIEF ENCAPSULATION OF USER VISUAL NEEDS

Hi Jim,

This information is out of date. The report may have been published
recently, but the background research is old.

The critical print size is about 2 times to 2 and 1/2 times the acuity
limit. [legge, Bigelow, "Does Print Size Matter"]. This is true for normal
and low vision. This means that 20/50 requires about 250% enlargement. 2/60
requires 300% etc. for critical print size. If the person has central
retina damage the magnification factor is greater.

Here is the math. The normal acuity limit at 16 in. is around 4.5pt with
really clean eye chart font. Double that an you get 9pt, newspaper size.
2.5 of that is is 11-12pt rounding. Now if you have 20/40 vision your
critical print size at 16 in. is 9pt.  Double is 18pt and 2.5 times is
22pt. at 16in. Of course 20/160 requires 8 times that. That is hard to do
even digitally, but 4 times at 1/2 distance is effectively 800%.

The critical print size is the minimum size a person can read at optimum
speed and error rate.  The sizes suggested in WHO report will definitely
result in size induced slow reading and a serious error rate. These numbers
look like the kind of pre-digital data that was used for 1.4.4. We need to
stop that old data. When print was on paper, 200% was all anyone could
achieve. A pamphlet enlarged to 400% would become a small encyclopedia. We
can do lots better today with digital data in markup language.

Best, Wayne

On Thu, Sep 19, 2019 at 12:51 PM Jim Allan <jimallan@tsbvi.edu> wrote:

> This comes from the AG (WCAG) list. Passing along for consideration.
>
> ---------- Forwarded message ---------
> From: Andrew Somers <notifications@github.com>
> Date: Tue, Sep 17, 2019 at 9:08 PM
> Subject: Re: [w3c/wcag] Proposal for color and contrast (1.3.1, 1.4.1,
> 1.4.3., 1.4.6, 1.4.11) (WCAG 3.0) (#901)
> To: w3c/wcag <wcag@noreply.github.com>
> Cc: Subscribed <subscribed@noreply.github.com>
>
> <snip>
> A BRIEF ENCAPSULATION OF USER VISUAL NEEDS: *Visual Acuity deficits:*
>
> Acuity is essentially the ability to resolve a stimuli in the eye and
> perceive it in focus. “Blurryness” is the plain language way to describe
> poor acuity.
>
>    - A _primary_way to assist visual acuity is corrective refraction
>    (glasses/contacts) which is outside scope. In terms of display or design,
>    and for all other things being equal, acuity is assisted by the
>    appropriate _SIZE_which needs to be within a range (not too small but also
>    not too big) for best perception.
>    - Some causes of acuity loss, such as cataracts, require surgery to
>    correct.
>    - Classification of Acuity can be divided into three broad groups:
>       - *20/10 thru 20/63:* normal through near-normal. Existing
>       standards tend to be built around this range, which relates to a font size
>       of 12pt on the printed page. This serves as a “baseline” or foundation from
>       which stronger accessibility needs can be defined. 20/30 is the lowest
>       acuity for a private pilot, and 20/40 is the lowest for non-commercial
>       drivers in most states.
>       - *20/70 thru 20/200:* Low Vision, per the WHO definition. If a
>       font at 100% size is good for 20/63, then if you double the size to 200%
>       (24pt), you accomodate 20/150. To accomodate 20/200, then increase size to
>       275% (33pt).
>       - *Above 20/200:* Legally blind. 20/400 needs 550% larger size
>       (66pt).
>    - *Discuss* size adjust (user) and design minimums. And accommodating
>    user changes without breaking content, etc. (methods).
>
> *Contrast Sensitivity deficits:*
>
> Contrast Sensitivity Function (CSF) can be impacted by poor acuity, by
> retinal disease such as AMD, retinal migrains, by degraded ocular media
> (cataract, etc), and by neurological problems (MS, neuropathy). *VERY
> ROUGH (to be written):*
>
>    - CSF deficits caused due to poor acuity (blurry vision) is typically
>    helped best by addressing the acuity issues when possible.
>    - CSF is directly linked to spatial frequency (i.e. size), especially
>    closer to threshold.
>    - Increasing stimulus size will increase perceived contrast (within a
>    range).
>    - A key aspect of stimulus size is the stroke width of a font (i.e.
>    font “weight”) — Increasing a font’s size increases perceived contrast, but
>    largely due to the increase of stroke width as rendered to the screen.
>    Stroke width is the aspect of a font that most closely follows Michelson
>    Contrast (gratings).
>    - Aging ocular media (lens, cornea, vitreous) can affect contrast, but
>    moreover these can cause problems with glare which reduces perceived
>    contrast, while simultaneously being made worse as stimulus contrast
>    increases.
>       - Intraocular glare reduces or obscures perceived contrast, but
>       contrast perception is improved by _reducing the contrast _of what is being
>       viewed.
>       - Put another way, higher contrast objects cause more glare which
>       reduces the “contrast legibility” versus lower contrast objects that cause
>       less glare. The extreme example is headlights from an oncoming car at night.
>    - *TBD Discuss: luminance contrast, threshold vs supra and critical
>    contrast levels. Discuss design contrast. Discuss display luminance adjust
>    (user). Discuss polarity.*
>    - Contrast Sensitivity Function is typically measured with a
>    Pelli-Robson style of chart, which measures the “just noticeable
>    difference” or threshold of visibility.
>       - A Pelli-Robson score of 2 indicates “perfect normal vision
>       contrast” which equates to a contrast of 1% (i.e. 1.01 to 1 )
>       - A score of 1.5 is a noticeable degrading of CSF, and equates to a
>       contrast of 3% (i.e. 1.03 to 1)
>       - A score of 1 is a serious contrast impairment, and equates to a
>       threshold contrast of 10% (1.1 to 1)
>       - These are a measure of the point where a stimuli becomes visible,
>       which is useful in a clinical setting for detecting disease, but do not
>       indicate the level of “critical contrast” where an item is “most readable.”
>
> *Visual Field deficits:*
>
> Closely related/essentially part of contrast sensitivity impairments are
> those relating to visual field.
>
>    - Central vision loss is a loss of vision in the fovea (central
>    vision) forcing these users to learn to read using their peripheral vision.
>    - Peripheral blindness, or narrowing of the visual field (aka tunnel
>    vision),
>       - Makes it harder to notice changes in content (i.e. a warning
>       message) outside of the area the user is looking directly at.
>
> *Color Vision deficits:*
>
> Color Vision Deficiency (protan, deutan, tritan CVD types) is primarily
> helped by ensuring there is enough luminance contrast between items (i.e.
> between text and a background, or between roadways on a map and geographic
> features on the map).
>
>    - Also, ensure that color is not used as the sole means of providing
>    information (that is, don’t rely on “red” as a color that means “stop” —
>    descriptive text of symbols are also needed to communicate meaning.)
>    - Protanopia (red deficient) may have problems with some monitor types
>    (such as UHD/Rec2020) the red primary is close to the cut off for the green
>    cone and is perceived much darker.. *(need plain language for this)*
>    - sRGB monitors are recommended for Protanopia as the red primary is
>    within the green cone sensitivity. The protan will see this red a little
>    darker, which should be considered in calculating contrast.
>    - The rare monochromats are also aided by luminance contrast, though
>    may need to set the display to a monochrome mode, and have control over
>    luminance and ambient illumination (such as for rod monochromacy).
>
> *Cognitive/Neurological related Visual Deficits:*
>
> 62% of the brain is involved in visual processing. Over 20% of the brain
> is dedicated to visual processing, and of 42% processes visual in
> conjunction with other senses such as auditory and tactile.
>
>    - The other impairment types above are mostly associated with the eye
>    itself, these are associated with processing the signals from the eye.
>    - Someone who had a stroke, and the stroke damaged some part of vision
>    processing may have a problem with only that aspect of vision. For
>    instance, if the motion detection part of the brain is damaged, they may
>    see a car that is parked, but when the car moves it “disappears” in that
>    the brain ignores it/it is nor “perceived” (“ *visual neglect* ”)
>    - With *agnosia,* the visual pathways and brain are capable
>    of _seeing_objects or people, but cannot _recognize_them.
>    - Cognitive impairments, brain damage (from stroke or other incident)
>    can also cause some of the functional problems normally associated with
>    ocular impairments, such as  blurred vision, field loss, light sensitivity,
>    hallucinations, etc.
>    - Ocular migraines can directly interfere with vision by introducing
>    “blockage” to vision, such as with ocular migraines auras, which can appear
>    as zig zags in the vision, “seeing stars”, etc.
>
> In Closing
>
> Some of things you mention in your initial issue are fairly well
> understood, and in fact making their way into either SC extensions for 2.2,
> or new standards and guidelines for Silver. (One example is font weight, as
> those proposed SCs are already being created).
>
> However, you make statements that are not supported by research, your
> codepen notwithstanding. Visual perception is not binary logic, so
> "absolute" statements don't really fly in a field where there *are no
> absolutes.* Human perception is far more complex than can be determined
> by some examples at maximum contrast.
>
> I have listed references and footnotes to authoritative research
> supporting most of my posts in #695
> <https://github.com/w3c/wcag/issues/695> and elsewhere, and I do suggest
> reading through those references to gain a better understanding of the
> underlying concepts. In particular you might want to read Legge's book
> Psychophysics of Vision.
>
> And please keep in mind these standards are ultimately about the
> functional needs of a very wide swath of users & impairments. It is needs
> that should be considered, not so much the abstraction layer methods.
>
> Regards,
>
> Andy
>
> Andrew Somers
> WAI Invited Expert
>
>
> *Color Science Research Silver Task Force Low Vision Task Force*
>
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> --
> Jim Allan, Accessibility Coordinator
> Texas School for the Blind and Visually Impaired
> 1100 W. 45th St., Austin, Texas 78756
> voice 512.206.9315    fax: 512.206.9452 http://www.tsbvi.edu/
> "We shape our tools and thereafter our tools shape us." McLuhan, 1964
>