Re: Letter and Word Spacing: Final Analysis

```Hi Wayne,

Thank you!

I updated the folks on GitHub:
https://github.com/w3c/wcag21/issues/78#issuecomment-308421776

And asked Jim to put this on a future LVTF agenda.

Kindest Regards,
Laura

On 6/13/17, Wayne Dick <wayneedick@gmail.com> wrote:
>  *Letter and Word Spacing* *Summary of Results:*
>
> For best reading results the spacing should be .25em maximum. However, the
> loss of performance between .12em and .25em is less than 1/4 in reading
> speed. I think .15em is the best because that gives 95% of the benefit.
> After that there is almost no benefit. After .25em there is none.
>
> Word spacing may not be necessary, because browsers tack on the letter
> spacing to the normal word spacing anyway.
> *Good News / Bad News*
>
> The good news. Alastair and I are both right in our calculations.
>
> The bad news. Alastair and I are both right in our calculations.
>
> We have a serious political decision to make.
> *Analysis*
>
> My letter spacing was based on an article, “A study of the effect of letter
> spacing on the reading speed of young readers with low vision”, Eve
> McLeish, Visual Impairment Service, UK (British Journal of Visual
> Impairment 25(2) 2007). In this article, the author builds a table for
> spacing of typed assignments for children with low vision. The formula she
> used was STEP=[fontSize/20], for each test bracket. Each STEP represents
> increasing the letter spacing by 1/10 of the letter size. She used points
> for her font size but we will use pixels.  McLeish found significant
> results with reading speed up to n*STEP for n=1… 5. However, the slope went
> from steep to horizontal in this range. It was concave down going flat at
> n=5. When I computed these results, I started at n=5. Example: for font
> size of 16px, 5*STEP = 5(16px/20)=4px=0.25em. The formula works the same
> for all font sizes.
>
>
>
> I got to these values the first time and noticed that the performance curve
> really flattened between n=3 and 5. It grew from 0 to 20% increase in
> reading speed from n=0… 3. Then grew from 20% to 22% between 3 and 5. I
> should have selected 3 first and got 3*.8=2.4px= .15em.  Fear of developer
> response, got the best of me, so I suggested the .12em. At that size, the
> performance curve still gave a 15% increase in reading speed.
>
> For testing, I used Firefox with, Tahoma and the text, “Lorem ipsum dolor
> sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut
> labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud
> exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis
> aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu
> fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt
> in culpa qui officia deserunt mollit anim id est laborum.” I got the
> following results:
>
> Let Average Char be the number of pixels taken by an average character in
> the passage.
>
> Letter Spacing
>
> Average Char
>
> Increase
>
> Normal
>
> 7.004px
>
> 0
>
> 0.12em
>
> 8.921px
>
> 1.917px or 27%
>
> 0.15em
>
> 9.404px
>
> 2.4px or 34%
>
> 0.25em
>
> 11.004px
>
> 4.0px or 57%
> *Controversy*
>
> Aside from the huge impact on layout there are other difficulties.
>
> The research is mixed. The benefits of letter spacing are measured by
> various experiments in the range from no effect to simply miraculous.
> McLeish is in the middle; her methodology is sound, and she observes the
> impact in the most natural setting. Her findings rang true with my
> experience.
>
> The most significant article that shows no effect is: The effect of letter
> spacing on reading speed in central and peripheral vision by S. T. Chung
> (Investigative Ophthalmology and Visual Science, 2002 Apr, 43(4):1270-6).
> Chung’s methodology is sound, but she uses a different instrument for
> measurement. McLeish uses flash cards while, Chung uses Rapid Serial Visual
> Presentation (RSVP). The words are drifted past at varying speeds. Chung’s
> theory is that an individual can read faster when more letters are fit in
> the most sensitive reading zone of a reader’s retina. Increased letter
> spacing reduces this value and therefore reading speed must suffer.
>
> Both authors are correct, in my opinion.  This needs to be tested of
> course, but here is my reasoning. McLeish’s use of cards, forces the
> participant to orient their most sensitive reading zone each time the card
> is presented. Thus, McLeish measures orientation and recognition. Chung
> uses text that drifts into the participants optimal reading zone, so no
> orientation is needed. This would mean that the benefit in letter spacing
> would be in helping the reader orient their most sensitive reading zone to
> the target.  That is just a theory, but it does explain the difference in
> two well designed studies.
>

--
Laura L. Carlson
```

Received on Wednesday, 14 June 2017 13:30:09 UTC