RE: Letter and Word Spacing: Final Analysis

All,

I reviewed the McLeish study as well and I think I concur mostly with Wayne.  It's worth noting though there is large scatter in the data though, especially above 0.15em ("normal + 30%" in the article).  The trend line shown is not described, but appears to be a simple least-squares fit.  Given the scatter, the choice of curve fit would also affect interpretation.  Based on this study, I think we need to cap any SC number to less than 0.15em, so I'm fine with the original 0.12em.

I also would subscribe to Wayne's theory about RSVP being a very unrealistic approach to measuring reading speed for folks with low vision.  There's no way it's a Galilean invariant process.

One thing I'd disagree with though is about word spacing.  We either need to find a study on this or apply a proportionality rule or some other logic.  As letter spacing goes up, the ratio of space between words to space between letters goes way down, so eventually it'll just look like a string of letters.  Do we have any articles that studied them together?  If not, I'd set word spacing so that ratio remains roughly the same.

I do need to go back and fix my equations though because I had assumed letter spacing was not added between words.

Steve

-----Original Message-----
From: Laura Carlson [mailto:laura.lee.carlson@gmail.com] 
Sent: Wednesday, June 14, 2017 9:54 AM
To: Wayne Dick <wayneedick@gmail.com>
Cc: public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
Subject: Re: Letter and Word Spacing: Final Analysis

Hi Wayne,

In case you missed this study when Mike Gower posted it on GitHub:

Extra-large letter spacing improves reading in dyslexia http://www.pnas.org/content/109/28/11455.full


A while back I found Legge's Aug 2016 study, "Reading Digital with Low Vision". He says: "Overall, the evidence indicates that increasing spacing between letters is not helpful..."
http://search.proquest.com/docview/1825176282


Kindest Regards,
Laura

On 6/14/17, Laura Carlson <laura.lee.carlson@gmail.com> wrote:
> 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
>


--
Laura L. Carlson

Received on Friday, 16 June 2017 17:55:09 UTC