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

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..."

Kindest Regards,

On 6/14/17, Laura Carlson <> wrote:
> Hi Wayne,
> Thank you!
> I updated the folks on GitHub:
> And asked Jim to put this on a future LVTF agenda.
> Kindest Regards,
> Laura
> On 6/13/17, Wayne Dick <> 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 Wednesday, 14 June 2017 13:54:11 UTC