Line length revisited: after research

Mary Dyson produces filthy research on the long-accepted notion that shorter line lengths are more readable than longer ones. The study finds that shorter lines do not necessarily lead to faster reading. However, if you are looking for a definitive answer that you can use in your next design review debate, there are no dice. The big discovery is that long lines do not slow things down as much as previously thought, not that they are better or worse.

But there is so much more meat in here that I found much more interesting, mostly because I am largely unaware of the subject and got a bloated context about writing, readability, and behavior.

Things like…

There is an expression for transition between lines of text

It is return. You know what your eye hits Return key at the end of the line and swipe to the beginning of the next line. Then there is deficit. The idea is that the eyes may not go to the exact start of the next line, instead of stopping a little short.

These little quick eye movements between words and sentences? They are called saccader. I had to look it up.

The impact of deficits is what is being challenged

The previous research we have relied on for years dates back to 1940 (!), A time when we were obviously more preoccupied with paper pages than bright digital screens. Longer lines, it said, increased the likelihood of eyes underperforming during a recurring sweep, and undershooting results in a regression that results in a delay of 130 ms to 250 ms, which the brain needs to figure out. The report refers to it as undersweep fixation.

We can still process words during undersweep fixation

This report cites a 2019 study that attempted to correct deficits by marking the first word in bold at the beginning of each new line, a bit like an anchor that naturally draws the eye closer to the left margin.

The 2019 study found that words in bold reduced the number of recurring underruns, but despite that, reading speed did not improve. It is the driving force to challenge the long-held assumption that shorter is better.

Mary further explains:

In an attempt to reconcile why longer line lengths might not slow down the reading on the screen, but do so when reading print, I outlined some differences, e.g. visual angle, time spent scrolling. But while physical differences between screen reading and print reading still exist, we now have direct evidence to explain why longer lines were read at least as fast as shorter lines. Readers can process words during the short fixation as they underline the start of the new line. This saves time on subsequent treatment. Now we might also recognize that there is greater consistency between the range of optimal line lengths for print and screen.

Where does this leave us today?

Well, nowhere is closer to a clear answer we can use in our daily work. But it’s good to dust off our collection of best design and copywriting practices and know that line length is less of a limitation than it might have been.

Again, none of this tells us whether long or short lines are better. Mary concludes her report by saying that she can definitely not recommend using longer lines of text because there are clear texts because there are still some factors that come into play, including:

  • Shorter lines are more effective for people with dyslexia.
  • More questions about return sweep and undershooting need to be answered.
  • Several other studies suggest that users prefer shorter lines and rate longer lines as harder to read.

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