By Liz Seward
Science reporter, York
The mystery of how we read a sentence has been unlocked by scientists.
Reading is not as simple as scientists once thought
Previously, researchers thought that, when reading, both eyes focused on the same letter of a word. But a UK team has found this is not always the case.
In fact, almost 50% of the time, each of our eyes locks on to different letters simultaneously.
At the BA Festival of Science in York, the researchers also revealed that our brain can fuse two separate images to obtain a clear view of a page.
Sophisticated eye-tracking equipment allowed the team to pinpoint which letter a volunteer's eyes focused on, when reading 14-point font from one metre away.
Rather than the eyes moving smoothly over text, they make small jerky movements, focusing on a particular word for an instant and then moving along the sentence. Periods when the eyes are still are called fixations.
Professor Simon Liversedge, from the University of Southampton, said: "We found that in a very substantial number of fixations that people make when they read, they aren't looking at the same letter."
Instead, the eyes often focussed on different letters in the same word, about two characters apart, he said.
"They could be uncrossed, in the sense that the two lines of sight are not crossed when you look at a word, or alternatively the two lines of sight may be crossed," he added.
The team's results demonstrated that both eyes lock on to the same letter 53% of the time; for 39% of the time they see different letters with uncrossed eyes; and for 8% of the time the eyes are crossing to focus on different letters.
A follow-up experiment with the eye-tracking equipment showed that we only see one clear image when reading because our brain fuses the different images from our eyes together.
The tests showed that we use the information from both eyes, rather than our brain suppressing one image and only processing the other.
Professor Liversedge said: "A comprehensive understanding of the psychological processes underlying reading is vital if we are to develop better methods of teaching children to read and offer remedial treatments for those with reading disorders such as dyslexia."