Saccades

2010/02/19 § 1 Comment

Saccades are quick, simultaneous movements of both eyes in the same direction.

In a writing a twitter story it may help to know how people read in terms of the biophysical mechanics of eye movement. One of the things people’s eyes do is to skip around while reading. This is because we can only take in so much in one chunk, and we like to jump ahead, or check back to what has gone before.

This picture shows the acuity of foveal vision in reading (during one eye stop). The lower line of text simulates the acuity of vision with the relative acuity percentages. To do a test close one eye, fixate the upper line at the fixation point and try to read the words to the right and left without moving your eyes. The result should be similar to the incrementally blurred lower line of text - except that you never have the impression of a blurred text. The reason: Your visual perception is already the result of a massive computational analysis made by your brain. Your system "knows" that the upper line is not blurred, so you don't see it as blurred. But the difficulty of recognition increases with the distance from the fixation point.

In terms of a twitter story’s elements it means that hiding things in pain sight is a bit difficult as people will tend to jump ahead of where they are reading, and a more predictable ending may well be saccaded over before they get there consciously. A non-cliched use of words will help here to maintain the surprise.

In terms of saccading back, readers will flick back to the beginning to check that they’ve ‘got it’. It will help readers reinterpret those first elements, and help them to build the story from the hints.

(If I look at the fixation point above I can actually see from ‘only’ to ‘five’ quite well. Does that mean my acuity is above average? Do people vary in acuity? Does this explain why some people find it harder to read?)

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