It has sometimes been assumed that we experience brief periods without vision every time we shift our focus from one point to another – but it turns out this is wrong.
Several times each second, we quickly change our line of sight, shifting our focus from one point in a scene to another. These fast, jerky eye movements, or saccades, each last less than 50 milliseconds, and our vision is reduced during that time. Some people have argued that our eyes lose their ability to process visual information in this time.
Richard Schweitzer and Martin Rolfs at Humboldt University of Berlin in Germany have shown that this isn’t the case: we are, in fact, able to absorb information from our surroundings during such rapid eye movements.
“This kind of changes the way we approach perception because we used to think about motor actions and perception as two distinct things,” says Rolfs. “What this insight shows, I think, is that as we continue to interact between how we move and what we perceive, that it’s not two separate processes. It’s two things working together; they go hand in hand.”
The pair worked with 20 volunteers who were asked to seek out and focus on a visual target displayed on a screen, which naturally encouraged their eyes to dart around performing saccades. However, the target on the screen was shown using a high-speed projector that was capable of generating about 70 images during each 50-millisecond-long saccade. This meant the researchers could have the target move smoothly so that its position at the end of the saccade was different from its position at the start.
The volunteers detected this within-saccade movement: at the end of the saccade, when their eyes looked for the target again, they seemed to have anticipated where the target would now be located. The researchers could confirm this because the volunteers were able to correct their eye movement to locate the target more quickly than would have been the case had their eyes not detected the target’s movement during the saccade.
“The paper suggests that during eye movements, what is left of motion streaks (the traces left in our visual system by fast-moving objects) helps perception, whereas it is a disturbance when the eyes are steady,” says Paola Binda at the University of Pisa in Italy. “This point would need direct testing, of course, but it is an intriguing one.”
“The only potential criticism I can see is that the results were obtained with stimuli ingeniously designed to investigate these effects, but it is not clear whether any of this occurs in natural vision – as the authors admit,” says Karl Gegenfurtner at Justus Liebig University Giessen in Germany.
Journal reference: Science Advances, DOI: 10.1126/sciadv.abf2218
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