A new study in Journal of Experimental Psychology: Human Perception and Performance has tested two possibilities – one is that after each blink your brain "backdates" the visual world by the duration of the blink (just as it does for saccadic eye movements, giving rise to the stopped clock illusion); the other is that it "fills in" the blanks created by blinks using a kind of perceptual memory of the visual scene. Neither explanation was supported by the findings, which means that the illusion of visual continuity that we experience through our blinks remains a mystery.
One experiment involved students making several judgments about how long a letter 'A' was presented on a computer screen (the actual durations were between 200ms to 1600ms; 1000ms equals 1 second). Sometimes the 'A' appeared at the beginning or end of a voluntary eye blink, other times it appeared during a period when the participant did not blink. If we backdate visual events that occur during blinks, then the 'A's that appeared at the beginning or end of a blink should have been backdated to the onset of the blink, giving the illusion that they'd been presented longer than they actually had, as compared with 'A's that appeared when there was no blink. In fact, the researchers found no evidence that the students overestimated the duration of 'A's that appeared during blinks.
|Figure one from Irwin and Robinson 2016|
We do know from past research that the brain to some extent shuts down visual processing during blinks – a study from the 80s shone a light up through people's mouths and found their ability to detect changes in its brightness was reduced during blinks, even though the blinks obviously didn't impede the light source. But what the new research shows is still unclear is how the brain weaves the loss of visual input during blinks into a seamless perceptual experience.
Summing up, the University of Illinois researchers David Irwin and Maria Robinson said the brain seems to ignore the perceptual consequences of blinks, but they're not sure how this is done. "Having ruled out the temporal antedating and perceptual maintenance hypotheses," they said, "the question still remains: Why does the visual world appear continuous across eye blinks?".
Irwin, D., & Robinson, M. (2016). Perceiving a Continuous Visual World Across Voluntary Eye Blinks. Journal of Experimental Psychology: Human Perception and Performance DOI: 10.1037/xhp0000267
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Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.
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