MIT neuroscientists have found that the human brain can identify images seen for as little as 13 milliseconds.
This is the first evidence of such rapid processing speed of the brain – far faster than the 100 milliseconds suggested by previous studies.
Researchers at Massachusetts Institute of Technology (MIT) asked subjects to look for a particular type of image, such as ‘picnic’ or ‘smiling couple’, as they viewed a series of six or 12 images, each presented for between 13 and 80 milliseconds.
“The fact that you can do that at these high speeds indicates to us that what vision does is find concepts. That’s what the brain is doing all day long – trying to understand what we’re looking at,” said Mary Potter, an MIT professor of brain and cognitive sciences and senior author of the study.
This rapid-fire processing may help direct the eyes, which shift their gaze three times per second, to their next target, Potter said.
After visual input hits the retina, the information flows into the brain, where information such as shape, colour, and orientation is processed.
In previous studies, Potter has shown that the human brain can correctly identify images seen for as little as 100 milliseconds.
In the new study, she and her colleagues decided to gradually increase the speeds until they reached a point where subjects’ answers were no better than if they were guessing. All images were new to the viewers.
The researchers expected they might see a dramatic decline in performance around 50 milliseconds, because other studies have suggested that it takes at least 50 milliseconds for visual information to flow from the retina to the ‘top’ of the visual processing chain in the brain and then back down again for further processing by so-called ‘re-entrant loops’.
However, the MIT team found that although overall performance declined, subjects continued to perform better than chance as the researchers dropped the image exposure time from 80 milliseconds to 53 milliseconds, then 40 milliseconds, then 27, and finally 13 – the fastest possible rate with the computer monitor being used.
Potter believes one reason for the subjects’ better performance in this study may be that they were able to practice fast detection as the images were presented progressively faster, even though each image was unfamiliar.
The study also suggests that while the images are seen for only 13 milliseconds before the next image appears, part of the brain continues to process those images for longer than that, Potter said, because in some cases subjects weren’t asked whether a specified image was present until after they had seen the sequence.
The study was published in the journal Attention, Perception, and Psychophysics.
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