Take a look at this slideshow (QuickTime required). You’ll first see a photo in perfect focus. Then 12 more pictures will flash by, each of them blurred using Photoshop. Finally, the original photo will appear again. Is it the same as before, or slightly blurrier or sharper?
I’ll give the answer after a few readers have had a chance to make a guess in the comments. Most people with normal vision will gradually adapt to blurry photos (though it might take a little longer than I’ve allowed in this movie). Then when they see a photo that’s in focus, it seems too sharp — as if it’s been artificially sharpened like this picture:
Photos that are slightly out of focus (though not as blurry as the set of blurry photos they adapted to) will seem just right. But what about older individuals, whose eyes are less sensitive to contrast and brightness, and whose visual systems in the brain may also have degraded?
A team led by Sarah Elliott showed sequences similar to the movie above to 10 young adults (average age 25) and 10 older adults (average age 74). Their sequences were much longer (about 2 minutes), and several tests were administered, with blurred, neutral, and sharpened images. At the end of the sequence, the viewers were asked if the properly focused image seemed too blurry or too sharp.
As expected, most viewers who had seen blurry photos throughout the process thought the final image was too sharp. They were shown the blurry photos again, then viewed the test image again — but this time the image had been very slightly blurred (2 percent of the fully blurred amount). Again, viewers were asked if it was too blurry or to sharp. This was repeated until the viewers said the image was too blurry. Then the test image was sharpened again until viewers reversed their opinion. After several reversals, the researchers could determine the point at which a given viewer was neutral — where the image seemed neither too blurry or too sharp. Here are the results:
The older adults accepted significantly blurrier images than younger adults. Even when they were originally shown focused photos, their responses were neutral to slightly blurred photos. But this was a systematic bias: it occurred at every level of blurriness/sharpness of the original photos during the adaptation phase. While younger adults accepted blurry images after adapting to blurry images, older adults accepted even blurrier ones. Once the researchers adjusted for this systematic bias, the results for younger and older adults were the same.
So overall, it seems, even as the visual system deteriorates with age, we are able to adapt to these changes remarkably well. From the perspective of the individual, while everything fades a little bit, the differences between the items we perceive remain constant.
Were you able to detect any changes in the “in focus” photo from the movie at the beginning of this post? Let us know in the comments.
Elliott, S.L., Hardy, J.L., Webster, M.A., & Werner, J.S., (2007). Aging and blur adaptation. Journal of Vision, 7(6), 1-9. DOI: 10.1167/7.6.8