An illusion...

[kinyonga]

How many circles do you see?
http://www.whatispsychology.biz/the-coffer-illusion-explained

 

[Scottsquatch]

Less than ten seconds! I don't know why they just jumped out at me, but I'll take it!

 

[opheliaeatsbugs]

16 about 15 secs. I saw the four on the right quickly. Then squinted my eyes and saw the four on the left. the middle 8 took a second or two, eventho i knew they must be there.