Impossible Arch Puzzle

I found this image in my optical illusions folder today, and wondered why I never got the time to publish it. Look at the picture on your left. What do you see? There must be something strange going on here. No way that the arch shown here has the proper top. Or can it? I’ve also included a solution inside this post. You’ll have to click the expandable box to see it. I wouldn’t want to ruin your solving experience before you’re ready to see the answer. Anyway, by looking at the solution everything becomes clear. Why has our brain presumed the column is aligned differently than it actually is? I really can’t tell, but hope some of you will try and explain this through comments.

Yesterday I tipped you about new Facebook vanity URLs. Have you had the time to check them? Hope you managed to grab something short and unique to represent you, like I did. But it seems not many of you actually read what I post. Probably you check only the illusions, which is also fine. But I’m REALLY curious what names were taken by our audience. Would be very nice to see more and more of you using your facebook logins to post comments. Not only does this automatically shows your image next to your comment, but additionally you have an option to share your comment so it appears in your Facebook feed. This way you can help us reach more people (your friends will see that you left a comment on our site, if you approve it). What is your opinion on this?

Click To Expand the Solution