mardi 30 juin 2009

The Tom Cruise effect

I just found this picture from one of my favourite blogs, the Canadian Cynic (originally at the Photoshopping site
In the interest of cognitive science and skepticism, I just had to use it as a mini-primer on the Thatcher effect.
Look at it:

Well, that's creepy enough, isn't it? I mean, first of all, that's Tom Cruise, and as if that's not enough, he's upside-down but his face is not. Brrrrr. Something is definitely wrong with that picture, so wrong that I would have a very hard time locating it, even approximately, anywhere in the uncanny valley. Ok, but now look at what happens when that picture is further turned upside-down:

So, I ask you: which one is creepiest? Just look at them side by side, maybe this can help:

I would say the second one, on the right, looks even worse than the first one. If I had any readers on this blog, I would put on an online poll to settle the matter. But I'm all alone here, so I'll have to trust my own feelings.

Anyway, let's flesh out some background now. I think this is a rather extreme instance of the so-called Thatcher illusion ([1]; find the original, an hugely influential, paper by Peter Thompson here). This is very well known, but it's still an extremely efficient classroom demonstration of how the visual system deals with special objects like faces.

Look first at both pictures of Maggie in the lower row. The one on the left is normal, the one on the right is grotesquely deformes (eyes and mouth have been selectively inverted). In the upper-row, the images are simply inverted, and the striking discovery is that the "grotesque" Thatcher is much less grotesque in this orientation. The effect is generally interpreted as a demonstration of the fact that inverting a face disrupts configural processing, meaning that it's extremely hard to detect incongruencies in the location, size, distance, and overall relationships of isolated parts when the face is rotated 180°. There is actually some ongoing debate about the exact mecanisms involved in face processing and the real meaning of the Thatcher illusion, but I won't go into the details here.

Now, if you wonder what happens when the images slowly rotate or are rotated by 90°, you can test it yourself on Michael's Bach excellent website. If you want more theory of what's going on behind the Tatcher illusion, check this old post of the now-probably-defunct-but nevertheless-missed blog Mixing Memory.

Here's a variant of the Thatcher effect that I like very much, but which actual relevance to the effect discovered by Thompson can perhaps be questionned ([2]; it's a tribute to Thompson by Stuart Antis, which you can download here):

Again, see Mixing Memory for some explanation. But here's the caption by Anstis:
(a) Unretouched negative photograph of Tony Blair. This is analogous to an upside-down face. (b) Face is negative except for the eyes, teeth, and hair, which are positive. This is equivalent to an upside-down thatcherized face, but looks barely more grotesque than (a). (c) Reversing the contrast of (a) yields a normal photo. (d) Reversing the contrast of (b) yields a grotesque portrait, with the whole face positive except for the negative eyes, hair, and teeth. This is equivalent to an erect thatcherized face.
From the text, some sentences that deserve full re-transcription here:
I have done for negative faces what Thompson did for inverted faces. Figure 1a is a contrast-reversed portrait of Mrs Thatcher's latest successor, the much-loved Tony Blair, well-known for his gleaming eyes and teeth. Next to it is a modified negative (figure 1b), which looks similar to, or perhaps more lifelike than, 1a. In fact, the mouth, eyes, and hair in figure 1b were individually contrast-reversed before the whole picture was contrast-reversed, so these features are positive whilst the rest of the face is negative. This is analogous to thatcherizing the face in the contrast domain.
When these two pictures are viewed in positive, figure 1c is clearly normal, whereas the grotesqueness of figure 1d is vampirish enough to scare little Tory children.
And the glorious conclusion:
This would suggest that there are similarities between the Blair illusion and the Thatcher illusion (in much the same way as there are similarities between Blair and Thatcher).

So, how does all this relate to the Tom Cruise pictures? Well, I guess the Thatcher explanation will say that the head-inversion somehow disrupts the grotesque-ness of the face-inversion. As humans and their heads are overwhelmingly perceived in the upright orientation in daily life, and the visual system evolved to quickly make sense of facial identitites and expressions, then the manipulation in the second picture is even more obvious than the one in the first picture. Anyway, I can add another example so that you can make up your own mind, and then I'll leave it at that:

Which one is the creepiest?

[1] Thompson P, 1980, "Margaret Thatcher: a new illusion" Perception 9(4) 483 – 484
[2] Anstis, S.M. (2005). Homage to Pete Thompson: The Tony Blair illusion. Perception, 34, 1417

1 commentaire:

  1. wonderful information, I had come to know about your blog  from my friend nandu , hyderabad,i have read atleast 7 posts of yours by now, and let me tell you, your website gives the best and the most interesting information. This is just the kind of information that i had been looking for, i'm already your rss reader now and i would regularly watch out for the new posts, once again hats off to you! Thanks a ton once again, Regards, tom cruise workout plan