The Spinning Girl Illusion Revisited
Three years ago I wrote a post about a popular illusion – the spinning girl or silhouette illusion. This is a popular online illusion, and also remains my most popular post. (Original illusion by Nobuyuki Kayahara here.) The popularity of this illusion seems to be tied to the fact that it is used in many online quizzes, with the claim that the direction in which you see the girl spin will tell you which side of your brain is dominant. In my prior post I primarily addressed that claim – explaining that the “left brain – right brain” thing is all nonsense, and which way the girl appears to spin tells you nothing about your personality or talents. (Briefly – while many neurological functions are lateralized to one side of the brain or the other, both hemispheres are massively connected and work together to form your abilities and personality.)
The real question prompted by this illusion is why do we perceive it as rotating one way or the other, and is there a preference. It turns out, most people will see the girl spinning clockwise. You can get her to switch and spin the opposite way to your original perception – but when first looking at the illusion most people will see her spinning clockwise.
Psychology professors Nikolaus F Troje and Matthew McAdam wrote a paper explaining this preference, and not surprisingly it has nothing to do with hemispheric dominance. It is purely a visual phenomenon – they write:
Here, we show that this rotational bias is in fact due to the visual system’s preference for viewpoints from above rather than from below.
Our visual system has many such biases and preferences. In effect, our brains process visual information with many default assumptions that are true most of the time. Many optical illusions are based upon creating a special situation in which one or more of these assumptions are false. For example, our visual system has a bias for lighting from above, assumes that smaller objects are farther away, and assumes that if one object overlaps another it must be relatively closer.
Troje and McAdam did some experiments with 24 subjects, playing with the apparent camera angle of the image. They found that there does not appear to be any rotational bias (preference for clockwise or counter-clockwise). The only bias they documented was the viewed from above (VFA) bias.
They also point out that silhouettes are inherently ambiguous – they do not provide clues for how to construct a 3-D image from the 2-D information. However, in this illusion there are subtle and conflicting clues for direction. They write:
Tracing the end of the outstretched hand shows that the camera elevation with respect to the hand is only 6.0 deg, which is a little less than the value for the foot. That means that the figure was rendered with a perspective camera positioned about 75 meters away from the figure (assuming a vertical distance of 1mbetween foot and hand). According to this perspective cue, the view from above and therefore the clockwise rotation is the ‘true’ rotation. However, another cue to the rotation of the figure is provided by the shadow the feet cast on the ground. The ellipse circumscribed by the shadow of the outstretched foot—at least assuming that the ground is horizontal and that we are looking at it from above—clearly suggests counter-clockwise rotation.
Their experiment and explanation is elegant, but it turns out the answer to this illusion was already available online. In addition to my post debunking the “left brain-right brain” claim, psychologist Michael Bach had also explained in 2007 the viewed from above bias as the true explanation. While I appreciate the extra detail and data provided by the new study, the answer was available online all along. (It should be noted that Troje and McAdam reference Bach in their paper.) Yet interestingly Bach's explanation did not get much attention, while this new paper is being credited as finally debunking the silhouette illusion as personality test.
It is good news that if you search on the various relevant search terms for the illusion, my blog post ranks highly (it is the first hit when you search on “the spinning girl”, and now the Troje and McAdam paper dominate the rankings as well. Hopefully this was all a good opportunity to teach the public a little bit about neuroscience and visual perception, and to make a dent in the popularity of the left brain-right brain myth that is so common.
This is also another episode that points out the frustrating disconnect between pop-psychology and actual psychology. So much of what passes for psychology in the public domain is nonsense, or is simply false or outdated information. Yet there are many interesting and useful psychological experiments out there that the public is not aware of. Psychologist Richard Wiseman discusses this briefly on the SGU, and says this was the motivation for his book, 59 Seconds, in which he debunks a lot of pop-psychology but then gives useful knowledge from the actual research.
I don't know if the internet and “web 2.0″ is helping or hurting this phenomenon. At least for those who are interested, the real information is usually available, and often long before it finds its way into the official literature. In this case it took three years to catch up – but better late than never.
Australians see it spinning counterclockwise.
Are you sure it’s due to the Coriolis effect, or is it just the way Aussies tilt their computer screens?
It’s because their visual systems prefer viewpoints from below rather than from above.
Nah, it’s just our penchant to be difficult and different to the rest of ya :-)
No, it’s because you drink too much beer and forget that your country is upside-down.
If you scroll down so you can only see the figure below the hips, the leg that’s in the air will appear to rotate toward you, and the figure will appear to spin back and forth.
Then, if you scroll up a bit, as soon as you see both arms, the figure will appear to spin clockwise.
75 meters? Maybe 7.5?
This is all virtual, so why not 75 meters? They could even make it infinity.
The image that appears on my screen appears to be a fully developed spinning woman. Why do you keep referencing a spinning girl? Aren’t you boys ever going to allow us to grow up?
To me it looks like a rendered silhouette of a computer model. In fact it looks an awful lot like a scene I created when I took an artist’s model and plonked it in a virtual world and forgot to calculate the lighting on the model. However, that particular model only jumped up and down and ran; it hadn’t been posed for a pirouette.
I use “girl” to describe any person of the female sex who is either 1: younger than I. 2: Who I am trying to flatter or 3: Who takes offense from me not using the word exactly according to the Oxford English Dictionary and I now just wish to annoy.
The definition of the word “girl” has evolved over the centuries. As one time it referred to a very young child of either gender. Then for a while is referred to a pre-adult female. In contemporary English it has come to mean either a young female, or a female of any age — depending on the context.
Your source is what?
I guess I’m not most people then. Nor do I have much control over which direction it appears to spin; it simply reverses now and then. Maybe it also has something to do with which frame I see first.
The clockwise motion was very persistent for me.I had to scroll down to where I could no longer see the shadow,and then stare at it for about 3 minutes.Gradually it began to go from clockwise to back and forth,then counter clockwise. Interestingly, when I couldn’t get the clockwise version out of my head,if I viewed it upside down,it also looked clockwise (which was counter clockwise in the normal orientation).
Change your viewpoint!
I can actually reverse the direction permanently by firstly viewing the girl from the top and then from below, by lowering my head or lifting the monitor.
To me, this illustrates, so to speak, something discussed in Goedel, Escher, Bach – on a fugue, do you follow an individual voice more, or the piece as a whole?
I’ve had that book for 30 years,and still haven’t read it :(
Looks good on my bookshelf though ;)
Am I the only one who thinks this has been animated with a bias? I mean, one motion of the foot has the foot significantly higher than the second motion of the foot (the shilouette descends a bit). That’s what creates a perspective and the illusion bias.
If the figure would not go up and down all the time, would we still perceive the spinning as predominantly clockwise? Does anyone know a better spinning animation?
I stared at the silhouette boobies for too long and got vertigo.
I always wonder what she looks like with the lights on.
To The Midwesterner:
Regarding your comment to Febo – “Your source is what?” – I happen to have researched the word “girl” once in the Oxford English Dictionary (OED) and fortunately saved the result on my computer. It included the following:
“1. Chiefly in pl. A child of either sex; a young person. Now Irish English (Wexford).
knave girl n. a boy.
c1300 St. Thomas Becket (Laud) 76 in C. Horstmann Early S.-Eng. Legendary (1887) 108 e Amirales dou ter was In e strete are-oute, And suy e gret prece of gurles and Men comen hire al-a-boute. c1400 (a1376) LANGLAND Piers Plowman (Trin. Cambr.) A. XI. 132 Gramer for girles [vrr. gurles, gerles, childeryn] I garte ferst write, And bet hem wi a baleis but if ei wolde lerne. c1400 (?a1300) King Alexander (Laud 622) 2798 Men mi tten seen ere hondes wrynge..Wymmen shrikyng, gyrles gradyng. c1405 (c1387-95) CHAUCER Canterbury Tales Prol. (Hengwrt) l. 664 In daunger hadde he at his owene gyse The yonge gerles of the diocise, And knew hir conseil, and was al hir reed. c1450 Bk. Curtasye 328 in Babees Bk. 308 Ne delf ou neuer nose thyrle With thombe ne fyngur, as ong gyrle. ?a1475 Ludus Coventriae 171 Here knaue gerlys I xal steke.
a1827 J. POOLE Gloss. in T. P. Dolan & D. Ó. Muirithe Dial. Forth & Bargy (1996) 49 Gurl, gurlès, a child, a girl. 1996 T. P. DOLAN & D. Ó. MUIRITHE Dial. Forth & Bargy 25 Gurl, a child of either sex.”
Obviously, I can’t know Febo’s source, but I would guess this would satisfy your curiosity.
Thanks for your interesting comment. Actually, I wasn’t particularly curious as I also have access to the OED (although haven’t done a lot of research ther) as well as other dictionaries. My point was that Febo didn’t offer an opinion but rather made a statement of fact and I was asking for the basis therefor. As to my original comment, I think Robo Sapien’s later comment supports my point.
What does it mean if I can only see it going counterclockwise??
That spinning girl is hot!
Which way is she really spinning, clockwise?
“You can get her to switch and spin the opposite way to your original perception – but when first looking at the illusion most people will see her spinning clockwise.”
That would depend on how the image was made.It appears that it is from a real life model that may have been standing on her left leg,in a stationary position,and not spinning at all.But,potentially, she would be going in the clockwise direction if she were standing on her left leg.However, she might have been on her right leg,which would mean that the apparent animated motion would be counter-clockwise.
The paper says, “According to this perspective cue, the view from above and therefore the clockwise rotation is the ‘true’ rotation.”
Because the image was rendered with a perspective camera, it shows some foreshortening, i.e. features further away are smaller, which tells you the direction the model is facing. Had it been rendered with an orthographic camera, there would be no such cue.
I could watch that for hours! Thanks!
I am dumbfounded that this would be perceived as spinning clockwise. I have stared at it and stared at it…and I can’t see how anyone could see this as spinning clockwise. Very interesting… I cannot visualize her spinning clockwise.