designmango-The Elusive Bistable Ballerina

The Elusive Bistable Ballerina

To you, does this silhouette of a woman appear to be spinning clockwise or anti-clockwise? 

Also known as the Silhouette Illusion, it was originally released in 2003 as a GIF animation of a pirouetting female dancer. The optical illusion was created by Japanese web designer Nobuyuki Kayahara, and it works by using motion to stimulate your brain. 

Majority see her spinning clockwise while others claim she's spinning anti-clockwise. Interestingly, some people may also see the dancer spin one way and then suddenly spin in the opposite direction as well. 

The Spinning Ballerina.(Center) The Clockwise Spin (Left), and the Anti-Clockwise Spin(Right).

One popular theory that seeks to explain the phenomena states that the direction of the movement  has to do with which side of your brain is more dominant. If your right brain dominates, you see her spin clockwise; if your left brain dominates, then you see her move counterclockwise. 

Another theory states that the reason we see her spinning in different directions is actually much more complex than which side of our brain dominates. 

It's important to understand that the spinning ballerina falls under a class of optical illusions called ‘reversible images’. What’s that you might wonder? Imagine a picture of a duck. Now, let's say, if you turn the picture upside down, suddenly it looks like a rabbit. That's what reversible images are all about- pictures that can be seen in more than one way, depending on how you look at them. 

Further, even though she spins, she bears similarities to other static illusions, like Necker cubes. Necker cubes are like 3D optical illusions on paper. They're simple drawings of cubes, but your brain can't decide which way the cube is facing. Sometimes it looks like the cube is coming out towards you, and other times it seems like it's going away from you. It's a fun trick that shows how your brain interprets 2D images as 3D objects. 

Reversible images like this puzzles us because they're ambiguous. They don't provide enough depth clues to make definitive sense. Your brain doesn't like when images don't make sense, so it imposes meaning where there isn't any. In other words, your brain’s taking a guess at what the possibility of the situation could be. 

This ambiguity leads to something called ‘bistable perception’ which means multiple perception, leading to the different directional outcomes. 

One way to ‘cheat’ the illusion is to add some sort of data or depth to it. For instance, if this spinning dancer’s silhouette had contour lines on her body or was wearing bright colored Lululemon pants, it'd be easier for your brain to decode what she's upto. But that takes away the illusion’s fun. Arthur Shapiro, a computer science professor at American University has an alternative solution that don't require cheating, just the right use of your brain. He says, “Imagine you are physically moving up or down in space. If you want her to switch directions, look at her as if you're filming her from below. Now pretend to be filming her from above”, and apparently in doing so, the spinning girl moves counterclockwise if one imagines themself below her, and clockwise if imagined to be above her.

In real sense, the spinning dancer doesn’t offer any precise measure of a person’s brain-part dominance. It is only a visual preference sign of the viewer. According to scientific studies, our vision bears numerous preferences. The majority decision to look at the dancer as whirling clockwise is influenced by the preference to observe things from above and not below. Researchers argue that a viewer’s perception is bound to shift when the GIF is observed from different angles of the camera. For instance, at 10? above the horizontal, you should be able to visualize the image flipping anti-clockwise 60% of the overall time. If the demo is repeated with 10? beneath the horizontal, you should be able to see the object rotating clockwise for the time’s 60%. 

In this context, ‘horizontal’ refers to the line that is level with the viewer's eyes or parallel to the ground. So, if the viewer is looking straight ahead, the horizontal line would be at eye level. If they tilt their head up by 10°, they're looking slightly above the horizontal line, and if they tilt their head down by 10°, they're looking slightly below the horizontal line. 

To wrap it up, our brain has a tendency of staring at the ground to see if there is anything dangerous there. Things, including those that could hurt us, are more likely to sit on the ground, Niko Troje, Director for BioMotion Lab at Queens University, says. It's to our advantage to quickly recognize a snake stretched across a dark path, for instance. So when presented with ambiguous visual information, people tend to register the images as though they're looking downward. And that is why the majority sees the GIF as flipping clockwise. 


 

Aishani Purkayastha

Best served with sarcasm.