Source: Kalhh via Pixabay

We can learn much about psychology by paying to what people do in the world and then exploring it under more controlled conditions. One way that can be done quite effectively, it turns out, is by using the work of magicians.

At the risk of spoiling the fun, magicians don’t actually make things disappear or make one card change into another. Instead, they engage in actions that misdirect people’s attention in ways that prevent them from seeing how the magician has created the illusion of change.

One thing that seems to lead people to miss changes is a switch in direction. A magician might wave a card in the air in front of an audience and, when switching direction from left to right or vertical to horizontal, also make a change in the of the card. Suddenly, it seems that one card has become another.

Is the switch in direction really the important element here, or is it just that magicians perform their actions so quickly that people don’t see them?

This question was addressed in a set of studies by Richard Yao, Katherine Wood, and Dan Simons reported in the March 2019 issue of the journal Psychological Science.

They had people look at a computer screen and try to detect a change in the orientation of something called a Gabor patch. A Gabor patch is essentially circle containing black and white bars that point in a particular direction. For example, they might point at an angle that is roughly 2 o'clock to 8 o’clock.

To make the task a bit more difficult, there were six of these patches on the screen at the same time. At some point, one of these patches shifted from one orientation (say 2-to-8 o’clock) to another (perhaps 4-to-10 o’clock). The participants' job was to say which patch moved after the trial was over.

Here’s where the motion comes in.

The collection of patches shifted between moving horizontally across the screen and moving vertically. The change in the orientation of one of the patches happened either while the collection was moving horizontally or at the moment when the movement shifted from horizontal to vertical.

Participants correctly detected the change in orientation of the patch about 86% of the time when it happened while the patches were moving horizontally. When the change happened at the moment of the switch in direction, they detected the change only about 26% of the time. The researchers repeated this study a few times with some variations and always found that changes in orientation were harder for people to see at the moment of a shift in direction that while the patch was moving in a straight line. In one variation, they used eye tracking to make sure that people stayed fixated on the screen during the change in direction.

What makes this result impressive is that people are failing to notice a shift even though they are looking in the direction of what is changing. People’s attention to detail is drawn away by the change in direction of movement.

One way to think about this is that in the real world, the identity of objects generally does not change suddenly. So, the human visual system is not set up to make sure that the object you’re looking at remains the same one the entire time you’re looking at it. Instead, the visual system detects important shifts in —and a change in the direction of motion of something in the world is an important shift. Magicians exploit this aspect of visual attention to create illusions.

Luckily, even when you know this about attention, illusions still work. Understanding attention a bit better need not ruin your enjoyment of a good magic show.