For most of you, the ability to recall what your parents faces look like is no bother at all. But for some, this task is impossible. A few years ago, researchers finally described a condition in which people cannot imagine things in their "mind’s eye", called aphantasia.
Only described recently, a lot of people have grown up assuming that when people asked them to “picture” something in their mind, they were simply talking metaphorically. But now researchers are starting to unravel the truth behind aphantasia, which could affect up to one out of every 50 people (although this is a rough estimate).
One of the hardest things to determine is whether or not aphantasia is actually real, something that a recent study published in the journal Cortex set out to solve. The problem stems from the fact that I cannot know what you can or cannot see, and vice versa. This means that when people are asked to imagine things and then describe that they see, there is no objective measure. We could be seeing the same thing and describing them differently, or seeing different things and describing them the same.
To test this, the researchers devised an experiment known as binocular rivalry. Participants were given a pair of 3D glasses, where one lens shows a green circle with horizontal lines and the other lens shows a red circle with vertical lines. The binocular rivalry illusion induces a state where the images in the two eyes are incongruent and what we see fluctuates between the different images, in this case the colored circles. Before putting these on, however, the participants were asked to imagine one of the colored circles beforehand. If they can indeed picture things in their mind, then the colored circle they were asked to imagine should become the dominant image they see. Those who could not imagine things reported no effect on the binocular rivalry illusion.