Can imagination affect what you see?

Does our imagination affect what we see and hear?

Our perception, what we understand about what's going on in the world around us, is a combination of all of our senses. What we see and what we hear comes together to tell us what's going on. But, if our senses disagree with each other, we tend to come up with the wrong answer. 

One famous multisensory illusion, called the McGurk illusion, shows that if we hear someone saying the sound /ba/, but we see them saying /ga/, we think they're saying /da/. So, when our senses are disagree we amalgamate them and believe the position in the middle. This week researchers at the Karolinska Institute have published a paper in Current Biology that asked, 'What about our imagination?'  If we imagine hearing something, could it affect what we see and play into these multisensory illusions?. 

They recreated three famous perception experiments with one element imagined rather than seen or heard to see if they still work under these conditions. One experiment showed a cross of ramps going past each other with a disc at the top of each ramp. As the discs ran down the ramps the participants were asked to imagine a sound happening, some at the point where the discs passed each other, some before and some afterwards. Those that imagined the sound happening just as those discs passed each other thought that they saw the discs bouncing back off each other - the illusion still worked, even though the sound was imagined.

Similarly, they re-did the McGurk illusion. They asked participants to imagine the sound /ba/, showed them a video someone saying /ga/ and they still perceived /da/. These results show that multi-sensory illusions are still effective even if of those senses is imagined rather than actually happening. Researchers have suggested that this implies neural networks which register perceived and imagined senses have some cross over, so what we imagine is included in our perception of the world. They hope a greater understanding of this process will be able to contribute to treatment of some psychiatric disorders, like Schizophrenia, where people are unable to distinguish between what is real and what is imagined.