The raw immediacy of our waking lives leaves us feeling as though our five senses give us a true, undistorted perception of the world. But a catalogue of psychology experiments has shown this sense of experiencing the world “as it is” couldn’t be further from the truth. Now with the latest demonstration of the tricks our minds play, Johahn Leung and colleagues have reported that moving our heads fast has the effect of compressing auditory space – that is, sounds emitted just before a head turn are sucked perceptually towards the target of the head movement.
Participants held their bodies still while shifting their heads as fast as possible to a light that appeared either 30 degrees to the left or right. Just before the start of their head turn, a sound was emitted from a mobile speaker that could be located a range of distances beyond or nearer than the light. Judged against a second comparison sound, the participants consistently mislocated the first sound as being nearer the target of their head turn than it really was. It’s as though auditory space was compressed towards the light at the moment just before they moved their heads.
The finding replicates a similar spatial compression effect that occurs just before people make fast saccadic eye movements. In this case, experts think the compression is caused by brain cells adjusting their receptive fields in anticipation of where the eyes are going to be pointing after they’ve finished moving. Leung and colleagues said a similar process probably explains the current findings.
In a final twist, the compression of auditory space didn’t occur if participants indicated the location of the sound by pointing their nose in its direction. Indicating the sound location in this way (rather than by perceptual comparison with a second sound) probably relies on the brain’s action pathway, which is known to be less affected by perceptual illusions.
Leung, J., Alais, D., Carlile, S. (2008). Compression of auditory space during rapid head turns. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0710837105