Out Of Sync: How The Brain Deceives You By Joining Sounds And Images

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Out Of Sync: You must have learned in high school physics classes that sound and light travel at different speeds. Imagine how complicated it would be to perceive the world with this “delay”. Luckily for us, the human brain has compensatory mechanisms that help us to synchronize different stimuli, such as temporal recalibration. The phenomenon was the subject of a new study carried out at McGill University in Montreal, Canada – which revealed how the mechanism works.

The research team found that temporal recalibration depends on brain signals that constantly adapt to capture samples from our environment, ordering and associating sensory stimuli that actually compete with each other.

How the study was done

The researchers recruited volunteers to observe short flashes of light linked to sounds that exhibited a variety of delays. Subsequently, they asked these people to report whether they thought that both occurred simultaneously. The participants performed the task inside a magnetoencephalography (MEG) machine – a technique for mapping brain activity by detecting the magnetic field produced by the organ’s electric currents.

MEG recorded and was able to visualize the volunteers’ brain waves with millisecond precision. The pairs of audiovisual stimuli changed each time, with sounds and images presented closer or more distant in time – and with random presentation orders.

The researchers found that the volunteers’ perception of simultaneity between the pair of audiovisual stimuli was strongly affected by the perceived simultaneity in the pair of stimuli that came before it. For example, when a sound followed by an image was presented with a millisecond interval – and was perceived as out of sync – the receiver is very likely to report the next pair of audiovisual stimuli as being in sync, even if it is not.

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