5.6.1. In Action
We can see the interaction of information hitting two senses at once in all sorts of situations. People sound clearer when we can see their lips [Hack #59] . Movies feel more impressive when they have a sound track. If someone gets a tap on one hand as they simultaneously see two flashes of light, one on each side, the light on the same side as the hand tap will appear brighter.
Helge Gillmeister and Martin Eimer of Birkbeck College, University of London, have found that people experience sounds as louder if a small vibration is applied to their index finger at the same time.2 Although the vibration didn’t convey any extra information, subjects rated sounds as up to twice as loud when they occurred at the same time as a finger vibration. The effect was biggest for quieter sounds.
5.6.2. How It Works
Recent research on such situations shows that the combination of information is wired into the early stages of sensory processing in the cortex. Areas of the cortex traditionally thought to respond to only a single sense (e.g., parts of the visual cortex) do actually respond to stimulation of the other senses too. This makes sense of the fact that many of these effects occur preconsciously, without any sense of effort or decision-making. They are preconscious because they are occurring in the parts of the brain responsible for initial representation and processing of sensationanother example (as in [Hack #15] ) of our perception not being passive but being actively constructed by our brains in ways we aren’t always aware of.
Macaluso et al.3 showed that the effect can work the other way round from the one discussed here: touch can enhance visual discrimination. They don’t suggest that integration is happening in the visual cortex initially, but instead that parietal cortex areas responsible for multisensory integration send feedback signals down to visual areas, and it is this that allows enhanced visual sensitivity.
Taken from : Mind Hacks
