Out of body experiences and grasping the ungraspable

This week’s ABC Radio National’s All in the Mind discusses what happens in the brain during out of body experiences, and why actions can be accurate even when our perceptions are not.

The first interview is with neurologist Olaf Blanke who discusses some of his recent compelling research, including a virtual reality experiment to induce out-of-body touch sensations in healthy participants and one with implanted brain electrodes to trigger full-blown out-of-body experiences in patients undergoing neurosurgery.

The second interview is with psychologist Melvyn Goodale, famous for his work on distinguishing the visual streams in the brain: the dorsal stream and the ventral stream.

Some of the most striking and important results from this work come from patients who have suffered damage to one or the other stream.

In the programme, Goodale talks about brain-injured patient DF, who can correctly and accurately grasp objects she cannot consciously ‘see’. The opposite has been found in other patients, who can accurately see and describe objects they cannot accurately grasp.

This suggests that these two visual pathways, although complimentary, are specialised for different things, one for identifying objects, and the other for working out where they are and how to manipulate them.

The different function of the two pathways can also be demonstrated in healthy people as well.

You may recognise the visual illusion on the left, sometimes called the Titchener or Ebbinghaus illusion. The two circles in the middle are actually the same size, but look different due to their context.

Researchers have created a graspable version of the illusion by putting hoops on a flat surface.

When they’ve measured how people adjust their fingers to pick up the middle circles, they find that we don’t over or underestimate the size. Our fingers are always perfectly adjusted to the actual size.

In other words, it seems that while our perception is fooled by the illusion, our actions aren’t, showing how the specialisation of each visual stream can be seen in everyone.

There’s now a minor cottage industry of research attempting to understand exactly what influences the effect.

UPDATE: “All in the Mind has been honoured with the Grand Award at 2008 New York Radio festivals for best entry across all categories, as well as a Gold World Medal in the Health / Medical category”. – I’m sure it won’t come as a surprise to most Mind Hacks readers but fantastic to have it recognised by the non-initiated!

Link to AITM on out-of-body experiences and other tricks of consciousness.

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