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Choose one of the people closest to you... maybe your partner, a parent, a friend or one of your own children.

Now picture them in your head. Close your eyes and remind yourself exactly what they look like.

For most of us that's a natural and easy thing to do - but if you have aphantasia you'd find that very difficult, probably even impossible.

5 live's Chris Warburton spoke to the scientist who coined the phrase - and people who experience the condition - to find out more.