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A man whose brain was damaged by a stroke now sees all objects and people about a third smaller than their actual size.

The 66-year-old had a stroke in December 2017 that cut off oxygen to the back right of his brain.

Afterwards, he noticed that everything appeared strangely smaller than normal. For example, at a clothing shop, he mistakenly picked up an extra-large T-shirt thinking it was his usual medium size. Doorways suddenly looked too small to fit through, and he thought his wife must have washed their curtains in hot water because they looked like they had shrunk.

By comparing familiar objects and people with his memory of their actual sizes, he realised they now all appeared about 30 per cent smaller.

To try to understand what was going on, Nils van den Berg at the University of Amsterdam in the Netherlands and his colleagues devised a series of tests for the man, who they refer to as DN.

In one test, DN had to visually estimate the size of 10 different cubes on a table in front of him. Consistent with his subjective experience, he estimated each cube to be about 30 per cent smaller than 11 other people did.

Missing vision

This distorted size perception seemed to be related to problems with DN鈥檚 left visual field. For example, when he looked at two cubes sitting next to each other, he thought the left cube was smaller than the right one, even when it was the same size or bigger. Computer tests showed that he also had difficulties identifying the shape, location and motion of objects in his left visual field.

This makes sense, since information from the left visual field is usually processed by the back right of the brain, which is where DN鈥檚 stroke damage occurred, says van den Berg.

DN鈥檚 brain may be trying to compensate for this damage by knitting together the remaining information from his diminished left visual field with that from his intact right visual field, says van den Berg. 鈥淭he result is apparently a smaller, but symmetrical and meaningful representation of the outside world,鈥� he says.

A handful of other people have also reported seeing things as smaller or bigger than normal or even upside down after damage to the same brain region. However, the exact mechanism underpinning these size distortions is still unknown, says van den Berg.

DN has now learned ways to cope with his altered perception of the world. For example, he estimates the size of unknown objects 鈥� like doorways 鈥� by comparing them with familiar objects. And when he cycles or drives, he sticks close to the side of the road so there鈥檚 no risk of colliding with oncoming vehicles. 鈥淗e gets tired easily but otherwise he is doing quite well,鈥� says van den Berg.

The case demonstrates how the brain is capable of using whatever information it has available to create a coherent model of the world, he says.