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# 3D Blindness

3D Blindness is an inability to visualise solid objects accurately. It also applies to the inability to anticipate how a situation in three dimensions is changing, which is important in driving and in sports.

Geoff Hinton first wrote about this phenomenon in 1979.[1][2] It has been found that 96% of the population have not developed the ability to visualise in three dimensions.

It was first tested with final year computer graphics students in the US, but the tests have been given in many other countries (Australia, New Zealand, India, Europe) to a total of over 3,000 subjects, with almost identical results.

## Tests and results

First Test that they were given: Visualise a cube with about half metre side. Hold opposite faces of the cube between your hands. Concentrate on the cube. Press and feel how hard it is. Tip it from side to side and feel the weight change.

They were then asked to balance the cube on one corner, (not an edge), on the middle of a sheet of card on the table. They used one hand on the top corner to balance it.

They were asked to use their free hand, to touch and name each of the other corners (ignoring top and bottom) with letters A, B,..... , and were asked to write down the last letter reached?

Some subjects were unable to do this, and most reached D (all in a square). Only 4% touched the 6 corners

They were then asked to imagine pushing the corner through the card until it made a hole about 5cms across. They were asked to draw the shape of the hole

95% drew a square or a diamond, 1% drew a circle, and 4% drew the triangle. The circle was usually drawn by women, though it was more common with children

The brain had, apparently, applied one of its tricks to get a quick answer, but has drawn its rules from attributes of a cube in a more usual position (where turning through a right angle, preserves the picture). This time it has misfired; the square hole would be obtained from an octahedron (two square based pyramids base to base), not with a real cube.

When they were shown that they hole was a triangle they then attemptd the process of pushing the cube through the card. They noted that the shape of the hole gets bigger, but in general could not continue the process.

The second test had a different setup: They were asked to visualise a tub is full of hundreds of spherical marbles, each with two marks designating its axis, with the axes are in all directions. They were asked to concentrate on only the marbles with an axis horizontal or vertical. They were asked were there a) more vertical than horizontal? b) more horizontal than vertical? c) or are they about the same?

Most subjects thought that they were about the same. Apparently the brain stays in two directions, where horizontal and vertical are shown as directions at right angles.

This inability to see in three dimensions has implications for road safety,[3] as well as sport.

A one-day training course was given in course 42, SIGGRAPH 2001.[3]

## References

1. Geoffrey Hinton, "Some Demonstrations of the effects of Structural Descriptions in Mental Imagery", Cognitive Science 3, 221-250, 1979
2. G Hinton, "The horizontal–vertical delusion", Perception Vol 16 No 5, 1987
3. Bob Parslow and Geoff Wyvill, Seeing in 3D, Course 42, SIGGRAPH 2001, Los Angeles 2001

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