To examine visual spatial attention in autism, we use a paradigm of rapid serial visual presentation. Coloured flashes appear at a rate of 9 per second in the upper left and right visual quadrants.

At any given time, one of these locations is attended, and the other is ignored.

The target colour in the attended hemifield cues not only an overt behavioural response - a finger movement - but also a covert shift of attention to the opposite hemifield.

`Functional Anatomy of Compensatory Processing in Autistic Attention: Complementary Roles of Selection and Suppression', Matthew Belmonte, 1 November 2002