Normally, when people attend to particular locations in space, a lot of this withdrawal from things elsewhere occurs during the early stages of sensory processing. From the standpoint of efficiency, this computational strategy makes good sense: what's the point in processing a stimulus at all if you know in advance that you're not interested in the result?

`Physiological Studies of Attention in Autism: Implications for Autistic Cognition and Behaviour', Matthew Belmonte, 26 January 2002