The sensory systems supply the information that is used to build a represen
tation of our external world. However, the amount of information provided b
y highly evolved sensors such as the eyes of higher animals, exceeds the ne
rvous system's capacity. Attention serves as one of the main selection mech
anisms that allows these animals and humans to concentrate processing resou
rces on the most relevant information. Here we review selected findings and
present some of our own data in macaques about how this selection process
effectively and often without the individual's awareness prevents irrelevan
t information from reaching later stages of processing.