In the previous chapters, we have dealt exclusively with the part of attention that is concerned with visual processing. This part is the best investigated one in human behavior, probably because vision is the sense using the most capacity in the human brain: the 32 representations of the retina occupy more than half of the whole cortex [Kandel et al., 1996] and the primary visual cortex V1 has the richest architecture of all cortical areas [Zeki, 1993].