Vision is arguably the most important sense for most human beings; and, as could be expected, several parts of the brain are involved in processing visual information (Bear, Connors, & Paradiso, 2001). As vision is the main provider of information about threats and opportunities in the world, it to a large extent drives behaviour. People are not passive onlookers to life, though, but have expectancies derived from earlier experiences; people have goals, and hence, intentions. These goals and intentions set up a framework for what will be necessary to attend to, and "each of us literally chooses, by his ways of attending to things, what sort of universe he shall appear himself to inhabit" (James, 1890, p. 424). Hence, there is a reciprocal relationship between the available information and what is attended to. It seems like this reciprocal relationship can also be found at a neuronal level. Only about 15% of the input to the lateral geniculate nucleus (LGN) comes from the retina; 80% of the excitatory synapses in the LGN come from the primary visual cortex (Bear, Connors, & Paradiso, 2001). It has been argued that top-down expectations selectively amplify features that are attended to, while at the same time dampening others (e.g., Grossberg, 1998). .
Attention seems to be intimately linked to consciousness. We cannot attend to something (be it a physical object or a thought) without at the same time being conscious about the object of attention. Thus, it seems reasonable that the neuronal substrates of attention correlate with those of consciousness. Given that all the information available from the retinas do not enter consciousness, and that that being attended to usually does, it seems like the study of visual attention may give a glimpse into the brain mechanisms of consciousness. .
During saccadic eye movement, visual processing is suppressed (Volkman, Riggs, & Moore, 1980). Thus, visual information comes into the perceptual processing system in discrete chunks.
