Attention is essential for our everyday functioning. In order to remember information, you generally need to pay attention to it. This process of focused awareness is accompanied by readiness of the central nervous system (CNS) to respond to specific stimuli. Most theories of attention compare it to a filter that screens out a lot of stimuli while permitting a select few to go into our conscious awareness so that we can regulate our own behaviour. What remains unclear is at what point (i.e. early, during sensory input or later, after the brain has processed the meaning of the input) the filter is located in the information processing system. Models of attention are thus often described as early-selection or late selection theories. It is currently thought that the attention filter may be flexible rather than fixed.