To understand this, we divide consciousness into two part \cite{Chalmers_1998}. The first part is the 'easy problems of consciousness' which include the following phenomena: the ability to discriminate, categorize, and react to environmental stimuli; the integration of information by a cognitive system; the reportability of mental states; the ability of a system to access its own internal states; the focus of attention; the deliberate control of behaviour; and the difference between wakefulness and sleep. On the contrary, the hard problem refers then to the problem of explaining why and how sentient organisms have qualia or phenomenal experience.