Psychology describes and attempts to explain consciousness, behavior, and social interaction. Empirical psychology is primarily devoted to describing human experience and behavior as it actually occurs. Since the 1980s, psychology has begun to examine the relationship between consciousness and the brain or nervous system. It is still not clear how these interact: does consciousness determine brain states or do brain states determine consciousness - or are both going on in various ways? Or, is consciousness some sort of complicated 'illusion' that bears no direct relationship to neural processes? Perhaps to understand this, it is necessary to define "consciousness" and "brain state". An understanding of brain function is increasingly being included in psychological theory and practice, particularly in areas such as artificial intelligence, neuropsychology, and cognitive neuroscience.