Western philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. These issues remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively. Some basic questions include: whether consciousness is the same kind of thing as matter; whether it may ever be possible for computing machines like computers or robots to be conscious; how consciousness relates to language; how consciousness as Being relates to the world of experience; the role of the self in experience; whether individual thought is possible at all; and whether the concept is fundamentally coherent.
Recently, consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology, neuropsychology and neuroscience. The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness. The majority of experimental studies assess consciousness in humans by asking subjects for a verbal report of their experiences (e.g., "tell me if you notice anything when I do this"). Issues of interest include phenomena such as subliminal perception, blindsight, denial of impairment, and altered states of consciousness produced by alcohol and other drugs, or spiritual or meditative techniques.
In medicine, consciousness is assessed by observing a patient's arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli. Issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted. The degree of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale.