Table 1.

Definitions relevant to consciousness

Terms	Explanation
Easy vs. hard problem of consciousness	This distinction was drawn by philosopher David Chalmers. “Easy” problems of consciousness (which are easy in principle only) include understanding the neural basis of feature detection, integration, verbal report, etc. The hard problem is the problem of experience; even if we understand everything about neural function, it is not clear how that would explain subjectivity.
Awareness	Cognitive neuroscientists and philosophers use the term “awareness” to mean only subjective experience. In clinical anesthesiology, the term awareness is (inaccurately) used to include both consciousness and explicit episodic memory.
Wakefulness vs. awareness	Wakefulness refers to brain arousal, which can be manifest by sleep–wake cycles and can occur even in pathologic conditions of unconsciousness such as vegetative states. Thus, being awake is dissociable from being aware.
Phenomenal vs. access consciousness	Phenomenal consciousness is subjective experience itself, whereas access consciousness is that which is available to other cognitive processes (such as working memory or verbal report).
External vs. Internal consciousness	External consciousness is the experience of environmental stimuli (such as the sound of an orchestra), whereas internal consciousness is an endogenous experience (such as a dream state).
Consciousness vs. responsiveness	An individual may fully experience a stimulus (such as the command “Open your eyes!”) but not be able to respond (as when a patient is paralyzed but conscious during surgery).
Levels of consciousness vs. contents of consciousness	Levels of consciousness include distinctions such as alert vs. drowsy vs. anesthetized, whereas the contents of consciousness refer to particular phenomenal aspects such as a red rose vs. a blue ball.