Article
How can a process be measured from the outside while the experience itself is known from the inside? A color, a sound, a pain, a thought: each is more than a signal when someone lives through it. What do researchers mean when they call these different things consciousness?
A word that holds several questions
Consciousness is not one question with one obvious measurement. Researchers may ask whether someone is awake, what they perceive, whether information is available for reasoning and report, or whether they can monitor their own thoughts. These questions overlap, but they are not interchangeable. A person might respond to a stimulus without being able to describe how the response formed. Each case points to a different kind of access.
One influential framework separates nonconscious processing, access to information, and self-monitoring. Dehaene, Lau, and Kouider use C0 for nonconscious processing, C1 for information made globally available, and C2 for reflective awareness of one’s own mental state. The vocabulary helps experiments ask narrower questions. It does not prove that these categories exhaust subjective experience or certify consciousness in a machine.[2]
What observation can tell us
Experiments connect theories to reports, behavior, and brain activity. Reviews map several proposed accounts, including global neuronal workspace and integrated information theories, and compare the kinds of observations each is designed to explain. A measured brain pattern might track conscious access, enable it, or follow it. Those possibilities require different tests, so a correlation is a beginning for explanation rather than its final step.[1]
The idea of a single ladder of consciousness is also disputed. Bayne, Hohwy, and Owen argue that talk about levels can combine wakefulness, richness of experience, and access to information, even though those dimensions need not rise and fall together. Their analysis is a conceptual review, not a clinical scale. It warns against treating one score as a complete account of another person’s experience.[3]
Where current theories stand
In 2025, the COGITATE Consortium reported a preregistered adversarial test of predictions from global neuronal workspace and integrated information theories. The tests challenged predictions from both. That result matters because competing accounts faced an effort to distinguish them, but it does not choose a winner or resolve the larger metaphysical question of why experience feels like anything.[4]
A theory can explain when information becomes available and still leave open whether it has explained subjective feeling. That further question is the focus of the hard problem. Neural studies ask how ordinary human awareness changes with brain function, while careful definitions help keep those findings attached to the question they actually test.[1][4]
Why the distinctions matter
Definitions shape both experiments and conclusions. Calling every complex behavior consciousness hides meaningful differences. Treating a first-person report as a flawless measurement hides its limits. A careful account makes room for evidence from the outside while recognizing that reports, neural activity, and lived experience answer related but different questions.
When we ask whether a person, an animal, or a machine is conscious, which evidence should matter most: flexible access to information, a report, a pattern of brain activity, or the felt point of view those measures are meant to illuminate?