Consciousness: What It Is and How Science Studies It

Consciousness is at once the most familiar and the least understood fact about the mind. You are using it to read this sentence, yet science still cannot fully explain why physical processes in the brain are accompanied by experience at all. Psychology and neuroscience have nevertheless made real progress by studying consciousness the way they study anything else: by finding what varies with it, what breaks it, and what its neural signatures look like (see cognitive neuroscience for the methods).

Table of Contents

1. Defining Consciousness
2. States and Levels
3. The Major Theories
4. What Breakdowns Reveal
5. How Consciousness Is Studied
6. Why It Matters in Psychology
7. Key Takeaways
8. References

Defining Consciousness

William James gave the description that still frames the field: consciousness is not a chain of separate pieces but a stream—continuous, personal, and always changing (James, 1890; see William James). Modern writers usually distinguish:

• Phenomenal consciousness — what experience is like: the redness of red, the ache of a tooth.
• Access consciousness — information being globally available for reasoning, reporting, and guiding action (Block, 1995).

Philosopher David Chalmers sharpened the agenda by separating the "easy problems"—explaining functions like attention, reportability, and behavioral control—from the "hard problem": why any of this is accompanied by subjective experience (Chalmers, 1995). The easy problems are hard science; the hard problem remains open.

States and Levels

Consciousness is not binary. It varies on at least two axes:

• Level (overall responsiveness): from alert wakefulness down through drowsiness, sleep, anesthesia, and coma.
• State (the flavor of experience within a level): dreaming, flow, meditative absorption, or drug-altered states are all "conscious" but organized differently.

This two-dimensional picture explains a classic surprise: dreaming sleep is a high-arousal, internally generated conscious state—the brain is not "off" at any point in the night.

The Major Theories

No theory has won, but the leading contenders make different testable bets:

The honest summary: theories agree that consciousness involves widespread, integrated brain activity differing from unconscious processing, and disagree about what, in principle, makes the difference.

What Breakdowns Reveal

Pathology is where consciousness science earns its keep:

• Blindsight (link): patients with primary visual cortex damage deny seeing stimuli they can nevertheless guess accurately—vision without visual awareness (Weiskrantz, 1986).
• Split-brain patients (link): after the hemispheres are surgically separated, the two halves can respond to different contents—one of the strongest hints that consciousness depends on integrated, distributed coordination.
• Anesthesia and comas show that level of consciousness can dissociate from wakefulness: behavior and awareness come apart in both directions.

How Consciousness Is Studied

Because consciousness cannot be observed directly, researchers use the contrastive method: hold the stimulus constant and compare brain activity when it is perceived versus not perceived. Classic tools include masking, binocular rivalry (one image fades from awareness while remaining on the retina), and attentional manipulations. Findings consistently link conscious report with late, widespread, recurrent brain activity rather than early sensory cortex alone.

First-person methods matter too: systematic introspection has known limits (much of processing is inaccessible), but report, confidence ratings, and trained self-observation remain irreplaceable data sources. Contemplative traditions supply another angle—mindfulness research examines trained attention to experience itself.

Why It Matters in Psychology

• Attention and working memory mark the border of awareness: unattended, well-processed information often never becomes conscious (see attention and working memory).
• Ethics: disorders of consciousness, fetal and animal consciousness, and anesthesia standards all depend, practically, on where science draws these lines.
• Mental health: altered states—rumination, dissociation, depersonalization—are clinically significant variations in the organization of consciousness.

Key Takeaways

1. Consciousness is a stream of experience, decomposable into phenomenal (what it feels like) and access (what the brain can use) aspects—with a "hard problem" that remains open.
2. It varies both in level (alert → anesthetized) and state (waking, dreaming, flow, meditative).
3. Global workspace theory and integrated information theory lead a contested field; both predict widespread, integrated neural activity for conscious content.
4. Blindsight, split-brain findings, and anesthesia show awareness can dissociate from processing, behavior, and wakefulness.
5. The contrastive method—same stimulus, awareness on versus off—is the workhorse of consciousness science.

References

• James, W. (1890). The principles of psychology. Henry Holt.
• Block, N. (1995). On a confusion about a function of consciousness. Behavioral and Brain Sciences, 18(2), 227–247.
• Chalmers, D. J. (1995). Facing up to the problem of consciousness. Journal of Consciousness Studies, 2(3), 200–219.
• Baars, B. J. (1988). A cognitive theory of consciousness. Cambridge University Press.
• Dehaene, S., & Changeux, J.-P. (2011). Experimental and theoretical approaches to conscious processing. Neuron, 70(2), 200–227.
• Tononi, G., & Koch, C. (2015). Consciousness: Here, there and everywhere? Philosophical Transactions of the Royal Society B, 370(1668), 20140167.
• Weiskrantz, L. (1986). Blindsight: A case study and implications. Oxford University Press.