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Thursday, 26 September 2013

What is consciousness?

Consciousness, on first glance, seems like a relatively easy concept to understand. It is something we have when we are awake, but which leaves us when we fall asleep, are knocked out, or faint. It is that feeling of awareness, of understanding our own being, the ability to feel and understand the world around us. But when we look a little closer, consciousness becomes a much murkier concept, and much less easy to comprehend.

Artist's impression of the concept of consciousness
Dualism views the mind and body as two distinct and separate things. Image credit: conkling
Rene Descartes, the 17th century French philosopher, argued that consciousness was the domain of the mind, and that this was a separate entity to the body, a belief known as Dualism. He suggested that the two interacted via the pineal gland in the brain, but this led to a problem; How is it possible that something non-physical like the mind can affect something physical like the brain? Partly because of this so-called ‘mind-body’ problem, most modern researchers in consciousness reject the dualist approach, and treat consciousness as something that arises from physical processes in the brain.

Although it is a difficult concept to define, most of us are happy to agree that other humans also have consciousness, much like our own, but plants, mountains and other inanimate objects do not. But how do we know this? Although other people may look like us, and behave like us, there is no way we can know that they have the same experiences as us - we cannot know for sure that they are not ‘philosophical zombies’, with normal behaviour but no subjective experience of the world at all.

Originally the territory of philosophers, recently more scientists have begun investigating the phenomenon of consciousness. For example, it is possible to invoke conscious perceptions, or ‘qualia’ that are not physically present, or for subjects to remain unaware of objects that are ‘visible’. This allows researchers to isolate the brain processes involved in consciously experiencing something, rather than those simply produced by the presence of an object in your visual field.

The "invisible gorilla" video shows an experiment in which subjects display selective attention.


One way of separating input from perception is using visual illusions, such as the Necker cube, which seem to flip between two different interpretations, even though the image does not change.

Rubin's Vase seem to flip between two different interpretations, even though the image does not change.
What can you see?
 Image credit: magicpainting
Experiments on macaque monkeys1 showed that they too see the cube ‘flip’, so monkeys can be used as a model for our own perception. A similar change in perception also occurs when different images are presented to each eye - a technique known as binocular rivalry. Interestingly, the neurons that can be correlated with which image the monkey perceives at a specific time seem to be in the higher visual areas- those involved in more complex visual processing, such as attention and categorisation, rather than the initial response of light falling on the retina. The low level areas, however, which respond simply to the stimulus, stay constant. The monkeys’ changing visual experience or ‘qualia’, as the image seems to flip from one to another, is completely separate from the signals that enter the brain from the eye.

Functional Magnetic Resonance Imaging (fMRI) studies allow us to see the activity of the human brain, non-invasively and in real time, as people are performing various tasks. fMRI studies in humans have shown that both low level visual areas, and higher level areas such as the fusiform face area (a high level visual area that responds specifically to faces) respond to the qualia, not the actual stimulus - their activity changes as the person sees the cube flip from one orientation to another, even though the picture is not actually changing2. This suggests that while there are parts of the brain that respond to what is actually present in the world, the inner world we construct for ourselves is far more important.

Experimentally, it is possible to ask human subjects to report their conscious understanding of a task, and compare this to their performance on a task. For example, in priming tasks, subjects are influenced by a word or picture presented so quickly that they are not consciously aware of having seen it3. Priming can change how people complete word fragments e.g. so_p is likely to be completed as soap if you have seen the word wash unconsciously, or as soup if the word eat was presented4. It has also been seen to affect peoples’ liking of random shapes (if one is linked with a happy face and another with an angry face, presented subconsciously)5, and even made people walk more slowly, if they are primed with words relating to elderly people6.

These findings make it clear that we are not conscious of everything that goes on in our surroundings, or even everything that is happening in our brains.So why do some things reach consciousness while others don’t? And what is consciousness even for? Did it evolve because it had a survival advantage, or is it simply epiphenomena - a side effect of the complex calculations our brains complete every second of every day simply to keep us alive? This is what Philosopher David Chalmers termed the ‘hard problem’ of consciousness, as there are no obvious experiments that will help us to answer this question.

Some philosophers, such as Dan Dennett, argue that the ‘hard problem’ is an illusion, much like those we see when watching a magician on stage. He claims that by solving the easy problems; understanding how we attend and respond to the world around us, what changes when we sleep, and how we integrate perceptions and behaviour, we will find that the hard problem simply disappears. Whether this is true is not yet clear, but what is for sure is that solving the problem of consciousness is not going to happen overnight. For now at least what consciousness is, and why we have it, is definitely a Thing We Don’t Know!

References
why don't all references have links?

[1] Backus, Benjamin T, and Qi Haijiang. Competition between newly recruited and pre-existing visual cues during the construction of visual appearance. Vision research 47.7 (2007): 919-924.;
[2] Frith, Chris, and Raymond J Dolan. Brain mechanisms associated with top-down processes in perception. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352.1358 (1997): 1221-1230. PMCID: PMC1692001
[3] Bornstein, Robert F, Dean R Leone, and Donna J Galley. The generalizability of subliminal mere exposure effects: Influence of stimuli perceived without awareness on social behavior. Journal of personality and social psychology 53.6 (1987): 1070.
[4] Neely, James H. Semantic priming and retrieval from lexical memory: Evidence for facilitatory and inhibitory processes. Memory & Cognition 4.5 (1976): 648-654. DOI: 10.3758/BF03213230
[5] Murphy, Sheila T, and Robert B Zajonc. Affect, cognition, and awareness: affective priming with optimal and suboptimal stimulus exposures. Journal of personality and social psychology 64.5 (1993): 723.
[6] Cesario, Joseph, Jason E Plaks, and E Tory Higgins. Automatic social behavior as motivated preparation to interact. Journal of personality and social psychology 90.6 (2006): 893. DOI: 10.1037/0022-3514.90.6.893