By Kate Douglas / Source: New Scientist
Earlier this year I found myself thinking about thinking.
Specifically, what is it that makes the human mind so special? Like many people, I have always believed that the answer lies in our capacity for conscious thought. But listening to speakers at a recent Ernst Strungmann Forum in Frankfurt, Germany, I began to wonder if there might be more to it than that.
It was a discussion entitled "Better than conscious" that had me intrigued. The more I listened to what the assembled scientists had to say and talked to them about their work, the more it seemed that our higher consciousness alone is not what sets us apart from other animals.
In fact, far from playing second fiddle to the conscious mind, subconscious thought processes may play a crucial role in many of the mental facilities we prize as uniquely human, including creativity, memory, learning and language.
Modern notions of the subconscious were invented by Sigmund Freud as part of his now-discredited theory of psychoanalysis. These days the subconscious is on a firmer scientific footing - although many neurobiologists avoid the word "subconscious", preferring "non-conscious", "pre-conscious" or "unconscious" to describe thought processes that happen outside consciousness.
Where Freud and his followers saw the subconscious as little more than an emotional and impulsive force in a constant tug of war with the more logical and detached conscious mind, we now know that this view is too simplistic. Our subconscious is not an unthinking autopilot that needs to be subjugated by rationality, but a purposeful, active and independent guide to behaviour.
Some scientists go so far as to believe that it is responsible for the vast majority of our day-to-day activity and that we are nothing more than "zombies" guided by our subconscious. This is an extreme point of view, but in the past few years, researchers trying to understand the nature of human consciousness and how it differs from the subconscious have made some surprising discoveries. Put the findings of many studies together and another picture emerges. There is more to being human than consciousness.
To get to this new view of the subconscious, neuroscientists and psychologists have had to fight hard to overcome a major barrier. So far, there is no reliable way to distinguish between conscious and subconscious thought processes. They can be described easily enough - psychologists use terms such as explicit/implicit, procedural/declarative or automatic/controlled to distinguish between the thought process. Explicit, declarative - or conscious - thoughts are those that can easily be expressed in words, for example, whereas subconscious ones are hard to articulate. Conscious thought processes are disrupted if you are forced to direct your attention elsewhere. Subconscious ones are not. But as yet you cannot simply look at an image of the brain and say what kind of thought process is being used.
Yet there are several ways to investigate the conscious/subconscious divide, as Stanislas Dehaene, director of the Cognitive Neuroimaging Unit at INSERM, the French equivalent of the US National Institutes of Health, points out. One is to study people with brain damage who have conditions such as blindsight - where they are unable to see visual stimuli on one side following an injury or stroke. While they may be unaware of seeing an action or an object, if forced to guess what was in that visual field they perform far better than would be expected by chance. This suggests that while they may not consciously see a stimulus, they are able to subconsciously process what they have seen and respond appropriately.
Another approach, which Dehaene uses in his lab, is called masking. Here volunteers are shown a word for just a few tens of milliseconds, followed by another image, the mask, which prevents the subject consciously noticing the word. By gradually increasing the delay between the word and mask, awareness of the word moves from the subconscious into the conscious mind. You can measure when this happens by asking subjects to say when they first notice the flashed word or, more objectively, by asking the volunteers questions about the target word - for example, asking them to decide whether it is a natural or artificial item. Using brain scans you can also look for differences in brain activity during subconscious and conscious perceptions of the word (PLoS Biology, vol 5, e260).
These methods show the masked word "popping" into consciousness when the interval between the two images is around 50 milliseconds - less if the word has emotional significance, which makes it more attention-grabbing. Dehaene's neuroimaging experiments, using both functional MRI and EEG, seem to reflect this, revealing widespread brain activity once the word is consciously perceived. He believes that two things are required for conscious processing: the stimulus has to be strong enough, and we have to focus our attention on it. Once this happens many areas of the brain, including working memory, have access to the word.
Sit up and take notice
So much for conscious perception. What does work like this tell us about the other side of the coin? Dehaene's masking experiments suggest that the subconscious is far from being a closed box. He has found that even when a word flashes up for less than 50 milliseconds and people are not aware of having seen it, they could still guess whether the word described a natural or artificial item more often than by chance.
What this suggests is that our brains constantly monitor our internal and external environment such that when the input becomes important enough, the subconscious decides to engage the conscious and we become aware of what is there. This is certainly what neurobiologist Michael Shadlen from the University of Washington in Seattle believes. "We suspect that the normal unconscious brain monitors the environment for cues that prompt it to decide whether to awaken and engage... The decision to engage at all is, in effect, an unconscious decision to be conscious."
This idea that consciousness is orchestrated by the subconscious brain finds support in the recent dramatic "awakening" of a man who had spent six years in a minimally conscious state. Nicholas Schiff of the Weill Cornell Medical College in New York and his team stimulated a part of the man's brain called the thalamus, which lies between the brainstem and the cerebral hemispheres and forms connections to the cortex. A special class of neurons within the thalamus, the calbindin-positive cells, have long been thought to play a role in arousal by stimulating the cortex. Sure enough, following stimulation of the thalamus, the man was suddenly able to open his eyes, speak and feed himself. In a commentary on the work, Shadlen and his colleague Roozbeh Kiani argue that this is the network through which the subconscious brain makes its decision to generate consciousness.
Crucially, Shadlen sees the subconscious and conscious as two parts of the same system, rather than two separate thought processors working in the same machine. However, while Shadlen argues for a unified model of mental processing, others want to further subdivide conscious and subconscious thought and have come up with alternative descriptions to replace the old two-part model. Peter Dayan, a theoretical neuroscientist at University College London, and colleagues Nathaniel Daw and Yael Niv, see the mind as comprising four systems that work together to control our decision-making and behaviour. First is the Pavlovian controller - the brain's autopilot, programmed by evolution to perform routine and instinctive behaviours such as fleeing from danger. Working primarily at the subconscious level, the Pavlovian controller is fast and efficient, if inflexible.
The other three control systems combine both conscious and subconscious thought to achieve the best possible outcome depending on the level of uncertainty about the situation you are in. The goal-directed controller corresponds most closely to popular notions of "rational thought". It allows you to optimise your choices by evaluating all the available information. When information is scarce, however - in unfamiliar situations or the very early stages of learning - another system, the episodic controller, takes charge. Instead of making complex calculations, it simply recommends adopting behaviours that have proved successful in similar situations in the past. Both rely heavily on conscious reasoning, and require you to focus on the problem at hand.
Once you achieve expertise in a skill such as driving, typing or playing golf, the fourth system, the habitual controller, comes into its own. Although we consciously learn to do these things, with experience they become second nature and we can do them automatically - in fact, once this happens, conscious analysis actually inhibits performance.
In this model, subconscious/implicit thought processes and conscious/explicit ones are more like equal partners than competitors. The two work together in the goal-directed controller, for example, to evaluate all the available information whether consciously or subconsciously perceived. So, for example, your decision to buy a certain product may be influenced by both explicit factors such as price and quality and implicit ones such as your mood, or an advert that you have seen but not necessarily noticed.
Dayan says that our behaviour is often driven by more than one of the four controllers - the various types of explicit and implicit thought process may be actively integrated, and this is especially true when we are learning something new where the balance between ignorance and experience changes. Importantly, the subconscious isn't the dumb cousin of the conscious, but rather a cousin with different skills.
What's more, non-conscious thinking may actually work best in some cases where you might imagine rational, conscious thought is the best tool for the job. In situations where people have to make difficult choices based on large amounts of hard-to-assess information, psychologist Ap Dijksterhuis at the University of Amsterdam in the Netherlands has found that they are happier with their decision when acting on gut instinct than when forced to try to think the choice through rationally (New Scientist, 5 May 2007, p 35). Dijksterhuis is convinced that subconscious thought processes are superior in many situations - including most social interactions - because they allow us to integrate complex information in a more holistic way than can be managed by rational thought processes.
Something similar sometimes happens in problem solving, according to Jonathan Schooler from the University of British Columbia in Vancouver. By asking subjects to explain their reasoning as they go, he has found that verbalising what they are doing has no effect on people's ability to solve analytical, mathematical or logic problems but actually hinders performance on insight problems, such as solving a riddle - those for which the solution seems to pop out of the blue in an aha! moment. Remember that subconscious thought processes differ from conscious ones in that we are unable to articulate the former. So here, it seems, is experimental evidence for something we all instinctively know: that subconscious thinking is the source of our inspiration - it is central to creativity.
A classic study into the neural basis of creativity suggests that it depends on an ability to shift gear between subconscious and conscious processing. Three decades ago, Colin Martindale of the University of Maine in Orono charted what is happening in the creative mind using EEG. He asked people to invent stories and found two distinct stages of brain activity. During the initial "inspiration" stage, their brains were remarkably quiet. Any activity was dominated by alpha waves, which indicates very low cortical arousal as though the conscious mind was quiescent while the subconscious worked behind the scenes. Intriguingly, you find a similar pattern during dream sleep and relaxation, two mental states also associated with high creativity. This "inspiration" stage was followed by a second stage, "elaboration", characterised by far more activity especially in the cortex, and probably associated with the conscious analysis and evaluation of ideas. People with the greatest difference in brain activity between these two stages were the most creative. More recently, Jordan Peterson at the University of Toronto, Canada, has argued that in highly creative people subconscious information is more likely to overspill into consciousness, giving them richer mental resources from which to make creative connections.
The sort of inspiration that comes in a flash is not just about creativity, however. Elke Weber from Columbia University, New York, points out that it is important for memory too. For example, when we are having difficulty remembering someone's name we often consign the problem to our subconscious in the knowledge that it will probably pop into our minds when we are no longer actively thinking about it. How this works is a mystery but, Weber argues, it surely belies the idea of the subconscious mind as inflexible and constrained.
So does all of this mean that the subconscious is as important an aspect of our humanity as the conscious mind? Ours is a species distinguished by its superior ability to learn new tricks, so maybe the subconscious - perhaps in the form of the habitual controller - took a crucial role in the evolution of our ancestors from bipedal apes to highly skilled tool-makers, hunters and craftspeople. Studies on rats and monkeys indicate that they too consign skills to subconscious control once they become expert. "Still, we may have a greater capacity for this," says Dayan, "since we have the huge advantage of being able to use language to boost our goal-directed control and so provide a much richer substrate for acquiring habitual skills."
The subconscious mind may even have a hand in our unique talent for language. Often we are only consciously aware of words as we speak them. So does that make language the mouthpiece of the non-conscious mind? And what about the process of learning to speak? Infants do not need tutoring to acquire their native language; they pick it up subconsciously. What's more they do this with remarkably little linguistic data - what the Harvard University linguist Noam Chomsky has called the "poverty of stimulus" - suggesting that this subconscious learning allows youngsters to use information very efficiently. Perhaps this also explains why new languages are more difficult to acquire after about the age of 8 - if we then gradually lose that subconscious ability and so have to learn language in a more formal, didactic and conscious way. These questions remain unanswered, and perhaps that is not surprising. As Dayan points out, we still have a long way to go before we fully understand the various components of subconscious thought. "The aspects of learning that lead us to acquire a language may have nothing whatsoever in common with other non-conscious facets," he says.
It is intriguing to wonder whether the human subconscious mind is different from that of other animals. Is there a human "higher subconscious" on a par with our "higher consciousness"? Given the difficulties of even pinning down the nature of consciousness, it is far too early to start elevating the subconscious to such heights. Still, if there is one thing everyone in Frankfurt agreed on, it is that our non-conscious thought processes are a lot cleverer than we once realised.