杏吧原创

TO UNDERSTAND consciousness, we need to know why it exists in the first place. New experimental evidence suggests it may have evolved to help us learn and adapt to changing circumstances far more rapidly and effectively.

We used to think consciousness was a uniquely human trait, but neuroscientists now believe we share it with many other animals, including birds and octopuses. While plants and arguably certain animals like jellyfish seem able to respond to the world around them without conscious awareness, many other animals consciously experience and perceive their environment.

In the 19th century, Thomas Henry Huxley and others argued that such consciousness is an 鈥渆piphenomenon鈥� 鈥� a mere side effect of the brain鈥檚 workings. More recently, it has been suggested that consciousness lets us synthesise external information so that, for example, we experience the sight and sound of a passing car as a unified perception, even though light and sound travel at different speeds.

Unconscious action

But ever more experiments are revealing that a surprising number of behaviours don鈥檛 need conscious attention, says at the School of Advanced Study, University of London. Once you have learned to ride a bicycle, you can do it without being consciously aware of cycling in the same way as you had to be when learning. Studies have also shown that you don鈥檛 need to be aware of a 鈥渟top鈥� sign to comply 鈥� can be enough to halt an action.

To see what differences there might be between conscious and unconscious perception, Travers and colleagues have been testing how well we learn when given wrong or misleading cues.

In the first experiment, volunteers gazed at a plus sign that appeared at the centre of a computer screen. About three-quarters of a second later, the sign was replaced by an arrow pointing left or right. The arrow lingered either for 33 milliseconds, so it could only be perceived unconsciously, or for 400 milliseconds, so that it entered conscious awareness. Finally, an X appeared to one side and the volunteers pressed a button to indicate whether it was on the left or right side of the screen.

Each volunteer sat through 200 trials with conscious arrow cues and 200 with subliminal ones. Each of these was further split into 100 rounds in which the cues pointed mostly in the correct direction, and 100 in which they were mostly wrong.

The team found that 聽when subliminal cues were largely incorrect, the participants were slower at pressing the correct button. But when cues reached conscious awareness, the participants learned when to disregard the misleading cues and responded faster.

In a second experiment, the team varied the percentage of times that both conscious and unconscious cues were incorrect, and tracked participants鈥� eye movements to see how this affected their speed at homing in on the target.

鈥淭he capacity for rapid, effective learning would almost certainly have been selected for by evolution鈥�

When the cue was unconscious, the participants took longer to push the button because they couldn鈥檛 help but look in the direction of the arrow, even when it was wrong 50聽per cent of the time. Because they were unable to adapt to the situation, they then had to find the target鈥檚 real location each time (PsyArXiv, ). 鈥淐onsciousness facilitates rapidly adjusting your behaviour in response to changes in the world,鈥� says Travers.

鈥淭his is brilliant research,鈥� says at the University of Mainz in Germany. 鈥淭he capacity for rapid, effective learning would almost certainly be something that evolution would have selected and maintained.鈥�

The study suggests that this capacity requires conscious awareness. This gives researchers a clue to a theory of consciousness in which it really does have a causal effect, says Metzinger.

This article appeared in print under the headline 鈥淭he point of consciousness鈥�