What happens when we become aware of something, such as a faint sound or an object out of the corner of our eye? Did it pop all at once into our conscious awareness? Or was our awareness of it more gradual? And if so, why? Researchers studying the question can help us puzzle out some of the subtle workings of the brain and the nature of consciousness.
Now Axel Cleeremans (Center for Research in Cognition & Neurosciences, Université Libre de Bruxelles), a senior fellow in CIFAR’s Brain, Mind & Consciousness program, has new research that suggests that the transition from unconscious to conscious perception is gradual, and our experience of it has to do with how much cognitive processing power a task requires. The work has implications for our understanding of how and why consciousness itself arises.
Previous laboratory experiments in which people are asked to detect stimuli such as symbols flashing quickly past on a screen have suggested that conscious awareness is all or nothing. But Cleeremans says his intuition is that consciousness of a stimulus has to have intermediate steps as well.
“You can be paying attention to a conversation and you’re focused. But by the same token, you have a fringe awareness of what’s around you. You’re aware of distant sounds. It isn’t just that everything is black, and you’re just perceiving what you’re paying attention to,” he says.
In work with Dariusz Asanowicz of Jagiellonian University and other colleagues, Cleeremans designed a lab test that demonstrates this graded consciousness, and suggests that the extent to which your perception is graded vs. all-or-none depends partly on how much processing power a task takes up.
In the experiment, subjects looking at a computer screen were presented with pairs of letters that were shown very quickly, for anywhere between 16 and 128 milliseconds. In one experiment subjects were asked to tell if the letters were the same or different colours (a low-level task) or whether they were both consonants vs. vowels (a high-level task). In another, they were asked if the pairs were physically identical (a low-level task) or whether they were both consonants vs. vowels (a high-level task). Then they were asked to rate whether they had been conscious of the letters, using a qualitative scale designed by the Danish psychologist Morten Overgaard. The scale is called the Perceptual Awareness Scale and asks participants to judge their visual experience of the stimulus.
Similar experiments in the past have shown that people can often solve problems like these even when they are not aware they have seen anything. Show them a stimulus and ask them to “guess” at the correct answers, and they will still get them right, demonstrating that they were solving the problem without being conscious of it.
The recent experiment showed that when people have to expend a relatively high amount of processing power on a problem – in this case, deciding whether letters are both vowels or both consonants or not – they also tend to rate their awareness of seeing the letters as very high. But when they only have to decide colours, which requires less processing, they were much more likely to say that they were only partly aware of having seen the stimulus.
For Cleeremans, this tends to validate the “level of processing” hypothesis he proposed several years ago in another similar study with Bert Windey, which says that the complexity of a task influences whether it is perceived consciously or unconsciously. A task that involves high-level, abstract processing will force itself into our conscious awareness. One that takes little, low-level processing is more likely to result only in partial awareness.
Cleeremans thinks that the experiment is a stroke against one of the leading theories of conscious perception, called the global workspace hypothesis. This suggests that much of our cognitive processing occurs within cognitive modules that normally operate beneath our awareness. But a task that requires attention from a number of modules gets thrown into a global workspace – in effect, shining a spotlight on it and bringing it to conscious awareness. Cleeremans thinks this work makes the global workspace hypothesis less likely, since it shows that consciousness is not always all or nothing.