To understand consciousness, researchers need to go beyond the idea that it can be measured on a single scale. Instead, they need to see it as having multiple dimensions.
The conclusion by two researchers in the Azrieli Program in Brain, Mind & Consciousness at CIFAR is published in Trends in Cognitive Sciences, and is the result of a discussion between philosophers and neuroscientists at the first meeting of the new program.
“It’s a nice point of contact between philosophers and neuroscientists,” says Tim Bayne (Western University), a philosopher and a CIFAR senior fellow in the program. “We’re trained to think about questions of taxonomy. Neuroscientists ground the discussion in the specifics of the science.”
Bayne published the paper along with CIFAR Senior Fellow and Program Co-Director Adrian Owen (also of Western), who is a neuroscientist, as well as their co-author Jakob Hohwy at Monash University in Melbourne). The idea first came up at a discussion during the first CIFAR program meeting, Bayne says.
Examples of the different ways consciousness could be measured along multiple dimensions that don’t track well with higher and lower levels.
Researchers and doctors use levels of consciousness to describe coma and its aftermath, with the level of consciousness increasing from coma to vegetative state to minimally conscious state and beyond. Levels are also increasingly used to describe consciousness in the context of light sedation, sleep and certain types of epileptic seizures.
The problem, say Bayne and Owen, is that consciousness isn’t that simple. It’s not like height or weight which can only increase or decrease.
For instance, how do you compare the level of consciousness of someone asleep and dreaming with someone who is sedated? Neither is aware of the outside world. But we know the dreamer is experiencing his dreams, whereas the sedated person likely isn’t. Is one more conscious than the other?
Instead, Bayne and Owen say that researchers need to work out a multi-dimensional scale of consciousness. They suggest at least two broad areas of measurement. The first would have to do with the contents of consciousness. For instance, a fully awake person is open to a wide variety of detailed contents, from seeing a bird in flight to recognizing a familiar face. A lightly sedated person, on the other hand, might have only vague awareness of motion, or the shape of a face.
The other dimension is functional. This has to do with how available the contents of consciousness are to reasoning, memory, executive action, etc. For instance, Owen’s work has shown that some people in an apparently vegetative state are actually aware of the outside world and able to engage in certain kinds of actions (such as imagining scenes) on command. People having certain kinds of epileptic seizures can react to their perceptions, but may not be able to reason or form memories based on those perceptions.
Bayne says that a better understanding of the different dimensions of consciousness will help researchers to understand how consciousness is grounded in the workings of the brain, and may also have implications for treating disorders of consciousness.