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Alfred Anwander, MPI-CBS
The debate over how consciousness is processed is unresolved.
OPEN MINDED

A “time slice” theory of consciousness suggests we’re not continually aware of our surroundings

By Olivia Goldhill

How do you perceive your own consciousness?

If this is the first time you’ve considered such a question, it’s likely you consider it to be smooth and continuous, registering movements and changes as events happen in the world around you. You most likely consider yourself conscious all the time, unless you’re asleep or knocked out. 

But for those who study the mind, including philosophers, psychologists and neuroscientists, this notion of consciousness is far from obvious. While intuitively, we may believe that consciousness is a continual flow, there’s considerable evidence to suggest that our conscious perception comes in discrete snapshots, like distinct images flicking quickly through a film reel. A paper published in PloS Biology this month has put forward a theory in an attempt to reconcile these theories of consciousness, arguing that consciousness is in fact developed in two stages.

First, the authors argue, we unconsciously process visual stimuli continuously, and are oblivious to this stage. We only then become consciously aware of the information once it has been transferred to conscious perception, which happens in discrete moments, or “time slices.”

Michael Herzog, a professor at the École polytechnique fédérale de Lausanne’s Brain Mind Institute in Switzerland, and Frank Scharnowski, a cognitive neuroscientist at the University of Zurich, argue that we’re unaware of the gaps in our consciousness. They say there can be a 400-milisecond lag between unconsciously receiving stimuli and transferring it to conscious perception.

“We perceive time as continuous just as we perceive a line as continuous even though its ink is of discrete atomic nature,” the authors write in their paper.

But our perception of conscious does not align with reality. “According to our model, the output of unconscious processing is discrete, meaningful, and rendered conscious at once. Large parts of unconscious processing will never reach consciousness,” the researchers say.

The authors note that the debate over how consciousness works has a long history. In the third century BC, the Abhidharma Buddhist school put forward the theory that consciousness is made up of discrete moments. There are numerous more recent papers arguing for just such a conclusion. Meanwhile, experiments show that when two stimuli are presented in rapid succession, they’re perceived simultaneously, while discrete perception is thought to explain various visual tricks, such as the optical illusion that often makes spoked wheels look as though they’re moving in reverse,  and flash lag illusion, where a flash that occurs in the same place as a moving object is perceived to be in a different location.

Herzog and Scharnowski argue that the evidence points to neither clear-cut continual nor snapshot theories of consciousness, but that their two-stage theory reconciles our sense of continual consciousness with the counter-evidence.

Axel Cleeremans from the Université Libre de Bruxelles, who was not involved in the study, tells Quartz that others have come to a similar conclusion.

Ultimately, Herzog and Scharnowski note in their paper that the debate over consciousness remains unresolved. Their theory may fit certain key characteristics of consciousness, but it doesn’t yet hold definitive answers.