Consciousness Arises In Discrete Time Slices, Suggests Study

A new way of understanding of how the brain processes unconscious information into our consciousness has been proposed by researchers at Ecole Polytechnique Federale de Lausanne. According to the model, consciousness arises only in time intervals of up to 400 milliseconds, with gaps of unconsciousness in between.

A driver ahead suddenly stops, for example, and you find yourself stomping on your breaks before you even realize what is going on. We would call this a reflex, but the underlying reality is much more complex, forming a debate that goes back centuries.

Is consciousness a constant, uninterrupted stream or a series of discrete bits – like the 24 frames-per-second of a movie reel?

Consciousness appears to us as a continuous stream: one image or sound or smell or touch smoothly follows the other, providing us with a continuous image of the world around us. As far as we are concerned, it seems that sensory information is continuously translated into conscious perception.

Discrete vs. Continuous Consciousness

We see objects move smoothly, we hear sounds continuously, and we smell and feel without interruption. However, another school of thought argues that our brain collects sensory information only at discrete time-points, like a camera taking snapshots.

Even though there is a growing body of evidence against “continuous” consciousness, it also looks like that the “discrete” theory of snapshots is too simple to be true.

Michael Herzog at EPFL, working with Frank Scharnowski at the University of Zurich, have now developed a new paradigm, or “conceptual framework”, of how consciousness might actually work. They did this by reviewing data from previously published psychological and behavioral experiments that aim to determine if consciousness is continuous or discrete.

Such experiments can involve showing a person two images in rapid succession and asking them to distinguish between them while monitoring their brain activity.

Two-stage Model

The new model proposes a two-stage processing of information.

First comes the unconscious stage: The brain processes specific features of objects, e.g. color or shape, and analyzes them quasi-continuously and unconsciously with a very high time-resolution.

However, the model suggests that there is no perception of time during this unconscious processing. Even time features, such as duration or color change, are not perceived during this period.

Instead, the brain represents its duration as a kind of “number”, just as it does for color and shape.

Then comes the conscious stage: Unconscious processing is completed, and the brain simultaneously renders all the features conscious. This produces the final “picture”, which the brain finally presents to our consciousness, making us aware of the stimulus.

The whole process, from stimulus to conscious perception, can last up to 400 milliseconds, which is a considerable delay from a physiological point of view.

“The reason is that the brain wants to give you the best, clearest information it can, and this demands a substantial amount of time,” explains Michael Herzog. “There is no advantage in making you aware of its unconscious processing, because that would be immensely confusing.”

This model focuses on visual perception, but the time delay might be different for other sensory information, e.g. auditory or olfactory.

This is the first two-stage model of how consciousness arises, and it provides a more complete picture of how the brain manages consciousness than the “continuous versus discrete” debate envisages. But it especially provides useful insights about the way the brain processes time and relates it to our perception of the world.

17 Stage Model

There is an interesting parallel in an ancient philosophy. According to the Theravada Buddhist tradition, as written in the Abhidhamma Pitaka, the arising of thought from the mind occurs in 17 discrete steps.

The recent book Waking, Sleeping, Dreaming by philosopher Evan Thompson explores the relation between Buddhist ideas, neuroscience and cognitive science in depth. He too concludes that consciousness occurs as a series of discrete moments of awareness, but with the possibility of much finer resolution:

“As mentioned earlier, the Abhidharma measures that seem observational work out to around 10-20 millisenconds as the time it takes for a minimal amount of awareness to occur. This estimate might seem remarkable from the perspective of cognitive science. It’s significantly less that the 100-250 millisecond time periods usually given for a moment of reportable perceptual awareness..”

He then mentions a 2007 study by Remigiusz Szczepanowski and Luis Pessoa (J Vis. 2007 Mar 27;7(4):10.) in which some subjects were able to perceive a target stimulus presented for only 17 milliseconds. He continues:

“These findings suggest that being able to identify and describe discrete moments of awareness happening as fast as 10-20 milliseconds is by no means beyond the human mind, especially the mind trained in meditation.”

Abstract

We experience the world as a seamless stream of percepts. However, intriguing illusions and recent experiments suggest that the world is not continuously translated into conscious perception. Instead, perception seems to operate in a discrete manner, just like movies appear continuous although they consist of discrete images. To explain how the temporal resolution of human vision can be fast compared to sluggish conscious perception, we propose a novel conceptual framework in which features of objects, such as their color, are quasi-continuously and unconsciously analyzed with high temporal resolution. Like other features, temporal features, such as duration, are coded as quantitative labels. When unconscious processing is “completed,” all features are simultaneously rendered conscious at discrete moments in time, sometimes even hundreds of milliseconds after stimuli were presented.[/alert-announce]

Michael H. Herzog et al.
Time Slices: What Is the Duration of a Percept?
PLOS Biology (2016). DOI: 10.1371/journal.pbio.1002433

Image: Jean Livet and the 2007 Olympus BioScapes Digital Imaging Competition – (CC BY-NC-ND 3.0) Montage image of a brain stem from a Brainbow transgenic mouse. In Brainbow mice, neurons randomly choose combinations of red, yellow and cyan fluorescent proteins, so that they each glow a particular color. This provides a way to distinguish neighboring neurons and visualize brain circuits. These are large caliber axons of the auditory pathway.

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