Our conscious perception of the world feels like a continuous and uninterrupted flow, but a new study suggests that it's actually more like the frames of a movie reel running through a projector. There's still a lot we don't know about consciousness and how it arises in the brain. Even though perception -- such as vision and hearing -- feels smooth and uninterrupted, neuroscientists aren't entirely sure if it flows continuously like water through a tap or if it's more like the aforementioned 24-frame-per-second movie reel.
A team of European researchers now say it's more like the latter -- but with a twist. Their new conceptual framework, published in PLOS Biology, suggests that we initially process incoming sensory information in an unconscious state, which then shifts to full perceptual awareness. And it all happens in blips, or "time slices", lasting for as long as 400 millisecond intervals.
The two-stage model of visual perception. Image: Michael H. Herzog et al., 2016/PLOS Biology
The new model, developed by Michael Herzog from the Swiss Federal Institute of Technology in Lausanne (EPFL) and Frank Scharnowski from the University of Zurich, proposes a two-stage processing of sensory information. During the first phase, the brain processes specific features of an object, say, its colour or shape. This scanning is done semi-continuously, but we humans are completely unaware that it's happening. During this first phase, even changes to the object (like a change in its colour or brightness) aren't consciously perceived.
But then comes the second stage: the transference of the stimulus to actual conscious perception. During this stage, the brain renders the perceived features after the unconscious processing has been completed. We experience all this as qualia (that is, subjective) conscious experience arising from sense perception. It's like that moment when a polaroid film reveals its hidden details and we're finally aware of what we're looking at -- except this process happens so fast that we're oblivious to the "developing" phase.
"When unconscious processing is 'completed'," the researchers explained in the study, "all features are simultaneously rendered conscious at discrete moments in time, sometimes even hundreds of milliseconds after stimuli were presented."
That means there's a lag from when we first experience something, to when we're actually aware of it. (This might actually explain the flash-lag illusion.) This entire two-stage process, from start to finish, can last up to 400 milliseconds -- which is a long time from a psychological perspective.
"The reason is that the brain wants to give you the best, clearest information it can, and this demands a substantial amount of time," Herzog said in a statement. "There is no advantage in making you aware of its unconscious processing, because that would be immensely confusing."
Herzog and Scharnowski's model suggests we're not as conscious as we think we are. If they're right, it means we're unconscious for a significant portion of our waking life. But like the gaps between film slides, we're unaware of these "black outs".
The implication is that there's no such thing as a continuous and immutable self nor is there an ever-present soul. Instead, our brains are constantly churning out snapshots of perception, which to us feel real and consistent. Combined with other aspects of cognition (like memory), it gives rise to self-awareness and the impression that we live in a coherent universe.
This new model only considers visual processing. Something very different may be happening in the brain when it processes other information, such as sound, touch or smell. That said, the research offers a more complete picture of brain functioning than what's presented by advocates of the simplistic "continuous or discrete" view of human consciousness.