Introducing the brain: predicting perception (Introduction)

by David Turell , Monday, November 15, 2021, 17:23 (894 days ago) @ David Turell

A new theory of how the brain works:

https://www.quantamagazine.org/to-be-energy-efficient-brains-predict-their-perceptions-...

"How our brain, a three-pound mass of tissue encased within a bony skull, creates perceptions from sensations is a long-standing mystery. Abundant evidence and decades of sustained research suggest that the brain cannot simply be assembling sensory information, as though it were putting together a jigsaw puzzle, to perceive its surroundings. This is borne out by the fact that the brain can construct a scene based on the light entering our eyes, even when the incoming information is noisy and ambiguous.

"Consequently, many neuroscientists are pivoting to a view of the brain as a “prediction machine.” Through predictive processing, the brain uses its prior knowledge of the world to make inferences or generate hypotheses about the causes of incoming sensory information. Those hypotheses — and not the sensory inputs themselves — give rise to perceptions in our mind’s eye. The more ambiguous the input, the greater the reliance on prior knowledge.

“'The beauty of the predictive processing framework [is] that it has a really large — sometimes critics might say too large — capacity to explain a lot of different phenomena in many different systems,” said Floris de Lange, a neuroscientist at the Predictive Brain Lab of Radboud University in the Netherlands.

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[I've skipped a long recitation of computer studies.]

"Persuasive as these insights from computational studies may seem, in the end, only evidence from live brains can convince neuroscientists of predictive processing in the brain. To this end, Blake Richards, a neuroscientist and computer scientist at McGill University and Mila, the Quebec Artificial Intelligence Institute, and his colleagues formulated some clear hypotheses about what they should see in brains learning to make predictions about unexpected events.

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"Of particular interest were certain pyramidal neurons in the brain’s neocortex, which are thought to be anatomically suited to predictive processing. They can receive both local bottom-up sensory signals from nearby neurons (through inputs to their cell body) and top-down prediction signals from more distant neurons (through their apical dendrites).

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"All the while, the researchers observed the activity in the mice’s brains.

"What they saw was that lots of neurons responded differently to expected and unexpected stimuli. Crucially, this difference was strong in the local, bottom-up signals on the first day of testing, but it waned on the second and third days. In the context of predictive processing, this suggested that newly formed top-down expectations began inhibiting the responses to incoming sensory information as the stimuli became less surprising.

"Meanwhile, the opposite was happening in the apical dendrites: The difference in their response to unexpected stimuli increased over time. The neural circuits appeared to be learning to represent properties of the surprising events better, to make better predictions the next time around.

“'This study provides further support for the idea that something like predictive learning or predictive coding is happening in the neocortex,” said Richards.

"It’s true that individual observations of neuronal activity or an animal’s behavior can at times be explained by some other model of the brain. For example, the waning responses in neurons to the same input, instead of being interpreted as the inhibition of error units, might simply be due to a process of adaptation. But then “you get this whole phone book of explanations for different phenomena,” said de Lange.

"Predictive processing, on the other hand, provides a unifying framework to explain many phenomena in one go, hence its allure as a theory of how the brain works. “I think the evidence at this point is pretty compelling,” said Richards. “I’m willing to put a lot of money on that claim, actually.'”

Comment: all along in the past I have predicted the brain is built to help us perceive. It makes perfect sense to view it that way.