#228: Perception as a Controlled Hallucination

May 28, 2018

Your World Is Just A Guess

This is a key lesson of our current understanding of the brain.  Using information we gather from our senses, along with inferences based on what we’ve experienced before, we experience a reality that is related to — but never a perfect match for — the real reality out there.

When we’re in familiar situations, under conditions our bodies are designed for, then the mapping between external reality and our internalized experience is pretty good.

But when something “looks impossible” — a movie’s special effect, or an optical illusion, or an athlete performing a feat that seems to defy the laws of physics — we glimpse the fact that we’re constructing our reality as we go along.  (Optical illusions are to your visual system what “auto-correct” is to typos on your smart phone.  It’s your brain’s on-the-fly attempt to make something sensible out of a confusing input stream.)

Before we’re even old enough to be laying down lasting memories, our brains are figuring out how to turn the bright, noisy mass of data from the outside world into a consistent and meaningful model of the world — one that we can make predictions based on.

An Oldie-but-Goodie

You’ve no doubt done the “blind spot” experiment, where you can prove to yourself that your brain “paints in” visual information where your optic nerve bungles the smoothness of your retina.  And if not, what the heck was wrong with your elementary school teacher for not showing you this?

As our brains recognize patterns, they look for patterns.  They find more patterns, and these become self-reinforcing.  This is an extremely efficient way to process the busy world around us — but it’s not always perfect, or perfectly accurate.

Resetting the dials on Reality

Dr. Anil Seth studies consciousness and perception at the University of Sussex, where he is a professor of Cognitive and Computational Neuroscience and Co­-Director of the Sackler Centre for Consciousness Science.  Among other studies into the malleability of perception, he has been able to experimentally induce synesthesia in non-synesthetic subjects.  😮

Synesthesia is a muddying-of-the-waters between what are normally separate senses; sounds evoking the perception of colors, text characters evoking tactile sensations, etc.

This induced synesthesia isn’t a permanent change — probably a good thing — but it does show the incredible plasticity of the human brain, even in adults.  And it highlights the non-objective nature of perceptual experience.  (Get ready to have less faith in courtroom witness testimony after you hear this conversation.)

In Episode #228, Dr. Seth explains the relevance of hallucinations to everyday perception, how meditation might be used to better train our attention, and how “Bayesian priors” can influence our experience of the world.  And not surprisingly, psychedelic drugs come up too.  And octopuses.  🙂


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The world’s leading scientists from a variety of domains – and more than a couple non-scientists with an encyclopedic knowledge of aliens in pop culture – discuss the latest thinking on the Big Question: “Are we alone in the universe?”

Show Notes
  • 00:00:37

    Episode introduction: Perception as a Controlled Hallucination.

  • 00:02:37

    This Week In Neuroscience: Olfactory neurons, freeze behavior, and breathing rate.

  • 00:05:10

    5-Star review shoutouts.

  • 00:05:49

    SDS news and updates.

  • 00:06:57

    Guest introduction: Dr. Anil Seth.

  • 00:08:13

    Interview begins.

  • 00:09:48

    Perception of color.

  • 00:10:31

    Is the dress blue and black or white and gold?

  • 00:11:38

    Understanding perceptual hallucinations.

  • 00:12:48

    Gain control and the process of balancing signal to noise.

  • 00:14:13

    Quantitatively measuring the ways in which people use attention to drive their perceptions.

  • 00:16:33

    Training attention.

  • 00:19:35

    Using cognitive training methods to change conscious perceptions.

  • 00:20:00

    Synesthesia, perception, and cultural constructs.

  • 00:28:58

    Psychedelics and visual hallucinations.

  • 00:30:12

    Research on neural complexity.

  • 00:33:15

    Current and future research aims.

  • 00:34:50

    The role of arousal and complexity in perception.

  • 00:36:09

    Interoceptive sensitivity.

  • 00:40:13

    Interview wrap-up.

  • 00:41:18

    Ruthless Listener Retention Gimmick: What do dogs visualize?

  • 00:43:16

    Episode wrap-up.

One comment

  1. don salmon says:

    If everything we perceive is a hallucination created by the brain, why isn’t the percept “brain” also a hallucination?

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