How Your Thoughts Are Built & How You Can Shape Them | Dr. Jennifer Groh
Timestamps are as accurate as they can be but may be slightly off. We encourage you to listen to the full context.
Podcast Summary
This episode explores how our brains integrate different senses to perceive and navigate the world with Dr. Jennifer Groh, a professor of psychology and neuroscience at Duke University. The conversation delves into how sight and sound merge in the brain, what thoughts actually are at a neural level, and how sensory integration affects focus and attention. (00:00) Dr. Groh explains the fascinating discovery that eye movements influence how we process sound, revealing that the brain creates dynamic maps that constantly update based on where we're looking. (03:41)
- Main Theme: The episode focuses on multisensory integration - specifically how vision and hearing work together - and introduces a compelling theory about what thoughts actually are in terms of brain simulation and sensory processing.
Speakers
Dr. Jennifer Groh
Dr. Jennifer Groh is a professor of psychology and neuroscience at Duke University who studies how our brain represents the world around us through sensory integration. Her laboratory focuses particularly on how different senses merge in the brain to help us focus and learn more effectively, including groundbreaking research on how eye movements control what our brain is capable of processing. She is also an accomplished musician who plays banjo and sings, and raises bantam chickens in Chapel Hill, North Carolina.
Andrew Huberman
Andrew Huberman is a professor of neurobiology and ophthalmology at Stanford School of Medicine and host of the Huberman Lab Podcast. He has been in neuroscience for nearly three decades and brings expertise in vision science and neural circuits to explore how sensory systems shape our experience and cognitive abilities.
Key Takeaways
Sound Localization Requires Incredibly Precise Timing
Our ability to locate sounds depends on detecting timing differences between our ears of just half a millisecond - less than the duration of a single brain cell's electrical signal. (15:28) This remarkable feat occurs because sound from the right reaches your right ear before your left ear, and your brain uses these tiny delays to calculate direction. Dr. Groh explains this system must be learned and continuously updated as children grow, since a baby's head is about half the width of an adult's head, changing the timing relationships. This precision explains why people with hearing loss in one ear struggle with sound localization and why the folds in our ears create unique acoustic fingerprints for each individual.
Your Brain Controls Your Ears During Eye Movements
Every time you move your eyes, your brain sends signals to muscles in your ears, causing your eardrums to move in precise patterns. (67:30) Dr. Groh's research discovered that when eyes move left, the right eardrum bulges inward then outward, while the left ear does the opposite, creating a wave-like pattern. This finding suggests that the integration of vision and hearing begins much earlier in the sensory processing chain than previously thought - possibly at the level of the ear itself rather than just in higher brain regions. This mechanism may be the first step in helping us locate sounds relative to where we're looking.
Thoughts Are Sensory Simulations in Your Brain
When you think about something, your brain runs mini-simulations using the same sensory areas involved in actually perceiving that thing. (88:47) Dr. Groh explains that thinking about a cat activates visual cortex (what it looks like), auditory cortex (what it sounds like), and even olfactory regions (how it smells). This theory explains why trying to have a conversation while navigating difficult traffic is challenging - both tasks compete for the same cognitive resources. It also suggests that humans' expanded sensory brain areas compared to other primates may be used for generating these internal simulations, which could be the biological basis of our enhanced thinking abilities.
Focus Requires Interval Training Like Physical Exercise
Deep cognitive work operates similarly to physical exercise, requiring intervals of intense effort followed by recovery periods. (102:22) Dr. Groh describes her writing process as being able to produce one effortful sentence, then needing a break before the next one - like a sprinter who can run at maximum effort for short bursts. She emphasizes trusting this natural rhythm rather than fighting it, allowing ideas to "marinate" during rest periods. This approach acknowledges that attention is a limited resource that can be depleted and needs recovery, similar to how muscles work. The key is creating systems that work with these natural cycles rather than forcing continuous focus.
Your Physical Environment Actively Shapes Your Brain State
The spaces we occupy fundamentally influence our cognitive abilities and attention through sensory cues and environmental constraints. (77:00) Dr. Groh demonstrates this with examples like Grand Central Station's whispering gallery, where architectural features allow whispers to travel 25 feet, and how cathedral acoustics influenced the development of slower, more sustained musical forms like Gregorian chant. She advocates for changing physical locations when stuck on cognitive tasks, as new environments can shift you out of mental ruts. This principle extends to creating dedicated work spaces with controlled sensory inputs, like her basement office with no internet access, to support sustained focus.
Statistics & Facts
- The maximum timing difference between sound arriving at your two ears is only half a millisecond - even for sounds coming from directly to your left versus directly to your right. (15:28) Dr. Groh explains this is remarkably precise considering it's less than the duration of a single neural action potential.
- If you live long enough, 80% of people will develop hearing loss at some point in their lives. (28:23) Dr. Groh notes this is becoming a bigger problem as young people accumulate more sound exposure through constant earbud use.
- Six percent of the population is red-green colorblind, which operationally means they cannot distinguish between red and green colors, though they can still see both. (42:22) Dr. Groh uses this as an example of how warning systems need to account for sensory limitations in the population.
