The Science of Sound
When sound waves reach the inner ear, neurons pick up the vibrations and alert the brain. Encoded in their signals is a wealth of information that enables us to follow conversations, recognize familiar voices, appreciate music, and quickly locate a ringing phone or crying baby.
How We Hear
Neurons send signals by emitting spikes – brief changes in voltage that propagate along nerve fibers, also known as action potentials. Remarkably, auditory neurons can fire hundreds of spikes per second, and time their spikes with exquisite precision to match the oscillations of incoming sound waves.
The Importance of Timing
With powerful new models of human hearing, scientists at MIT’s McGovern Institute for Brain Research have determined that this precise timing is vital for some of the most important ways we make sense of auditory information, including recognizing voices and localizing sounds.
The Open-Access Findings
The open-access findings, reported in the journal Nature Communications, show how machine learning can help neuroscientists understand how the brain uses auditory information in the real world. MIT professor and McGovern investigator Josh McDermott, who led the research, explains that his team’s models better-equip researchers to study the consequences of different types of hearing impairment and devise more effective interventions.
The Role of Artificial Neural Networks
Neuroscientists have long used computational models to explore how sensory information might be decoded by the brain, but until recent advances in computing power and machine learning methods, these models were limited to simulating simple tasks. "One of the problems with these prior models is that they’re often way too good," says Mark Saddler, a graduate student who worked with McDermott on the project. "For example, a computational model tasked with identifying the higher pitch in a pair of simple tones is likely to perform better than people who are asked to do the same thing. This is not the kind of task that we do every day in hearing. The brain is not optimized to solve this very artificial task."
The Breakthrough
To better understand the brain, Saddler and McDermott wanted to challenge a hearing model to do things that people use their hearing for in the real world, like recognizing words and voices. That meant developing an artificial neural network to simulate the parts of the brain that receive input from the ear. The network was given input from some 32,000 simulated sound-detecting sensory neurons and then optimized for various real-world tasks.
The Results
The researchers showed that their model replicated human hearing well – better than any previous model of auditory behavior. In one test, the artificial neural network was asked to recognize words and voices within dozens of types of background noise, from the hum of an airplane cabin to enthusiastic applause. Under every condition, the model performed very similarly to humans.
Conclusion
The team’s findings demonstrate how artificial neural networks can help neuroscientists understand how the information extracted by the ear influences our perception of the world, both when hearing is intact and when it is impaired. "The ability to link patterns of firing in the auditory nerve with behavior opens a lot of doors," McDermott says. "Now that we have these models that link neural responses in the ear to auditory behavior, we can ask, ‘If we simulate different types of hearing loss, what effect is that going to have on our auditory abilities?’"
FAQs
Q: What is the importance of timing in the auditory system?
A: Precise timing is vital for recognizing voices, localizing sounds, and understanding auditory information.
Q: How do neurons send signals?
A: Neurons send signals by emitting spikes – brief changes in voltage that propagate along nerve fibers, also known as action potentials.
Q: What is the role of artificial neural networks in understanding the brain?
A: Artificial neural networks can help neuroscientists understand how the brain uses auditory information in the real world and how it is influenced by hearing loss.
Q: What are the implications of these findings for hearing loss?
A: The team’s findings can help researchers better diagnose hearing loss and design more effective hearing aids and cochlear implants.
