Here's a powerful moment: at around the 2:12 mark of the video above, a three-year-old boy hears his father's voice for the first time.
Grayson Clamp of Charlotte, NC was born without hearing nerves in either ear, leaving him deaf since birth.
But the three-year-old recently received an auditory brain stem implant, allowing him to hear. He's the first child in the U.S. to have the procedure, CNN reports.
"I've never seen a look like that today," Len Clamp, Grayson's dad, said about the moment after the device was turned on. "He looked deep into my eyes, and he was hearing my voice for the first time. It was phenomenal."
Len and Nicole Clamp are Grayson's foster parents - they adopted him when he was a newborn.
When they heard about a Food and Drug Administration-approved trial of the auditory brain stem implant procedure for kids at the UNC Hospitals in Chapel Hill, North Carolina, they knew they wanted Grayson to have the procedure.
The device uses an external speech processor that listens to sounds, breaks them into their frequency components, and sends that information to an implanted device where his cochlear nerve would be if he had one.
Electrodes on Grayson's brain's cochlear nucleus are stimulated by the device, sending signals based on external sounds.
Doctors don't know exactly what he hears, but they hope his brain will learn to process sounds effectively over time.
For now, he is discovering lots of knew things: he loves the radio, his dad says, and often turns it on himself.
"It was the most amazing thing I've ever seen," Len Clamp said. "He's got a long way to go, but he's going to get there."