Three-year-old Grayson Clamp hears his dad’s voice for the first time

A three-year-old deaf boy from North Carolina boy is the first U.S. child to receive a cutting-edge hearing aid, which resulted in him hearing his father's voice for the first time a few weeks ago.

Caught on video, you can see Grayson's facial reactions light up as he familiarizes himself with sound. At first he seems delighted, but then seems perhaps overwhelmed by all the voices, He quickly shifs his sight and attention between his mother and father, as if in shock that he can hear both who are sitting on either side of him.

After his fosters parents, Len and Nicole Clamp, tried a cochlear implant without success, they turned to an auditory brain stem implant, which has only been used in adults before.

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"It was the most amazing thing I've ever seen," Len tells CNN. "No words to describe how excited we were, how validated we were, for all of the challenges."

Grayson was able to try the new type of hearing implant, used mostly in Europe up to this point, due to a Food and Drug Administration-approved trial for ten children.

He is missing the cochlear nerves in his ear to help him process and hear sound, and while his implant is working, it still needs some fine-tuning.

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"He's sound aware, but we don't know what exactly he hears," Grayson's surgeon Dr. Craig Buchman tells CNN.

The implant is powered by a battery outside his body.

Grayson is not the only little boy who has heard his parents voice for the first time in recent years due to specialized hearing aids.

Last July, we reported on a two-year-old Pennsylvania boy who heard is mother's voice for the first time due to a successful cochlear implant, the kind that did not work on Grayson.