This reminds me a lot of https://en.wikipedia.org/wiki/Prosopagnosia https://en.wikipedia.org/wiki/Prosopagnosia also known as "face blindness". People with the

This reminds me a lot of https://en.wikipedia.org/wiki/Prosopagnosia https://en.wikipedia.org/wiki/Prosopagnosia also known as "face blindness". People with the disorder can see perfectly fine, but have trouble recognizing people's faces, just as your son hears just fine, but has trouble recognizing people's speech. Similarly, I know someone who beat brain cancer, but after a certain point he became unable to properly taste/enjoy food. Interestingly, these disorders all seem to have pretty direct neurological causes: there is something causing a difference in the person's brain between where they sense the information and where they process it, whether it's genetic (i.e. affecting the layout and growth of the brain) or due to trauma such as a head injury. I'm curious as to whether your son is able to enjoy music, especially music with multiple different instruments playing simultaneously. I have a theory that the same process on a neurological level that makes food pleasurable is what makes smells smell good, music sound good, certain surface (e.g. soft fur) feel good, and certain sights (e.g. a mountain stream) look good. I mean that not from a neurotransmitter perspective, but in the actual neural processing. It seems these configurations are programmed into our brains genetically, just as our propensity toward recognizing faces/speech are, which is fascinating.