In 1975, a man sustained a terrible injury to his brain that left him, among other things, unable to distinguish tastes. He couldn't tell sugar water from salt water. In 2005, one experiment caused him to strongly prefer sugar to salt. Here's the tweak that changed things.
Patient B has spent much of the last thirty years under medical care. In 1975, brain inflammation put him in a coma, and when he woke up he couldn't store any new information. He could only hold on to information for about forty seconds at a time. Neuroscientists were eager to experiment on him - with the proper ethics board supervision of course - and not just because of the amnesia.
A damaged amygdala left Patient B with no ability to register disgust. He couldn't even fathom the feeling. When asked about a story about a character who threw up, he believed the character felt hungry. He felt no disgust at the distasteful food he was served. He wasn't even able to distinguish between a small cup of salt water and sugar water.
Thirty years after his injury, researchers gave him the sugar and salt water test again, except they colored the water red and green. The colors didn't correspond to the contents of the water. Sometimes the sugar water was red, and sometimes it was green. No matter what color it was, Patient B suddenly insisted on only drinking the sugar water. He sometimes refused to drink the salt water at all, and this was a guy who pronounced everything he ate or drank delicious.
B was not aware of the sweetness. He didn't taste anything, consciously. All the same he "tasted" the sugar water and the salt water. The researchers think that, somehow, he must have tasted it all along, without being consciously aware of it. The colors for some reason gave the portion of his brain that actually tasted the substances a line of communication to his conscious mind. The line of communication was primitive - this color water good, that color water bad - but it did allow him to consciously "taste," even though it should have done nothing of the kind.
Image: Evan Amos
[Source: Tasty: The Art and Science of What We Eat.]