Hearing and language

This question arise from tonal languages, ie, Thai, Laos, Mandarin, Cantonese, etc. In Thai, for example, there are five different tones. Depending on the tone the word can change drastically. The five tones in Thai language are normal/flat, low, falling, high and rising. It would seem logical that you could “fake” your way through these tones, but in my experience when I try to speak Thai, if I don’t get the tone correct then the listener gets totally perplexed.

I have hear of something called “tone deafness” and originally thought this was mostly used to denote someone who could not carry a tune, ie, “That Harry, he couldn’t carry a tune in a garbage pail. He is totally tone deaf.”
However a little research indicated this was partially true, but that there may also be people who cannot distinguish between hearing different tones, not just people who have trouble reproducing musical notes.

I also found another from Cervaise that asked related but different questions about tonal languages. But I didn’t really find the answers in that thread very satisfactory.

Now Mrs. ShibbOleth, who is a native Thai speaker (and makes derisive comments about my feeble attempt to reproduce Thai speech) is somewhat of the opinion that although we refer to Thai as a tonal language, that it is almost a difference of aspiration as much as tone. Maybe.

So my questions: [list=1][]Does true tone deafness exist? I suspect that there are varying degrees of ability to hear tones ranging from “perfect pitch” to “totally tone deaf”, and that most people fall somewhere in the middle of a bell shaped curve in their ability to both hear and reproduce sounds, but that is purely a hunch.[]Are the tones in a tonal language the same as what we refer to in the sense of tone deafness?[]Are there people who are considered deaf in their native country, who are merely tone deaf, which makes them incapable of communicating even though they can actually hear sounds?[]If the answer to the previous is yes, then how far along the scale would someone have to be before they were unable to communicate?Would there also be people who would be considered to have a speech impediment who were just unable to reproduce the sounds that they could here?