In Dreaming in Chinese, Deborah Fallows chronicles her adventures (and misadventures) stemming from a full-bath immersion in Chinese during a three-year sojourn. Memorizing and reproducing tones is indeed central to her struggles -- and her account sheds some light on the mystery of how tones can function so centrally.
One very funny tale involves her attempt to ask attentive attendants in a Chinese Taco Bell whether they offer take-out. To prepare us, Fallows explains that the each of the two syllables by which she tried to signify "take-out" could have at least four meanings, depending on tone. Possible meanings for one syllable include bag or parcel, eaten your fill, 'hail' as in rain pellets, newspaper and hug.. She cannot make herself understood. The restaurant greeter calls for reinforcements within, and she is surrounded by boys in sombreros struggling to decode her two syllables. The scene reminds me of Woody Allen attempting to rob a bank in Take the Money and Run, insisting to a crowd of helpful bank personnel that the last word of his scrawled note does indeed spell "gun".
Fallows is mystified as to why this is a such a struggle: "I'm thinking: 'C'mon, guy! Work with me here! How hard can this be?'" I had the same thought. But clarity comes for Fallows after many classroom struggles with tone. At chapter's end she explains:
Interesting but still abstract. So, back to the Taco Bell struggle:
The best time to approach tones, of course, would be at birth. Ah, to be born Chinese and have all this come naturally. But with the good news of effortless tone mastery comes a bit of bad news: Chinese speakers have a hard time not hearing tones. That is, for Chinese speakers, tones are so integral that they can't separate sounds of the word form the tone of the word (58).
Eureka. We Indo-European speakers instantly differentiate between words that vary by a consonant, including a hard-to-distinguish consonant within a blend, such as cr- vs. cl- above. Such capacity very early becomes unconscious, and once it becomes unconscious, we don't associate the two similar-sounding words (unless we're trying to rhyme, at which point their aural overlap strikes us as a glorious coincidence). Differentiating tones -- and failing to associate homonyms that vary only tone -- is no more remarkable than differentiating by consonant. As Fallows points out early, Chinese need the tone differentiating, since the language only has about 1/10 the syllables (as defined our western, vowel-consonant way) as English (I guess because they don't differentiate consonants as sharply as we do?).
For example, if a foreigner doesn't pronounce the tone correctly (like me with dabao), a typical Chinese person (boy in sombrero) would have a hard time making the leap to imagine what in the world the foreigner was trying to say. It just wouldn't occur to him that someone might be saying the word "takeout" when he was hearing the word "hug." Any more than it would occur to an English speaker that a foreigner might be saying, "I was out in Beijing, and I saw no crowds anywhere!" when he was actually saying, "I was out in Beijing, and I saw no clouds anywhere!" (58-59).
Questions for the linguists: why the different modes of differentiating words? Is it an accident of development, an outgrowth of morphology, culture, geography? Do different ways of differentiating sounds cause or lead to different ways of constructing reality? Are these differences related somehow to the different methods of writing -- characters vs. alphabet? I always wonder the same thing about accent and dialect -- at least when the dialogues split off indigenously, as opposed to being formed by new groups coming in. Why would separation by a mountain ridge or political border cause the particular sound changes that occur on either side? I imagine the answers are multiple, contingent, perhaps arbitrary -- the imprint, say, of one strong, idiosyncratic personality spreading within a region -- and mostly irrecoverable.
I suppose too that at least some linguists spend a lot of time on such questions, and I am --obviously -- gloriously ignorant of their findings.