But there are implications to the fact that slides are built from very many hits, but not vice versa: that fact opens up the possibility of a fundamental event type that is not quite a hit, and not quite a slide. To understand this new event type, let’s look at a slide at the level of its million underlying hits. Imagine that the first of these million hits is appreciably more energetic than the others. If this were the case, then the start of the slide would acquire a crispness normally found in hits. But this hit would be just the first of a long sequence of hits, and would thus be part of the slide itself. Such a hit-slide would, if it existed, be neither a hit nor a slide.
And they do exist, for several converging reasons. First, slides have a tendency to be initiated by hits. Try sliding this book on a desk. The first time you tried, you may have bumped your hand into the book in the process of attempting to make it slide. That is, you may have hit the book prior to the slide (see Figure 5). It requires careful attention to gently touch the book without hitting it first. Now grab hold of the book and try to slide it without an initial hit. Even in this case there can often be an initial hitlike event. This is because in order to slide an object, you must overcome static friction, the “sticky” friction preventing the initiation of a slide. This initial push is hitlike because the sudden overcoming of static friction creates a sudden burst of many frequencies, as in Figure 4a. Slides, then, often begin with a hit. Second, hits often have slides following them. If you hit a wall with a straight jab, you will get a lone hit, with no follow-up slide. But if you move your arm horizontally next to the wall as you are hitting it—in order to give it a more glancing blow—there will sometimes be a small skid, or slide, after the initial hit.
Figure 5. A hit-slide is a fourth fundamental constituent of physical events. It sounds like a kind of phoneme in language called the affricate, which is like a plosive followed by a fricative.
Although a hit followed by a slide is a natural regularity in the world, a slide followed by a hit is not a natural physical regularity. First, it is common to have a hit not preceded by a slide. To see this, just hit something. Odds are you managed to make a hit without a slide first. Second, when there is a slide, there is no physical regularity tending to lead to a hit. Slides followed by hits are possible, of course—in shuffleboard, for example (and note the fricatives in “shuffle”)—but they really are two separate events in succession. A hit-slide, on the other hand, can effectively be a single event, as we discussed a moment ago.
If language sounds like nature, then we should expect linguistic hit-slide sounds to be more common than slide-hit sounds. Later in this chapter—in the section titled “Nature’s Words”—I will provide evidence that this is true of the way phonemes combine into words across human languages. But in this section I want to focus on the single-phoneme level. The question is, since hit-slides are a special kind of fundamental event atom, but slide-hits are not, do we find that languages have phonemes that sound like hit-slides, but not phonemes that sound like slide-hits?
Languages, like nature, are asymmetrical in this way. There is a kind of phoneme found in many languages called an affricate, which is a fricative that begins as a plosive. One example in English is “ch,” which is a single phoneme that possesses a “t” sound followed by a “sh” sound. In addition to words like “chair,” it also occurs in words like “congratulate” (spoken like “congratchulate”), and often in words like “trash” (spoken like “chrash”). Another example is “j,” which begins with “d” sound followed by a voiced version of the “sh” phoneme. Although we can describe “ch” as a “sh” initiated by a “t,” it is not the same sound that occurs when we say “t” and quickly follow it up with “sh.” The “ch” phoneme has the “t” and “sh” sounds bound up so closely to one another that they sound like a single atomic event. The “tsh” sound in “hotshot,” on the other hand, will typically sound different from “ch”; that is, we do not pronounce the word “ha-chot.”
Whereas language has incorporated nature’s hit-slide phoneme as one of its phoneme types, slide-hits, on the other hand, are not one of nature’s phonemes, and a harnessing language is not expected to have phonemes that sound like slide-hits. Indeed, that is the case. Languages do not have the symmetric counterpart to affricates—phonemes that sound like a plosive initiated by a fricative. It is not that we can’t make such sounds—“st” is a standard sound combination in English of this slide-hit form, but it is not a single phoneme. Other cases would be the sounds “fk” and “shp,” which occur as pairs of phonemes in words in some languages, but not as phonemes themselves.
By examining physics in greater detail, in this section we have realized that there is a fourth fundamental building block of events: hit-slides. And just as languages have honored the other three fundamental event atoms as their principal phoneme types, this fourth natural event atom is also so honored. Furthermore, the symmetrical fifth case, slide-hits, is not a fundamental event type in nature, and we thus expect—if harnessing has occurred—not to find fricative-plosives as language phonemes. And indeed, we don’t find them.
Slides that Sing
Recall that slides are, in essence, built from very many little hits in quick succession. The pattern of hits occurring inside a slide depends on the nature of the materials sliding together, and this pattern is what determines the nature of the slide’s sound. If you scrape your pencil on paper, then because the paper’s microscopic structure is fairly random, the sound resulting from the many little hits is a bit “noisy,” or like radio static, in having no particular tone to it. (The pencil scraping may also cause some ringing in the table or the pencil, but at the moment I want you to concentrate only on the sound emanating from the slide itself.)
However, now unzip your pants. You just made another slide. Unlike a pencil on paper, however, the zipper’s regularly spaced ribs create a slide sound that has a tonality to it. And the faster you unzip it, the higher the pitch of the zip. Slides can sing. That is, slides can have a ringlike quality to them, due not to the periodic vibrations of the objects, but to the periodicity in the many tiny hits that make up a slide.
Whether or not a slide sings depends on the nature of the materials involved, and that’s why the voice of a slide is an auditory feature that brains have evolved to take notice of: our brains treat singing and hissing slides as fundamentally different because these differences in slide sounds are informative as to the identity of the objects involved in the slides. Although slides can sing, it is more common that they don’t, because texture with periodicity capable of a ringlike sound is rare, compared to random texture that leads to generic friction sounds akin to white noise.
Do human languages treat singing slide sounds as different from otherwise similar nonsinging slide sounds? Yes. Languages have fricatives of both the singing and the hissing kinds, called the voiced and unvoiced fricatives, respectively. Voiced fricatives include “z,” “v,” “th” as in “the,” and the sound after the beginning of “j” (which you will recall is an affricate, discussed earlier in “Nature’s Other Phoneme”). Unvoiced fricatives include “s,” “f,” “th” as in “thick,” and “sh.” Just as singing slides will be rarer than nonsinging slides—because the former require special circumstances, namely, slides built out of many periodically repeating hits—voiced fricatives are rarer in languages than unvoiced fricatives. John L. Locke tabulated data in his excellent 1983 book, Phonological Acquisition and Change, and discovered that “s” is found in 172 of 197 languages in the Stanford Handbook
[1] (87 percent) and in 102 of 317 languages in the UCLA Phonological Segment Inventory Database (32 percent), whereas “z” (the voiced version of “s”) is found in 77 of 197 languages (39 percent) and 36 of 317 languages (11 percent), respectively. Similarly, “f” is found in 106 of 197 languages (54 percent) and in 135 of 317 languages (43 percent), whereas “v” is found in 61 of 197 languages (31 percent) and in 67 of 317 languages (21 percent), respectiv
ely. These data suggest that unvoiced slides are about twice as likely as voiced slides to be found in a language. (And notice how, in English at least, one finds voiced-fricative words with meanings related to slides that sing: rev, vroom, buzz, zoom, and fizz. One also finds unvoiced-fricative words with meanings related to unsung slides: slash, slice, and hiss.)
Voiced and unvoiced fricatives are found in languages because they’re found in the physics of slides. Hits can also be voiced or unvoiced, but for completely different physical reasons than slides. Zip up your pants and let’s get to this.
Two-Hit Wonder
Each day, more than a billion people wake to the sound of a ringing alarm, reach over, and hit the alarm clock, thereby terminating the ring and giving themselves another five minutes of sleep. In these billion cases a hit stops a ring, rather than starting one as we talked about earlier. Of course, the hit on the clock does cause periodic vibrations of the clock (and of the sleeper’s hand), but the sound of these vibrations is likely drowned out by the sound of the alarm still ringing in one’s ears.
Although hitting the snooze button of an alarm clock is not a genuine case of a hit stopping a ring, there are such genuine cases. Imagine a large bell that has been struck and is ringing. If you now suddenly place your hand on it, and keep it there, the ringing will suddenly stop. Such a sudden hand placement amounts to a hit—a hit that sticks its landing. And it is, in this case, by virtue of dampening, a hit that leads to the termination of a ring. Some dampening will occur even if your hand doesn’t stick the landing, so long as you hit the bell much less energetically than it is currently ringing; the temporary contact will “smother” some of the periodic vibrations occurring in the bell.
Although in such cases it can sound as if the bell’s ringing has terminated, in reality one can leave the bell with a residual ring. A hit on a quiet bell would sound like an explosive hit, because in contrast to the bell’s stillness, the hit is a sudden discontinuous rise in the ringing magnitude. But that same hit on an already very loudly ringing bell causes a sudden discontinuous drop in the ringing magnitude. In contrast to the loud ringing before the hit, the hit will sound like the sudden ceasing of a ring, even if there is residual ringing.
Hits, therefore, have two voices, not just the one we discussed earlier in the section called “Nature’s Phonemes.” Hits not only can create the sudden appearance of a wide range of frequencies, but can also sometimes quite suddenly dampen out a wide range of frequencies. These two sounds of hits are, in a sense, opposites, and yet both are possible consequences of one and the same kind of hit. This second voice is rarer, however, because it depends on there already being a higher-energy ring before the hit, which is uncommon because rings typically decay quickly. That is, the explosive voice of hits is more common than the dampening voice, because most objects are not already ringing when they are hit.
If languages have harnessed our brain’s competencies for natural events, then we might expect languages to utilize both of these hit sounds. And indeed they do. The plosives we discussed earlier consisted of an explosive release of air, after having momentarily stopped the airflow and let pressure build. But plosives also occur when the air is momentarily stopped, but not released. This happens most commonly when plosives are at the ends of words. For example, when you utter “what” in the sentence “What book is this?” your mouth goes to the anatomical position for a “t,” but does not ever release the “t” (unless, say, you are angry and slowly enunciating the sentence). Such instances of plosive stop sounds are quite common in language, but less so than released plosive sounds—there are many languages that do not allow unreleased plosives, but none that do not allow released plosives. John Locke tabulated from the Stanford Handbook that, in 32 languages that possessed word-position information, no plosives were off limits at word starts (where they would be released), but 79 plosives were impermissible at word-final position (where they are typically unreleased). Also, among the words we collected from 18 languages, 16,130 of a total of 18,927 plosives, or 85 percent, were directly followed by a sonorant (and thus were released), and therefore only 2,797 plosives, or 15 percent, were unreleased. And even in languages (like English) that allow both kinds of plosive sounds, plosives are more commonly employed in their explosive form, something we will talk about in a later section (“In the Beginning”). This fits with the pattern in nature, where explosive hits are more common than dampening hits.
Not only does language have both hit sounds as part of its repertoire, but, like nature, it treats the unreleased “t” sound and the released “t” sound as the same phoneme. This is remarkable, because they are temporal opposites: one is like a little explosion, the other like a little antiexplosion. One can imagine, as a thought experiment, that people could have ended up with a language that treats these two distinct “t” sounds as two distinct phonemes, rather than two instances of a single one. In light of the auditory structure of nature, however, it is not at all mysterious: any given hit can have two very different sounds, and language carves at nature’s joints.
In light of the two sounds hits make, there is a simple kind of sound we can make, but that language never includes as a phoneme: “beep,” like an electronic beep or like Road Runner. A beep consists of a sudden start of a tone, and then a sudden stop. Beeps might, at first glance, seem to be a candidate for a fundamental constituent of communicating by sound: what could be simpler, or more “raw,” than a beep? However, although our first intuitions tell us that beeps are simple, in physics they are not. In the real world of physical events among objects, beeps can only happen when there is a hit (the abrupt start to the beep), a ring that follows (the beep’s tone), and a second hit, this one a dampening one (the abrupt beep ending). A “simple” beep can’t happen in everyday physics unless three simple constituent events occur. And we find that in languages as well: there are no beeplike phonemes. To make a beep sound in language requires one to first say a plosive of the released kind, then a (nonwiggly) sonorant, and finally an unreleased plosive . . . just like when we say the word “beep.”
Hesitant Hits
Bouncing a basketball could hardly be a simpler event. A bounce is just a hit, followed by a ring. And as we discussed earlier, the sound is a sudden explosion of many frequencies at the initiation of the hit, followed by a more tonal sound with a timbre due to the periodic vibrations of the basketball and floor. Although hits seem simple, they become complicated when viewed in super slow motion. After the ball first touches the ground, the ball begins to compress, a bit like a spring. After compression, the ball then decompresses as it rises on its upward bounce. Although these ball compressions and decompressions are typically very fast, they are not instantaneous: the physical changes that occur during a hit occur over an extended period of time, albeit short. What happens during this short period of time depends on the nature of the objects involved.
One of the most important acoustical observations about collisions is that ringing doesn’t tend to occur until the collision is entirely finished. There are several reasons why this is so. First, the ground rings less during the collision because even though the ground has already been struck, the ball’s contact with the ground dampens the ground’s vibrations. Similarly, the ground’s contact with the ball dampens the ball’s vibrations. Second, during the ball’s compression, its shape is continually varying, and so any vibrations it is undergoing are changing in their timbre and pitch very quickly, far more quickly than the ring-wiggles we discussed earlier. In fact, the vibration changes occur at a time scale so short that any rings that do occur during the collision will not sound like rings at all. Third, during the period of the collision when the ball is not yet at maximum compression, the ball is continually hitting new parts of the ground. This is because, as the ball compresses, the ball’s footprint on the ground keeps enlarging, which means that new parts of the ball continually come into contact with the ground. In fact, even if the surface area of contact never en
larges, the mass in parts of the ball continues to descend during the ball’s compression, providing further impetus upon the surface area of contact. Because the compression period is filled with many little hits, any ringing occurring during compression will have a tendency to be drowned out by the little hits.
For several converging reasons, then, the ringing that occurs after a hit doesn’t tend to begin until the compressions and decompressions are over. For the basketball, the ringing occurs most vigorously when the ball rebounds back into the air. There is a simple lesson from these super slow motion observations: there is often a gap between the time of the start of a collision and the start of the ringing.
What determines the length of these hit-to-ring gaps? When your basketball is blown up fully, and the ground is firm, then the time duration of the contact with the floor is very short, and so the gap between the start of the hit and the ring is very small. However, when the ball is fairly flat—low in pressure—it spends more time interacting with the ground. Bouncing a ball on soft dirt would also lead to more ground time (see Figure 6). Figure 7a shows the sound waveform signal of a book falling onto a crumpled piece of paper—producing similar acoustics (in the relevant respects here) to those of a ball dropped on soft dirt—and one can see a hit-to-ring gap that is larger than that for the same book falling directly onto the table. For the flat basketball, then, the gap between hit and ring is larger than that for the properly blown-up ball.
Harnessed: How Language and Music Mimicked Nature and Transformed Ape to Man Page 6