How rhythm shapes our lives
Nina Kraus / BBC:
My husband reads to me every night before we go to sleep. We deliberately choose books that are familiar – oft-read children’s classics make frequent appearances – so I do not worry about missing something important when I drift off. I have noticed that after some time – it can be as little as a few minutes if I am especially tired – the meanings of the words are gradually eclipsed by the sounds. I begin to hear sounds and rhythms instead of words and story. The waxing and waning of the accents and stress patterns become a calming, lulling, treasured experience that soothes and resets me after a long day. Why do we care about rhythm? It connects us to the world. It plays a role in listening, in language, in understanding speech in noisy places, in walking, and even in our feelings toward one another.
Rhythm is much more than a component of music. We experience the rhythmic changes of the seasons. Some of us have menstrual cycles. We have circadian rhythms – daily cycles of mental and physical peaks and troughs. Frogs croak rhythmically to attract mates and change their rhythm to signal aggression. Tides, 17-year cicadas, lunar phases, perigees, and apogees are other naturally occurring rhythms. Human-made rhythms include the built world – street grids, traffic lights, crop fields, mowed designs in baseball diamond outfields, the backsplash behind the kitchen counter, spatial patterns in geometric visual artforms.
Music and rhythm are rooted in every known culture. What parent does not use rhythmic rocking to soothe a crying baby? The repetitive sounds and silences that comprise rhythmic patterns make dancing possible, aid in the memory and reproduction of music, and facilitate group singing, playing, or drumming. Rhythm has been used for millennia to tie societal members together – the chants of a religious order or the cadence calls of military ranks are just two examples. Poetic works thousands of years ago, such as those of Homer, were chanted or sung with rhythm serving a mnemonic function. Repetitive or complex work engenders rhythmic accompaniment, in some cases to break the monotony, in others to actually help you perform the work better. Workers performing hard labour such as rock breaking chant to keep their sledgehammers swinging in rhythm. Postal workers in Ghana hand-cancel stamps with a distinct rhythm. Rug weavers in Iran use chants with a complex musical structure to communicate weaving patterns to their co-weavers. All musical systems and styles have organisational rhythmic motifs. Indeed, the very universality of rhythm is a strong argument for the existence of biological processes governing the perception and production of rhythm. Rhythms in the brain have been called out as a basis for consciousness itself. Language probably does not immediately come to mind when we think of rhythm. You might have had a high school literature class where you learned about prosodic feet – iambs, trochees, and anapests. But outside the context of poetry, we rarely think about speech having a particular rhythm. After all, we are likely to say “Oy Bill – you ready yet?”. Not, “Hey there Bill,/do you think/it is now/time to go?” so that it conforms to dactylic tetrameter. What about rhythm and reading? Here, too, we are unlikely to associate rhythm to reading unless we are reading poetry. In fact, rhythm is a necessary ingredient of linguistic communication itself. Rhythm can be viewed through the lens of shorter and longer time scales. Speech has phoneme, syllable-, word-, and sentence-length rhythmic units, each unfolding at their own rate. We understand that speech comes in different sized units – the sound an individual letter makes, the phoneme, at one extreme, and the slowly rising and falling loudness and pitch contours that unfold over the course of a sentence or group of thoughts on the other. This latter one is the night time reading rhythm I fall asleep to. These entwined elements of speech constitute rhythms that must be sorted by our sound minds. We can try to focus on the slow parts of speech (say, the fluctuating pitch of the voice) and ignore the fast (the vowel and consonant sounds that convey the meaning of the words) or vice versa. But this is usually not possible and rarely desirable. This temporal hierarchy is at work in music too. Music is a mix of slow phrases, steady beats, sustained notes, rapidly changing notes, trills, and drum crashes. Entwined temporal structures are in environmental sounds as well – when walking through the woods, we simultaneously hear slow footsteps, the unfolding crunch of leaves underfoot, and the rapid snap of a twig. Much as sound units come in different lengths, brain rhythms come in different speeds. Subcortical structures are equipped for microsecond timing while the cortex is better suited to integrating sounds over a longer time scale. Brain rhythms can be measured both when at rest and when performing an activity. When listening to speech, there are fast brain rhythms that entrain to the fast phonemes, the near instantaneous consonant sounds. Middle-range rhythms in the brain track the rate of syllables. Slower brain rhythms correspond to the slow oscillations of phrases and sentences. Similar nested brain patterns are active when listening to music. Imagine a metronome ticking at about 144 beats per minute (bpm). Popular songs in this range include Blondie’s “Call Me”, the Beatles’ “Back in the USSR”, and the Rolling Stones’ “(I Can’t Get No) Satisfaction”. It’s a fast, allegro rate. Measured another way, these songs have about a half second between their beats. If we play a conga drum by itself at this rate and record brain waves to it, we will see neural activity repeating every half second (boom, boom, boom, boom, or “one, two, three, four”). But what does the brain do if you listen to the conga drumming along to a song that matches this beat? The brain produces a new rhythm. In addition to a response peak every half second (where musically speaking the “ones” are), you see another, smaller peak halfway in between (1 and 2 and 3 and 4 and; “FLEW in FROM mi-AM- i BEACH”). The brain has worked out the strong/weak pairs comprising the song’s meter.
This tells us the brain entrains and reinforces both explicit and implied rhythms in the music. This extra rhythm in the brain wave does not occur when the song is deliberately misaligned with the conga beat. A similar example of the brain creating a beat comes from Brainvolts alum Kimi Lee, who found that the fundamental frequency of an identical speech sound is enhanced when it occurs on the “one” in a four-beat sequence. The sound mind’s response to a drumbeat is deeply shaped by its aural context. Rhythmic organisation operates automatically when we listen to sound. If our rhythmic expectations are violated, our brains behave in a different manner because of our inherent internal sense of rhythm. magine the familiar rhythm “Shave and a haircut, two bits” and tap it out on a table with your finger.
Did you tap seven times? Now imagine it again and tap your foot to it. Did you tap seven times again? Or fewer? For me, when I tap my finger on a table, I tap to every note (ignoring the rests). When I tap my foot or snap my finger along to music, I typically tap or snap to the beat (or pulse) of the song, not every note. When I tap my finger on the table, hitting the “sounds” and ignoring the “silences,” I am tapping out the rhythmic pattern – I am keeping track of how long or short each note is and where the pauses occur.