The art of synchronization

Synchronization is a well-known and important natural phenomenon, from planets and galaxies to subatomic particles, from ultra-fast lasers to slow springs and metronomes. “Many things in nature, living and non-living, synchronized by the very fact of being a network,” explains doctoral student Shir Shahal. “The best-known example is the flight of the starlings. The birds fly next to each other, not a group; each one is only aware of the birds closest to it, and still – they perform this uncoordinated dance with the goal of defending themselves against predators. So how does that happen? One bird senses a disturbance and shifts sideways. The ones next to it notice and adjust accordingly, and so on, creating a defense-based synchronization among the birds. Schools of fish do that, too, and camels as well. But synchronization doesn’t have to be driven by self-defense: fireflies, for example, synchronize their lights for the sake of mating – that’s how males attract the females.”

“Humans too are tribal animals, and something inside us wants to stay in synch. Synchronization in humans can be seen, for example, in applause: a show ends and every person in the crowd starts clapping to their own rhythm – but without noticing, they adjust themselves to the sounds around them, and the applause becomes unanimous. We can also see synchronization in people riding elevators – we tend to automatically face the doors; there was also a study in Russia that showed how stockbrokers earn more when they are in synch. It’s an important phenomenon, even lifesaving in times of disaster, and should be accounted for: a few years ago, a pedestrian bridge was erected in London but was closed off two days after opening. It was built by the finest architects, but they failed to take into human synchronization into account, and the fact that this synchronization has a rhythm; all of the pedestrians walked at the same pace, creating significant – even dangerous – tremors.”

Synchronization, in animals as well as humans, has been well studied – see the applause example – with the key assumption that the correct model for describing human synchronization is that of coupled oscillation, which depicts synchronization in nature. “However,” says Dr. Moti Fridman, “that model doesn’t account for a uniquely-human feature: our ability to ignore or tune out. This creates a very different dynamics within human networks.”

Ignorance is bliss

Fridman (41) specializes in holographic, lasers, nonlinear optics and temporal optics. He established the temporal optics and fiber devices lab where he researches a variety of fields, including rogue wave patterns. Shahal (37) is a former oboist, a Thelma Yellin graduate, and a former IDF musician with a degree in musicology from the Jerusalem Academy of Music and Dance. “Up until the age of 26, my life revolved around music. Then, once I graduated from the academy, I decided to pursue physics at Bar Ilan. That’s how I met Moti.”

Their research on human network synchronization, reviewed in an article in Nature Communication Magazine, started out as a project for the Joseph Fetter Museum of Nanotechnology. The museum, an initiative of Bar Ilan’s Institute for Nanotechnology and Advanced Materials, showcases projects that incorporate art and science. Conducted in collaboration with composer and sound artist Elad Shniderman, the research explored musical synchronization. “We took 16 violin players, sat them in a circle, and obstructed their field of vision to prevent them from synchronizing according to their bows. We provided them with electric violins, complete with a cable connected to our mixing system, and noise-canceling headphones so they could only hear what we were playing. Then we let them play the same musical phrase, composed by Elad and Shir, over and over again,” recalls Fridman. “Our only instruction was for them to try and synchronize themselves to what they were hearing. They didn’t have to maintain the rhythm – only synchronize. We obviously made sure that each player could hear themselves so that they could play, and in addition, enabled each player to hear their nearest neighbors. In other words, we created a system that allowed us to cleanly explore a human network: it eliminated background noises and let us control all of the parameters that determine how the network behaves.

At first, everyone could hear everyone else, as is the case with orchestras, and very little coupling was needed for everyone to synchronize. “At the first stage,” says Fridman, “At only we let them hear themselves and their two nearest neighbors – immediate right and immediate left – and that required a higher volume, higher coupling, to allow them to synchronize. But that was to be expected. The interesting thing happened once we imposed delay – violinist A heard what violinist B played a little while earlier, and violinist B heard what violinist A played a little while earlier. There was no way for them to synchronize, and we predicted that they would form an average, like with springs or lasers. But they didn’t; they gave up. At first, they simply slowed their pace down, but once the delay reached approximately 0.5 seconds, one of them would give up and stop listening to the other, so that one player would play while ignoring what they were hearing, and the other one would follow.”

“We continued to expand the delay, and once it reached half the duration of the phrase, we achieved stability once more as the players were again able to synchronize and follow one another,” explains Fridman. “It got so stable that if we continued to extend the delay, the players simply slowed down their pace and maintained a steady delay of half the phrase length. Once they found the out-of-phase state, they wouldn’t let go.”

“It was an extraordinary experience, almost psychedelic,” recounts Ateret Wirtzberg (29), a master’s student at the Faculty and an alumnus of the music conservatory, who participated in the experiment under two titles: as a violinist, and as a result analyst. “Throughout the experiment, I couldn’t see the other players, but at the end of each take I saw the looks on their faces – they were all confused and didn’t really know how to contain the experience. Later, when I looked at the results, I saw that there was a half-phase delay, but I remembered everyone playing together – so how could that be? Then I realized that the reason I heard everyone playing together was that the delay was always half the playing period, so what I heard was actually two delays that converged into a single cluster.”

A new – and precise – model

All that is true for an even number of players, but what happens when the signal is odd – three players, for example? “In that case,” says Fridman, “we can’t have full synchronization, because two of the three may be in synch, but the third will always be in-phase with one player and out-of-phase with the other, creating frustration.”

“Frustration is the precise word to describe the situation,” says Wirtzberg, “when you’re playing and not thinking about it, you have a fraction of a second to decide what to do, and not always consciously. It’s a completely different situation than what we’re used to as players in an orchestra, where the goal is to play together – but here, you’re presented with obstacles, or deprived of the ability to synchronize. It’s an extraordinary experience and you’re confronted with it at any given moment. I remember not knowing what to do – slow down, pick up – and eventually I just went along with someone. Then I saw the results and realized that everything followed a pattern, and my unconscious decision was actually directed. I think that in some places, the results were positively surprising in terms of how unanimous and distinct it was. It didn’t happen to a single-player – it happened to all of them and can be explained. It was an incredible thing to witness.”

Here again, says Fridman, the matter of ignorance was distinctly present. “the players consistently chose to follow one player and ignore the other. Once they did that, they changed the links of the system, because they decided to ignore one of the links. That’s what’s so special about the human network. People change and disband the links and chose others until they find a system in which they can find the out-of-phase state. This is called atrophy, and it causes the system’s dynamics to be completely different than that which you would expect from a normal network of coupled items – which proves that the regular model of paired oscillators doesn’t work for describing human systems. That is why we developed a new model for describing human network synchronization, one that is more flexible and precise, and takes into account the fact that a person can ignore one input and acknowledge another.”

Not only did the experiment yield a new model, but also a piece of art, currently presented at the Joseph Fetter Museum of Nanotechnology. Composer Elad Shniderman used the results of the study and composed a designated piece for 16 players playing in delay. Museum visitors can listen and watch the entire concert on 16 separate screens.