Musical Dolphins

Can the Study of Music Inform Science?

*Author’s Note: The following post will contain interesting scientific findings as well as (frequently wild) speculation by yours truly. Please take the latter as more food for thought than serious scholarly argument.

Let’s begin with an imagined scenario. You are traveling with your friends, specifically out looking for a place to eat. You’re not in a heavily populated area and there are few choices, so it takes a while. Eventually, you locate a source of sustenance and indulge yourselves. Satisfied, you depart, but as you do you encounter another group. They seem friendly enough, and are also looking for food, so you decide to introduce yourselves and help them out a bit. Eventually, your turn comes to pronounce your name.

It comes out as a string of music.

This occurrence does not apply to human interaction, but it may very well be a common event for a dolphin.

In 2013, Arik Kershenbaum (now of the University of Cambridge), Laela Sayigh (of Woods Hole Oceanographic Institute) and Vincent Janik (of the University of St. Andrews) published an interesting study on the categorization of signature whistles (Kershenbaum et al. 2013). A signature whistle is an individual identifier for a dolphin, essentially a name, used mainly when the dolphin in question is separated from its companions or when it is meeting new dolphins.

kershenbaumfig1 sigwhistles

Spectrograms of Signature Whistles (Figure 1 from Kershenbaum et al. 2013)

The premise of the study was simple enough. In order to classify signature whistles (taking a large amount of whistles recorded in the field and sorting them by which dolphin each whistle belongs to), many studies up to this point have used human observers who look at spectrograms—a plot of sound frequency (or pitch) over time—of the different whistles and try to match the dolphin they belong to. Human visual inspection is the most reliable method used, but it is also very time consuming. The researchers wanted to find out if other methods would work in classifying signature whistles to save time. They used two computer algorithms that have been developed in other studies (the correlation metric and the dynamic time-warping metric, both detailed mathematically in the paper), but also used an algorithm based on the Parsons code (Kershenbaum et al. 2013).

 

This was a fascinating choice. The Parsons code is widely used already—as an algorithm applied to music retrieval databases (Downie 2003). It functions by defining each note based on the note before it (or time step in the musical score), using “*” to define the first note and labeling each of the next notes depending on if they repeat (“r”), go down in pitch (“d”), or go up in pitch (“u”). So, the first line of “Twinkle Twinkle Little Star” would be “*rururd.”

The most interesting part of the findings was that this Parsons code-based algorithm actually performed significantly better than the two other computer algorithms in correctly identifying which signature whistles belonged to the same dolphin (Kershenbaum et al. 2013). While it was still not as effective as human sorting, the fact that this was the first use of such an algorithm and so lacking in refinement meant this was a significant finding, potentially leading to a new, much faster way of sorting signature whistles.

The striking part of the findings to me, though, was the fact that a music-sorting code was able to perform comparatively well in the task of sorting whistles made by dolphins. Are dolphin whistles inherently musical?

First, it is important to take into account that both of the most effective means of sorting signature whistles were based on the contour of the whistle (the pattern of frequency change over time). Human observers could view the overall shape of the contour quite easily, seeing it directly imaged on a spectrogram. The Parsons code works in much the same way, defining a contour in simple terms. The code works in retrieving music because the contour of the music is one of the most important features in the memorization of the music itself (Dowling 1978, Downie 2003). It would appear that this feature of human perception, the frequency contour of music, is also important to dolphins, since it is the primary way to differentiate between different signatures. This makes dolphin signatures different from human names, since there are no consonants or vowels involved but only changes in pitch in a specific order.

Of course, there are many human languages that rely on pitch to convey meaning (tonal languages like Mandarin Chinese or Hmong) (McWhorter 2015). So, if we are going to compare the dolphins’ whistles to any aspect of human communication, would they be more like a tonal language or more like music? Aspects of their behavior lead me to consider the latter option.

There are other aspects of dolphin communication that have been likened to music—the most telling of which is chorusing along with other synchronous vocalizations. Janik et al. (2011) reported instances of groups of offshore bottlenose dolphins (between two and six) in the Gulf of Mexico producing the same whistle type almost simultaneously, something rarely seen even in other dolphins (they found no instances in a few inshore populations). Herzing (2006, 2015) described a behavior seen in both Atlantic spotted dolphins and bottlenose dolphins in the Bahamas in which the dolphins would synchronize calling (using either squawks, whistles, buzzes, or brays), often in rhythmic patterns, during bouts of aggression. In some cases, the dolphins even synchronized their body posturing to the rhythm of their calls (Herzing 2015).

herzing2015 fig1 synchronous calls

Bottlenose Dolphins Use Ritualized Synchronous Calls (Figure 1B from Herzing 2015)

Such behavioral synchrony, especially in the vocal realm, was possibly very important in early human development. Merker (2000) described chorusing as a human behavior which probably aided in language development (through vocal learning) and the development of advanced social systems and rituals as well as leading directly to more sophisticated forms of music. “Synchronous chorusing and dancing to a repetitive beat qualifies as music in the human sense,” Merker postulated, which is possibly what the dolphins in Herzing’s reports were doing.

 

So does that mean dolphins are musical? There are plenty of alternative explanations and careful considerations to make before calling their behavior or communication definitively musical in the proper sense, but the idea itself might not be so farfetched. To understand why, we must learn more of the dolphin brain.

Neuroscience might just hold the key to understanding if dolphins are capable of music. Many neurological findings lead to the conclusion that dolphins have one of the most sophisticated emotional processing systems of any animal, possibly including humans. A great deal of research shows that dolphins have advanced social systems and the neuroanatomy to support advanced cognition, especially in the social and emotional realms (Marino et al. 2007). Many specific components of their brains specifically illustrate their emotional capabilities. The dolphin brain has a well-developed anterior insular cortex (AI) which “may be the equivalent” of the primate AI (Jacobs et al. 1984).

buttifig2 ai brain region

The Anterior Insular Cortex (AI) of the Dolphin Brain (Figure 2 from Butti et al. 2009)

The AI is very important to social emotions in humans, playing roles in traits like empathy, compassion, interpersonal relations, and in predicting emotional states of self and others (Lamm & Singer 2010). Dolphin brains also have a comparable number of Von Economo neurons (VENs) to those of humans, great apes, and elephants (Butti et al. 2009). VENs, also called spindle cells, are extra-large neurons important in social and emotional cognition, awareness, and intuition (Allman et al. 2005). Dolphins even have VENs present in the AI (Butti et al. 2009). As well as these specific structures, the generalized organization of the dolphin brain is conducive to advanced emotional processing. Based on communication with Denise Herzing, Thomas White explained that the dolphin limbic system (the processor of base or primitive emotions in mammals) may be connected to more portions of the brain than in humans and other primates, leading to a higher prominence of emotions in decision-making and behavior (White 2007). Dolphins may base more of their behaviors and social interactions around emotions and relationships.

 

With this in mind, it is not surprising that dolphins engage in ritualized synchronous calling and posturing (at the very least the precursors to human song and dance if not full-fledged music). Music is, after all, the language of emotion. Through arcs and dances of pitch and steady beats, we speak more of emotion than in hundreds of words. Perhaps dolphins, valuing emotion and relationships over rational discussions, speak more in music than in so many words.

In his book, Thousand Mile Song, David Rothenberg summarized an arranged encounter between a musician, trained in recognizing different tones and voices in a score, and a recording of several dolphins interacting. The musician was able to piece together the different components of the interaction better than the scientists could, which might make more sense now. It could help us learn more of their perception and behavior of we keep in mind that dolphins might communicate at times like different instruments in a symphony, “speaking” of emotion and connection more than anything else.

 

WORKS CITED

Allman, J. M., Watson, K. K., Tetreault, N. A., & Hakeem, A. Y. (2005). Intuition and autism: a possible role for Von Economo neurons. Trends in Cognition Science 9, 367-373.

Butti, C., Sherwood, C. C., Hakeem, A. Y., Allman, J. M., & Hof, P. R. (2009). Total Number and Volume of Von Economo Neurons in the Cerebral Cortex of Cetaceans. The Journal of Comparative Neurology 515, 243-259.

Dowling, W. J. (1978). Scale and Contour: Two Components of a Theory of Memory for Melodies. Psychological Review 85 (4), 341-354.

Downie, J. S. (2003). Music Information Retrieval. Annual Review of Information Science and Technology 37, 295-340.

Herzing, D. L. (2015). Synchronous and Rhythmic Vocalizations and Correlated Underwater Behavior of Free-ranging Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus) in the Bahamas. Animal Behavior and Cognition 2 (1), 14-29.

Herzing, D. L. (2006). The Currency of Cognition: Assessing Tools, Techniques, and Media for Complex Behavioral Analysis. Aquatic Mammals 32 (4), 544-553.

Janik, V. M., Simard, P., Sayigh, L. S., Mann, D., & Frankel, A. (2011). Chorussing in delphinids. Acoustical Society of America 130, 2322.

Jacobs, M. S., Galaburda, A. M., McFarland, W. L., & Morgane, P. J. (1984). The Insular Formations of the Dolphin Brain: Quantitative Cytoarchitectonic Studies of the Insular Component of the Limbic Lobe. The Journal of Comparative Neurology 225, 396-432.

Kershenbaum, A., Sayigh, L. S., & Janik, V. M. (2013). The Encoding of Individual Identity in Dolphin Signature Whistles: How Much Information Is Needed? PLOS ONE 8 (10), 1-7.

Lamm, C., & Singer, T. (2010). The role of anterior insular cortex in social emotions. Brain Structure and Function 214, 579-591.

Marino, L., Connor, R. C., Fordyce, E., Herman, L. M., Hof, P. R., Lefebvre, L., Lusseau, D., McCowan, B., Nimchinsky, E. A., Pack, A. A., Rendell, L., Reidenberg, J. S., Reiss, D., Uhen, M. D., Van der Gucht, E., & Whitehead, H. Cetaceans Have Complex Brains for Complex Cognition. PLoS Biology 5 (5), 0966-0972.

Merker, B. (2000). Synchronous Chorusing and Human Origins. In The Origins of Music. Wallin, N. L., Merker, B., and Brown, S. (eds). MIT Press, MA, USA. 315-327.

McWhorter, J. (2015). “The World’s Most Musical Languages.” The Atlantic. <http://www.theatlantic.com/international/archive/2015/11/tonal-languages-linguistics-mandarin/415701/&gt;

Rothenberg, D. (2008). Thousand Mile Song: Whale Music in a Sea of Sound. Basic Books, NY, USA.

White, T. I. (2007). In Defense of Dolphins: The New Moral Frontier. Blackwell Publishing, MA, USA.

 

 

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