Springtime has officially come to Ithaca, and, along with it, a chorus of songbirds from robins to cardinals to finches. While these melodies may seem ordinary, according to Prof. Michael Goldstein, psychology, a songbird’s song is more than just sonorous chirping — it can reveal the mechanisms of language development in humans.
Goldstein studies vocal learning in both human infants and songbirds, specifically zebra finches. He is particularly interested in the social factors behind these processes.
“Different species use song in different ways. There’s no such thing as a generic songbird. Some songbirds use their song for mate attraction, some use it for territory defense, some use it for both in different contexts,” Goldstein said.
According to Goldstein, if one of the main purposes of birdsong is mate attraction, then a song’s quality can be measured by the response it elicits in potential mates. Goldstein proposed measuring the quality of birdsong by using a “female bioassay” — essentially testing the degree to which females like and respond to a given song.
Goldstein explained that higher-quality songs likely demonstrate a mate’s higher fitness or health because “it takes a lot of energy and a lot of motor control to properly articulate a song.”
Zebra finches start producing begging calls around ten days after hatching. After 30 days, they start making “what’s called subsong, and then plastic songs that are analogous to a baby babbling,” Goldstein said. Subsongs consist of short, variable syllables, while plastic songs are slightly more similar to adult birdsong but still very subject to change.
By around day 90, that song becomes “crystallized” and will not develop any further. Zebra finches don’t learn new song past this stage, but what happens between the start of vocalization and the crystallization of song is key — Goldstein has found that young zebra finches rely on social feedback from their parents in order to produce better song.
“Dads will sing contingently on the babies’ immature vocalizations. Moms give gestural responses, little wing movements, what are called wing strokes and fluff-ups. The young use this information, contingent on their song, to build a better song,” said Goldstein.
A 2017 study, co-written by Goldstein and co-written by Samantha Carouso grad and Nicole Baran grad tested this idea of social learning in zebra finches. A group of zebra finches were manipulated to have enhanced receptors of vasotocin, a hormone similar to oxytocin that is related to social behavior. In particular, this small peptide has been found to play a role in bonding, competition, vocalizations and many other behavioral features.
Another group was given manning compound, a vasotocin receptor blocker, essentially making those finches less socially attuned. A control group was given saline.
The study found that the quality of song was related to how “socially attuned” each finch was, based on whether their vasotocin receptors were enhanced or blocked. This study highlights the importance of social learning in song development.
This learning process is therefore similar to language development in humans, particularly regarding the importance of feedback. When babies babble, they rely on feedback from their parents, very similarly to how young zebra finches develop their songs based on the responses they receive from their parents. By making plastic song or babbling, both species create learning opportunities for themselves.
One factor influencing these similarities in vocal development between zebra finches and humans might be brain structure. According to Goldstein, both the song learning circuits in birds and speech learning areas in humans share some overall patterns of connectivity. There are connections between basal ganglia areas such as the ventral tegmental area, responsible for reward and motivation, and areas that are responsible for vocal learning and production in both birds and humans.
“At the brain level, there are parallels in connectivity between areas responsible for things like social reward and motivation and areas responsible for song or speech production,” Goldstein said.
This idea of social feedback in language development could be very important when considering atypical development. For instance, infants with Down syndrome babble more slowly, which can lead to different reactions in parents and can potentially affect vocal learning.
In addition to Down syndrome, Goldstein’s research on vocal development has countless applications. In particular, he cited a better understanding of atypical vocal development in infants born with autism, infants receiving cochlear infants for deafness and infants born into lower socioeconomic households.
“By putting development into social context, we’re gaining a better understanding of the biological and social mechanisms that drive developmental change in communication systems, and because we’re doing it in multiple species, that gives us insight into how development itself has evolved — both the evolution of communication as well as the development of communication,” Goldstein said.