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Welcome to the Laboratory of Vocal Learning at Hunter College

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Learning vocal sequences: a comparative study across songbirds and human infants

Both birdsong and human language rely on the ability to arrange syllables in new sequences. We developed an experimental technique for presenting zebra finches with sequence rearrangement tasks:

 

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We can now ask the bird: can you swap the order of these sounds? Can you insert this syllable into that string? Birds were able to solve these tasks, but never in a single step. Instead of swapping syllable order or inserting syllables into strings, the birds solved those tasks in a series of steps, gradually approximating the target syntax. For example, to transform the song ABC-ABC to ACB-ACB, the bird learns one transition, say CB (and sings ABCB-ABCB for awhile), a few days later it might learn a second transition, say AC. Finally, once the bird learned the third transition BA, it promptly switches to the target ACB-ACB song, and will never sing ABC again. We found that Bengalese finches learn their more complex song in a similar manner. Strikingly, human infant babbling also develops in a similar manner: each uttered syllable is first performed singly, reduplicated, or at an utterance edge. Then, over 20 weeks or so, the new syllable type gets connected to other syllables in a stepwise manner. Eventually, the infant can babble 'freely' but this is not the starting point of vocal learning -- it is an endpoint of an elaborate developmental process, where combinatorial abilities are gradually acquired. This slow process can explain the developmental gap between the early perceptual capabilities to perceive complex vocal sequences, and the delayed motor capabilities of producing them.

Click here to watch a short movie demonstrating the effect

Click here to read our Nature paper about the development of vocal combinatorial abilities in songbirds and human infants

 

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Vocal exploration is locally regulated during song learning

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Birdsong is highly variable during learning. This variability is generated by the Anterior Forebrain Pathway to allow vocal exploration. How is this variability regulated? Is it evenly distributed across song elements, or perhaps controlled over fine time scales? To test this question, we manipulated song learning in zebra finches to experimentally control the requirements for vocal exploration in different parts of their song. We first trained birds to perform a one-syllable song, and once they mastered it, we added a new syllable to the song model. We found that when practicing the modified song, birds rapidly alternated between high and low acoustic variability to confine vocal exploration to the newly added syllable. Furthermore, even within syllables, acoustic variability changed independently across song elements that were only milliseconds apart. The variability of each song element decreased as it approached the target, suggesting that vocal error is computed locally in subsyllabic timescales and that song elements can be learned and crystallized independently.
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Images of song perception: How early auditory experience shapes auditory fMRI responses in songbirds

 

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Juvenile male zebra finches develop their song by imitation. Females do not sing but are attracted to males’ songs. With functional magnetic resonance imaging and event-related potentials we tested how early auditory experience shapes responses in the auditory forebrain of the adult bird.

Adult male birds kept in isolation over the sensitive period for song learning showed no consistency in auditory responses to conspecific songs, calls, and syllables. Thirty seconds of song playback each day over development, which is sufficient to induce song imitation, was also sufficient to shape stimulus-specific responses.

Strikingly, adult females kept in isolation over development showed responses similar to those of males that were exposed to songs. We suggest that early auditory experience with songs may be required to tune perception toward conspecific songs in males, whereas in females song selectivity develops even without prior exposure to song.

Click here to read Kristen Maul dissertation about how early auditory experience shapes auditory fMRI and ERP responses

Co-authors: Kristen Maul, Henning Voss, Santosh Helekar, Lucas Parra

 

Culture in the lab: development of song culture in the zebra finch

Zebra finch raised in isolation develop abnormal songs. We designed an experiment to determine whether wild-type song culture might emerge over multiple generations in an isolated colony founded by isolates. In tutoring lineages starting from isolate founders, we quantified alterations in song across tutoring generations.

We found that juveniles imitated the isolate tutors but changed certain characteristics of the songs. These alterations accumulated over learning generations. Consequently, songs evolved towards the wild-type in three to four generations. Thus, species-typical song culture can appear de novo.

 

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Click here to download our Nature article about development of song culture

Click here to read Olga Feher's PhD dissertation about song culture

Click here to download examples of song-culture development

 

How a song is born

Zebra finches learn their song during two months of development (days 30-90 post hatch). Over that time, they listen to adult birds (tutors) and produce 1-2 million song syllables.

We record ALL of them. The images below show the distribution of song syllables during early and late song development. Each dot represents one syllable, presenting the duration of that syllable versus its frequency modulation:

 

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Click here to download our Science article about dynamics of song imitation

Download a movie of syllable types emerging out of an amorphous cloud of undifferentiated sounds (30Mb)

 

How sleep affects song learning

 

As mentioned above, zebra finches sing about 1-2 million syllables over song development, or to be accurate, during the days of song development. What do they do over night? Sleep, of course.

But sleep is an active process, and it appears that vocal changes occur during sleep. Those changes are stronger, and qualitatively different than changes that occur during daytime singing.

 

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Click here to download our Nature article about how sleep affects song learning

 

Watch the NOVA Science Now episode about our research

 

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Watch the World Science Festival presentation about our research (mostly in part 3)

 

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Watch the BBC Horizon documentary about how birdsong and speech evolution might be linked

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Watch the PBS "The Music Instinct" documentary about our research

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