Measuring structure of speech and animal signals with lossy compression


One-line summary
Measure structure of animal calls with an MP3-like compressor that works for any animal

Research question:
How can we measure the structure of speech and animal signals in such a way that we can compare the level of organization?

Human speech is unique in that it uses a small set of basic speech sounds and recombines them into an unlimited number of utterances. Interestingly, the basic set of speech sounds and the rules for combining them are different for every language. Humans can learn this effortlessly, but no other animal appears to be able to do this (Yip, 2006).

The proposed project is part of a larger project to understand what cognitive mechanisms have evolved to deal with learning complex speech. Part of the project consists of building learning computer models to investigate from the bottom up what mechanisms are needed to solve the problem of learning speech.

Outline of the project:

The proposed project consists of implementing a model that can measure the entropy rate of a stream of symbols. The entropy rate of a signal can be approximated by how well it can be compressed.  Lossless data compression algorithms are no good as we are dealing with a continuous, noisy signal and we therefore need to separate meaningless noise from meaningful variation, and for this we need to take properties of hearing and cognition into account. In a sense, we try to build an MP3-like compression system in which we can plug known properties of animal hearing (properties of hearing are different for each animal, so even though MP3 works for humans, it may not work for other animals).

Comparing information rates human speech and animal signals has been attempted before (e. g. Doyle et al., 2011)but the signals were always divided into building blocks by human observers. The contribution of this project will be that it will work with the original signals directly. The measure will then be applied to the different sets of signals, and a statistical analysis of their degree of structure needs to be done.

The student:

I am looking for a student who wants to do some serious programming, but who is also able to design and run an experiment with the model, as well as to collect and pre-process data from internet sources. As the basic questions have to do with human speech and animal communication, an interest in these topics is important as well.


  • Doyle, L. R., McCowan, B., Johnston, S., & Hanser, S. F. (2011). Information theory, animal communication, and the search for extraterrestrial intelligence. Acta Astronautica, 68, 406-417.
  • Yip, M. J. (2006). The search for phonology in other species. Trends in cognitive sciences, 10(10), 442-446.

Please contact Bart de Boer if you are interested in this project.