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3 How Does the Brain Represent Speech?
OIWI PARKER JONES1 AND JAN W. H. SCHNUPP2
1 University of Oxford, United Kingdom
2 City University of Hong Kong, Hong Kong
Introduction
In this chapter, we provide a brief overview of how the brain’s auditory system represents speech. The topic is vast, many decades of research on the subject have generated several books’ worth of insight into this fascinating question, and getting close up and personal with this subject matter necessitates a fair bit of background knowledge about neuroanatomy and physiology, as well as acoustics and linguistic sciences. Providing a reasonably comprehensive overview of the topic that is accessible to a wide readership, within a short chapter, is a near‐impossible task, and we apologize in advance for the shortcomings that this chapter will inevitably have. With these caveats and without further ado, let us jump right in and begin by examining the question What is there to ‘represent’ in a speech signal?
The word representation is quite widely used in sensory neuroscience, but it is rarely clearly defined. A neural representation tends to refer to the manner in which neural activity patterns encode or process some key aspects of the sensory world. Of course, if we want to understand how the brain listens to speech, then grasping how neural activity in early stages of the nervous system encodes speech sounds is really only a very small part of what we would ideally like to understand. It is a necessary first step that leaves many interesting questions unanswered, as you can easily appreciate if you consider that fairly simple technological devices such as telephone lines are able to represent speech with patterns of electrical activity, but these devices tell us relatively little about what it means for a brain to hear speech. Phone lines merely have to capture enough of the physical parameters of an acoustic waveform to allow the resynthesis of a sufficiently similar acoustic waveform to facilitate comprehension by another person at the other end of the line. Brains, in contrast, don’t just deliver signals to a mind at the other end of the line, but they have to make the mind at the other end of the line, and to do that they have to try to learn something from the speech signal about who speaks, where they might be, what mood they are in, and, most importantly, the ideas the speaker is trying to communicate. Consequently it would be nice to know how the brain represents not just the acoustics, but also the phonetic, prosodic, and semantic features of the speech it hears.
Readers of this volume are likely to be well aware that extracting
