Page 50 - Summer 2018

Speech: Not So Acoustic
subtle bits of information as soon as the sound arrives at the ear. For example, when hearing “The man has drunk the ...,” an observer will look at an empty glass but instead will look at a full glass when hearing “the man will drink the...” (Alt- mann and Kamide, 2007). These actions make sense when you stop and think about the meaning of the words, but no such deliberate reckoning is needed because the eye gaze shifts are rapid and occur much earlier than the subsequent words like “water” or whatever else should finish the utter- ance. This is yet another example of how perception of a word (“water”) is not just about receiving the acoustic pres- sure waves but can also be shaped dramatically by factors that have nothing to do with the acoustics of the word itself.
Prediction of upcoming words is not merely a neat trick that emerges in the laboratory; it is the foundational principle of entire frameworks of speech perception theories (see Lupy- an and Clark, 2015). It is why individuals can complete our friends’ and spouses’ sentences and why one can expect a big play when a sports announcer’s voice begins to swell with ex- citement. Brain-imaging studies have validated the idea of speech perception as a process of continual prediction and er- ror correction rather than a straightforward encoding of the incoming signal. Skipper (2014) shows that there is actually metabolic savings afforded by the use of context, contrary to the idea that computing context is a costly extra processing layer on top of auditory sensation. He goes on to say that the majority of what we “hear” during real-world conversation might come not from our ears but from our brain.
Conclusion
The study of speech acoustics has demanded creativity and collaboration among a variety of experts spanning multiple fields of study, including acoustics and beyond. There is so much literature on the topic that it is easy to lose track of a reality that is perhaps more obvious to a person who does not study speech communication: speech is not nearly as acoustic as one might think. Speech has been and will con- tinue to be driven in large part by studies of the sounds of the vocal tract and the auditory-perceptual mechanisms in the ear that encode those sounds. It is undeniable that the quality of the speech signal itself plays a large role in our per- ception; just ask anyone who has hearing loss. However, by recognizing the nonacoustic factors involved in speech per- ception, one might better understand why computers don’t recognize speech as well as humans; despite hyperspeed de- tailed analysis of the acoustic signal, only part of the infor- mation is in the signal, and the rest lies elsewhere, either in the environment, on the face of the talker, in the statistics of the language, or, more likely, in the mind of the listener.
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