KeywordsSpeech Signal Vocal Tract Speech Sound Hard Palate Acoustic Method
Phonetics is the study of human vocal sounds, and linguistic phonetics is the study of those sounds that are used in speech. Some authors use the term “phonetics” to refer only to the study of speech sounds, but the study of nonspeech vocal sounds such as infant cries, coughs, and singing can employ many of the same methods as are used in linguistic phonetics even though speech per se is not involved.
There are many aspects to the study of phonetics, but three main ways of investigating it are by using perceptual methods, acoustic methods, or instrumentation. Perceptual methods involve the auditory analysis of speech or vocal sounds, using either live or recorded stimuli. Since much research concerns the intelligibility, comprehensibility, or other type of impression of the vocal sound on another human, perceptual methods are considered the most ecologically valid. However, the human speech perceptual system is noted for its biases, many gained through experience with speech. These biases help humans filter extraneous information from the speech signal and extract just the information that will be useful for making quick decisions about what is being communicated. However, information which is “extraneous” in this sense is often scientifically useful, so acoustic methods are often paired with perceptual ones to provide a fuller picture of the speech signal.
Acoustic research in phonetics incorporates knowledge of normal and disordered vocal tract physiology, mathematical acoustics, signal processing, and perceptual psychophysics. Recordings of vocalizations are digitally processed (generally using an algorithm of the Fourier transform) and displayed on a computer screen in the form of a spectrogram, which is a graph showing the changes in frequency and amplitude of the utterance over time. From this, visual-perceptual analyses can be performed, along with quantitative measurements of frequency and amplitude at various points in the utterance.
Other instrumentation is also used in phonetic research. For example, a palatometer shows where the tongue contacts the hard palate during speech production. A nasometer measures airflow through the nasal passages during speech. X-ray videography and electropalatography give views of how the articulators of speech (lips, tongue, palate, velum, pharynx, and others) move during utterances. More recently, facial movements involved in speech have been studied using reflective dots and motion-sensitive cameras.
In order to standardize the representation of speech sounds across languages, the International Phonetic Association (IPA) has devised an alphabet used to phonetically transcribe normal and disordered speech.
References and Reading
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