Judgement of the Vowel Colour of Natural and Artificial Sounds

Five vowel sounds, each produced in five different ways, were presented to subjects with widely differing experience of tasks of this type for identification.

The vowels were the last five of the standard set of eight cardinal vowels, and were presented to subjects with no experience of phonetics as belonging to the words bat, bart, bought, boat and boot. Each vowel was (a) spoken by a phonetician, (b) synthesized by adding individual harmonics in direct imitation of the spoken sounds, (c) represented by two pure tone components only, (d) synthesized by a talking machine (P.A.T.) and (e) imitated by selecting harmonics with a low-pass filter.

All these sounds were categorised more or less “correctly” by skilled subjects; and, although there were wide and systematic differences in accuracy with untrained subjects, these performed consistently better than chance.

The experiment showed (a) that the selection of harmonics according to formant theory is not the only, and perhaps not always the best means of synthesizing isolated vowels, (b) that even sounds which are poor representations of vowels can still be categorised with some consistency even by untrained subjects and (c) that a simple “percent correct” score is less sensitive than other measures.