Methodology of Experiments on the Perception of Synthesized Vowels

A method of checking the reference frames of listeners during experiments concerned with the perception of synthetic vowels has been evaluated. The checking was achieved by interpersing standard vowels in a sequence of experimental vowels. It was found that the responses to the standard vowels were substantially independent of the quality of the experimental vowels with which they were included. Most of the listeners, however, were unable to distinguish more than about six categories of standard vowels, so small shifts in their reference frames were difficult to detect.