Effect of formant frequency onset variation on the differentiation of synthesized /w/ and /r/ sounds

The purpose of this study was to assess the use of psychophysical transformations for analyzing the differentiation of /w/ and /r/ sounds of children and adults. Stimuli from Adult and Child manifolds, consisting of 25 synthesized /Cej/-type utterances with different F2 and F3 onset frequencies, were presented in random order to eight naive subjects. Subjects rated the stimuli on a four-point scale between good /r/ and good /w/. Correlations between mel transformations and Bark transformations of the F3-F2 differences among the stimuli and their percent /r/ responses were close to or greater than .90. Predictions of percent /r/ responses derived from regression analyses based on mel transformations and Bark transformations of F3-F2 differences among stimuli indicated that some sounds identified as /w/ for /r/ substitutions could be differentiated from /w/ sounds. The category boundaries between /r/ and /w/ were estimated to be 5.0 Bark for adult stimuli and 5.7 Bark for child stimuli.