278 Erik R. Thomas, Norman J. Lass, and Jeannine Carpenter
by African Americans were identi¿ ed more accurately than those uttered by
European Americans. Additionally, the strength of each of these trends var-
ies for each listener group, with the African American listeners showing the
strongest effects for each independent variable. Accuracy rates overall were
quite high, rising to over 96% for stimuli with diagnostic vowels identi¿ ed by
North Carolina European Americans. The fact that identi¿ cation rates were
well over 80% regardless of what kind of stimulus was involved suggests that
factors other than vowel quality and prosody were being accessed by listen-
ers. The most likely candidates for other cues are voice quality features, such
as phonation.
Interactions of independent variables were important in two cases. Figure
12.2 shows the interaction of presence/absence of diagnostic vowels with nat-
ural/swapped prosody. Here, the two North Carolina listener groups behaved
Figure 12.1 Results of Experiment B for each independent variable.