Fig. 6

Predicted changes in vowel quality of animal calls depending on the context, relative to an unarticulated schwa vowel [ə]. Based on what we know about sound symbolism in human vocalizations and speech, and recent research on vocal strategies for size exaggeration or intimidation [124, 125], we predict that formant spacing corresponding to [i]-like vowels in vocalizations should be optimal for conveying submission or friendly intentions (sounding small and harmless), whereas [a] should be optimal for long-distance or aggressive calls, and [u] for size exaggeration