Effects of simultaneous perturbations of voice pitch and loudness feedback on voice F0 and amplitude control.

Perturbations in either voice pitch or loudness feedback lead to changes in a speaker's voice fundamental frequency (F0) or amplitude. Voice pitch or loudness perturbations were presented individually (either pitch or loudness shift stimuli) or simultaneously (pitch combined with loudness shift stimuli) to subjects sustaining a vowel to test the hypothesis that the mechanisms for these two response types are independent. For simultaneous perturbations, pitch and loudness both changed in the same direction or in opposite directions. Results showed that subjects responded with voice F0 or amplitude responses that opposed the direction of the respective pitch- or loudness shift stimuli. Thus, depending on the stimulus direction, both responses could either change in the same direction or in the opposite direction to each other. F0 response magnitudes were greatest with pitch-shift only stimuli (18 cents), smallest for loudness shift stimuli (10 cents) and intermediate with pitch combined with loudness shift stimuli (13 and 16 cents). Amplitude responses were largest with +3 dB stimuli (0.96 dB) and smallest with -3 dB stimuli (0.49 dB) but were not affected by the addition of pitch-shift stimuli. Results suggest the F0 and amplitude response mechanisms may be independent but interact in some conditions.