Figure 6: Effects of simulated cricothyroid contractions on phonation frequencies.

Different degrees of adduction of the thyroid (simulated contraction of cricothyroid muscle) on sound frequency caused frequency changes that were highly linear but limited to sounds emitted either within F₁^high or F₁^low. (a) Different degrees of adduction of the thyroid towards the cricoid cartilage (top panel), and (b) resulting changes in sound frequency. Air pressure was maintained constant at a level yielding sounds emitted at F₁^high. (c) Frequency changes for two preparations (pink dots and green squares, respectively; both from R. f. nippon) caused by adduction of the thyroid over a distance up to ~500 μm towards the cricoid cartilage (ten trials each). Pink dots depict same preparation as shown in a and b, and horizontal dashed line indicates the fundamental of the resting frequency (RF₁=34.8 kHz) for this animal obtained in vivo. Ranges of echolocation (Echol.)pulses and communication calls for this subspecies indicated at right (same data as in Fig. 3f).