Fig. 2

Rat fUSVs are produced with adducted vocal folds. A Above a threshold tracheal flow V, the isolated larynx produces fUSVs. From top to bottom: tracheal mass flow V, received sound pressure (black line, RMS), sound spectrogram (NFFT = 2048, overlap = 50%, Hamming window), and scaled Shannon’s entropy with the 0.7 threshold for USV detection indicated. Dark green, time binned signal; light green, smoothed signal. B With abducted vocal folds and open membranous glottis only 1 larynx produced fUSVs (left), while with adducted, opposed vocal folds all larynges (N = 10) produced USVs (right) and within the in vivo frequency range of 18–96 kHz [32]. Different colors represent different individuals. Boxplots indicate median, 25th and 75th percentiles and whiskers extend to most extreme data points excluding outliers. For raw data, see Table 1