Fig. 2. Spectrograms of pup calls modified in temporal and frequency domains and used in playback experiments to mothers. (A) Low-pass; (B) high-pass; (C) fundamental frequency and its first two harmonics (FundFreq+H1+H2); (D) fundamental frequency and only the first harmonic (FundFreq+H1); (E) fundamental frequency only (FundFreq); (F) filter of every third harmonic (1H/3); (G) filter of every second harmonic (1H/2); (H) with time-reversed frequency modulation (FM); (I) without amplitude modulation (AM); (J) natural call (control). Each colour represents an amplitude class of 3 dB. Oscillograms for I and J are also shown.
