Noise-Induced Frequency Modifications of Tamarin Vocalizations: Implications for Noise Compensation in Nonhuman Primates

<div><p>Previous research suggests that nonhuman primates have limited flexibility in the frequency content of their vocalizations, particularly when compared to human speech. Consistent with this notion, several nonhuman primate species have demonstrated noise-induced changes in call amplitude and duration, with no evidence of changes to spectral content. This experiment used broad- and narrow-band noise playbacks to investigate the vocal control of two call types produced by cotton-top tamarins (<i>Saguinus Oedipus</i>). In ‘combination long calls’ (CLCs), peak fundamental frequency and the distribution of energy between low and high frequency harmonics (<i>spectral tilt</i>) changed in response to increased noise amplitude and bandwidth. In chirps, peak and maximum components of the fundamental frequency increased with increasing noise level, with no changes to spectral tilt. Other modifications included the Lombard effect and increases in chirp duration. These results provide the first evidence for noise-induced frequency changes in nonhuman primate vocalizations and suggest that future investigations of vocal plasticity in primates should include spectral parameters.</p></div

ANOVA results for the diel analysis of both sites.

<p>ANOVA results for the diel analysis of both sites.</p

Diagram of experimental setup.

<p>Letters indicate equipment placement; M = microphone; C = video camera; NS = speaker presenting noise stimulus; ES = speaker presenting elicitation stimulus.</p

Representative CLCs produced by subject Mulva during a) control and b) treatment A trials illustrating changes to spectral tilt.

<p>All whistles from a) have strong fundamental frequencies and maximum energy in the 2^nd harmonic, while in b) the first whistle has a very faint fundamental frequency at approximately 2 kHz, and peak frequencies for all whistles occur in the 4^th harmonics. Reduced energy in the fundamental frequency is also apparent in the second and third whistles (spectrogram parameters: 1024 point Hamming window, 75% overlap, 11.7 Hz frequency resolution).</p

Spectrogram of a gunshot sound recorded in Roseway West.

<p>Spectrogram parameters: 2 kHz sampling, Hann window, discrete Fourier transform (DFT) size 128, analysis resolution  = 15.6 Hz and 0.032 s, 50% overlap.</p

Locations of autonomous recording units on the Scotian Shelf.

<p>Roseway West: 42°58′00″ N 65°03′24″W; Emerald South: 43°8′54″N 62°45′42″W. Numbers correspond to water depth in meters.</p

Seasonal trends of gunshot signal production.

<p>The hours per day with gunshots (GS) showed a seasonal pattern in both Roseway West (top) and Emerald South (bottom). In Roseway West, August-November had significantly more gunshot presence than other months. Emerald South, despite having fewer hours per day with gunshots overall, still exhibits a seasonal trend, with significantly more gunshot hours during the second half of the year.</p

Spectrograms of CLC (a) and chirp (b) vocalizations with measured frequency characteristics indicated.

<p>This CLC consists of one chirp and four whistle syllables. All measurements of CLCs were made on the call as a whole and the individual syllables within the call (not shown); measurements of chirps were made from the fundamental frequency (first harmonic). Note that peak frequency measurements for all syllables, fundamental frequencies, and whole calls were taken automatically from the selection spectrum view in Raven 1.4 (not shown).</p

Noise stimuli.

<p>Spectrograms (1024 point Hamming window, 75% overlap, 11.7 Hz frequency resolution) of noise playback stimuli recorded during trials. Treatments A–C had a bandwidth of 5 kHz. Treatments D–F had a 10 kHz bandwidth. Harmonic structure is due to frequency response of the playback system.</p

ANOVA results for the seasonality analysis of both sites.

<p>ANOVA results for the seasonality analysis of both sites.</p