Bats distress vocalizations carry fast amplitude modulations that could represent an acoustic correlate of roughness

Abstract

communication sounds are ubiquitous in the animal kingdom, where they play a role in advertising physiological states and/or socio-contextual scenarios. Human screams, for example, are typically uttered in fearful contexts and they have a distinctive feature termed as "roughness", which depicts amplitude fluctuations at rates from 30-150 Hz. In this article, we report that the occurrence of fast acoustic periodicities in harsh sounding vocalizations is not unique to humans. A roughness-like structure is also present in vocalizations emitted by bats (species Carollia perspicillata) in distressful contexts. We report that 47.7% of distress calls produced by bats carry amplitude fluctuations at rates ~1.7 kHz (>10 times faster than temporal modulations found in human screams). In bats, rough-like vocalizations entrain brain potentials and are more effective in accelerating the bats' heart rate than slow amplitude modulated sounds. our results are consistent with a putative role of fast amplitude modulations (roughness in humans) for grabbing the listeners attention in situations in which the emitter is in distressful, potentially dangerous, contexts.

Male Carollia perspicillata bats call more than females in a distressful context

“…The classifier ( fitcsvm function, rbf kernel, no standardization) was trained using 100 vocalizations, of which 50 had pronounced periodicities in the 1.1-2.5 kHz according to their TMS and 50 which did not have them. These vocalizations have been used for the same purpose in another study [25] and were picked randomly from the original dataset after visual inspection.…”

“…In C. perspicillata, periodicity values are more than 10 times faster than in humans (approx. 1.7 kHz) and have been proposed as the parameter that renders bat vocalizations rough or harsh [25]. This characteristic is common in distress calls [30,31] and makes them easier to localize [32].…”

“…We classified the distress syllables into fast amplitude modulated (fAM) and non-fAM vocalizations, using a binary support vector machine classification algorithm. As a training set, we used vocalizations (50 fAM and 50 non-fAM) from another dataset [25]. Note the peak at approximately 1.7 kHz for the fAM calls in the TMS (figure 1e).…”

“…The emission pattern and neuronal processing of distress calls emitted by C. perspicillata have been investigated in previous studies [10,23,24]. This bat species emits distress sequences temporally arranged into syllable groups (bouts) [10] and individual syllables carry amplitude fluctuations at rates of approximately 1.7 kHz that could represent an acoustic correlate of perceptual roughness [25]. None of the previous studies on distress calling in C. perspicillata explored possible sex differences in calling patterns.…”

Acoustic context modulates natural sound discrimination in auditory cortex through frequency specific adaptation

“…While listening to echolocation signals indicates the presence of a navigating conspecific, hearing a distress call indicates the presence of an individual under duress and thus a potentially harmful situation. In bats, distress sounds have strong communicative power and they trigger autonomic (Hechavarria et al ., 2020) and hormonal responses in the listeners (Mariappan et al ., 2016). Navigation and distress sounds differ markedly not only in their ethological value but also in their acoustic attributes, especially in their frequency composition with distress energy peaking at ~23 kHz and echolocation peaking at frequencies above 60 kHz (Hechavarria et al ., 2016).…”