Do nonlinear vocal phenomena signal negative valence or high emotion intensity?

Nonlinear vocal phenomena (NLPs) are commonly reported in animal calls and, increasingly, in human vocalizations. These perceptually harsh and chaotic voice features function to attract attention and convey urgency, but they may also signal aversive states. To test whether NLPs enhance the perception of negative affect or only signal high arousal, we added subharmonics, sidebands or deterministic chaos to 48 synthetic human nonverbal vocalizations of ambiguous valence: gasps of fright/surprise, moans of pain/pleasure, roars of frustration/achievement and screams of fear/delight. In playback experiments (N = 900 listeners), we compared their perceived valence and emotion intensity in positive or negative contexts or in the absence of any contextual cues. Primarily, NLPs increased the perceived aversiveness of vocalizations regardless of context. To a smaller extent, they also increased the perceived emotion intensity, particularly when the context was negative or absent. However, NLPs also enhanced the perceived intensity of roars of achievement, indicating that their effects can generalize to positive emotions. In sum, a harsh voice with NLPs strongly tips the balance towards negative emotions when a vocalization is ambiguous, but with sufficiently informative contextual cues, NLPs may be re-evaluated as expressions of intense positive affect, underlining the importance of context in nonverbal communication.

P2 L38-40. Pilot study. Was one synthetic sound build to match each of the 61 selected calls? P2 L40-41. How were long bouts truncated (was the end part cut out, or the beginning)? P2 L43. What is meant by '"unsuitable" ratings? P3 L42-43. 'The same images were shown in all trials in a block -that is, versions of the same prototype stimulus with and without NLPs were presented with the same (positive or negative) contextual cues'. This is not entirely clear. Do you mean that the same version of a stimulus with and without NLP was presented with the same image to one given participant? P5 L28 -P6 L10. It would help the reader if the rational behind each experiment (what information each of them brings) is explained briefly before describing the procedure, along with predictions.
Results. Throughout the results, what is regarded as no / moderate / strong effect? This could be specified beforehand in the method section. Different terms are used throughout the results (modest, marginal, small). It would be good to define how effect sizes are categorized. Also, could the WAIC results be added? (e.g. effect of the interaction between the main effectsjustifying why you then look at the effect of call type, measure and manipulation -> were these interactions present in the best selected model?)

Decision letter (RSOS-201306.R0)
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The submitted manuscript addresses this long-standing open problem -possible functions of nonlinear phenomena -in a creative and comprehensive way. The experimental design is done very carefully, the statistics (model selection, WAIC, ..) is appropriate, and the sample sizes are impressive. The authors use a carefully designed set of raw and modified vocalizations. They find as a starting point strong effects of the context on the valence but not on perceived intensity.The effects of nonlinear phenomena (NLPs) are less pronounced but thanks to large sample size and appropriate statistical analysis interesting conclusions could be drawn: listeners associate NLPs with aversive states and the context could even be changed from positive to negative. The exciting results expand our view on nonverbal communication and might even be a starting point to study possible functions of NLPs in non-human vocalizations.
Reviewer: 2 Comments to the Author(s) This paper investigates the effect of non-linear phenomena (NLP, in particular sub-harmonics and chaos), whose function is still debated. Indeed, they are usually assumed to be associated with an increase in negative arousal (e.g. fear), although when comparing between species, these features do not predictively increase with arousal. The three experiments conducted in this study nicely show that NLPs mainly increase the perceived aversiveness of vocalisations, in both negative and positive contexts, and only to a smaller extent, their perceived emotion intensity. Controlled synthetic sounds were used and the experiments and analyses seem correct to me. This paper would thus be a very valuable and nice addition to the literature of vocal expression of emotions.
I only have a few comments to improve the clarity of the manuscript: P2 L38-40. Pilot study. Was one synthetic sound build to match each of the 61 selected calls? P2 L40-41. How were long bouts truncated (was the end part cut out, or the beginning)? P2 L43. What is meant by '"unsuitable" ratings? P3 L42-43. 'The same images were shown in all trials in a block -that is, versions of the same prototype stimulus with and without NLPs were presented with the same (positive or negative) contextual cues'. This is not entirely clear. Do you mean that the same version of a stimulus with and without NLP was presented with the same image to one given participant? P5 L28 -P6 L10. It would help the reader if the rational behind each experiment (what information each of them brings) is explained briefly before describing the procedure, along with predictions.
Results. Throughout the results, what is regarded as no / moderate / strong effect? This could be specified beforehand in the method section. Different terms are used throughout the results (modest, marginal, small). It would be good to define how effect sizes are categorized. Also, could the WAIC results be added? (e.g. effect of the interaction between the main effectsjustifying why you then look at the effect of call type, measure and manipulation -> were these interactions present in the best selected model?)

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See Appendix A.
Decision letter (RSOS-201306.R1) We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.
Dear Dr Anikin, It is a pleasure to accept your manuscript entitled "Do nonlinear vocal phenomena signal negative valence or high emotion intensity?" in its current form for publication in Royal Society Open Science. The comments of the reviewer(s) who reviewed your manuscript are included at the foot of this letter.
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Please see the Royal Society Publishing guidance on how you may share your accepted author manuscript at https://royalsociety.org/journals/ethics-policies/media-embargo/. The 61 vocalisations in this pilot study were fully synthetic, but they were designed to be as similar as possible to the original recording and contained the same NLPs, if any.
R2_2 P2 L40-41. How were long bouts truncated (was the end part cut out, or the beginning)?
RESPONSE: The selection of stimuli was performed before the pilot experiment, which was designed to confirm that the chosen sounds were emotionally intense and ambiguous, so we felt justified in relying on intuition as well as previously collected data when making this initial selection. As a result, the sounds were selected and then synthesized without following formal criteria such as always taking the first or last x seconds, etc. For example, a 3.5 s roar of pain was synthesized to be shorter (1.2 s), while its intonation and voice quality were reproduced closely. Moans of pleasure in the original corpus often included long, multi-syllable bouts, in which case one or a few syllables were selected, regardless of their location in the bout (beginning, middle, or end). R2_3 P2 L43. What is meant by '"unsuitable" ratings?

RESPONSE: Changed to:
Based on the results of this pilot study, 13 out of 61 sounds were excluded because (a) participants often chose the "skip" option when rating them in either positive or negative scenarios, or (b) there was a large difference in intensity ratings between the positive and negative scenarios.
R2_4 P3 L42-43. 'The same images were shown in all trials in a block -that is, versions of the same prototype stimulus with and without NLPs were presented with the same (positive or negative) contextual cues'. This is not entirely clear. Do you mean that the same version of a stimulus with and without NLP was presented with the same image to one given participant? RESPONSE: For clarity, we changed the text to: Only the images shown in Table 2 were used, the same for all participants and in all trials in a blockthat is, versions of the same prototype stimulus with and without NLPs were presented with the same (positive or negative) contextual cues, enabling us to test the within-stimulus effect of acoustic manipulation in positive and negative contexts.