chimpanzee social experiment

Performance was not better than chance, however, for vocalizations of copulation (having sex) (t = −2.99, p = 0.003,d = 0.17, 95% CIs (−0.04, 0.003)), being separated from mother (t = 2.81, p = 0.005,d = 0.16, 95% CIs (0.04, 0.23)), being tickled (t = 1.77, p = 0.19,d = 0.10, 95% CIs (−0.01, 0.19)), and discovering something scary (t = −16.49, p = 0.003,d = 0.93, 95% CIs (−0.68, −0.53)). Thus, listeners might need additional contextual information to be able to specify vocalizations produced in certain type of contexts, or might not be able to identify certain contexts from vocalizations at all. Therefore, the focus of Experiment 3 was manipulating the physical proximity of the social partner to the focal chimpanzee during the accumulation test, and making the outcome of the task contingent on the social partner. Vocalizations with higher arousal levels were longer in duration compared to vocalizations with lower arousal levels. All acoustic parameters, SCoG (χ92=92.919, p < 0.001), duration (χ92=114.154, p < 0.001), f0 mean (χ92=92.283, p < 0.001), f0 s.d. Multinomial logistic regressions (MLR) were performed in SPSS (Version 23, IBM Statistics) on the acoustic features to determine whether the acoustic parameters provide sufficient information to predict the actual behavioural contexts and arousal levels, and binomial logistic regression (BLR) for valence. A power analysis (G*Power 3.1; [20]) based on a t-test given d = 0.2, power = 0.80, α = 0.05 showed that 156 judgments per stimulus were needed. We predicted that listeners would be able to categorize the behavioural contexts and to judge the arousal level and valence from the vocalizations at better-than-chance levels. ), selecting from yes and no options. Here we report the results of experiments involving 13 adult females who formed 11 different dyads. After the practice and screening trials, each participant was randomly assigned to one of the 10 conditions, each focusing on a specific behavioural context. and D.A.S. http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The results were very clear: chimpanzees preferably chose to provide food to both themselves and their partner – but only if it was the partner that had made this choice possible. We declare we have no competing interests.

(Note. In experiment 2, we therefore sought to test whether listeners would be able to match vocalizations to behavioural contexts in a simpler task involving a single behavioural context for each participant. are supported by ERC Starting grant no. In the analysis comparing listeners' performance for vocalizations produced in negative versus positive contexts, the judgements of behavioural contexts were not employed, as participants were unable to identify any of the contexts at better-than-chance levels. For each context, vocalizations were obtained from between 4 and 21 individual chimpanzees.). On arrival at the laboratory, each participant was led to a silent individual cubicle. The animals were particularly generous if their partners had risked obtaining no food for themselves at all by providing their assistance. However, previous studies are limited to domesticated animals that are distantly related to humans. The results show that participants were not able to accurately categorize any of the behavioural contexts (ps > 0.005, Bonferroni corrected; figure 1a). To ensure that the study was not underpowered, data were collected from 14 additional participants to allow for potential exclusions (see Statistical analyses for exclusion criteria). Judgments were more accurate for negative as compared to positive vocalizations. In line with our findings, Maruščáková and colleagues [11] found that simple acoustic features such as pitch were more useful in human judgments of valence than noisiness in piglet vocalizations. Such tasks are difficult for listeners as it is more challenging to evaluate and compare contexts [4]. )Download figureOpen in new tabDownload powerPoint, Figure 3. Researchers of TCP in the Taï National Park work closely with the Wild Chimpanzee Foundation and the Ivorian national park authorities (OIPR - Office Ivorien des Parcs et Réserves) to protect the chimpanzees' future. Participants were given two screening questions. This suggests that some main motivations for human cooperation might have been present in our common ancestor already while supporting findings from game theory. Specifically, performance was significantly better than chance for eating high value food (t = 5.04, p < 0.001,d = 0.28, 95% confidence intervals (CIs) (0.15, 0.34)), eating low value food (t = 9.59, p < 0.001,d = 0.55, 95% CIs (0.49, 0.75)), discovering a large food source (t = 5.52, p < 0.001,d = 0.31, 95% CIs (0.17, 0.37)), being refused access to food (t = 13.09, p < 0.001,d = 0.74, 95% CIs (0.63, 0.85)), being attacked by another chimpanzee (t = 22.99, p < 0.001,d = 1.29, 95% CIs (1.06, 1.26)), and threatening an aggressive chimp or predator (t = 11.19, p < 0.001,d = 0.64, 95% CIs (0.37, 0.53)). The power analysis was conducted based on the context categorization task, as we expected it to be the most difficult for participants. Accuracy levels for matching vocalizations produced in negative contexts were significantly better than those from positive contexts (negative: M = 0.43, s.d. As part of the hygienic protocol staff go through three days of quarantine in the North camp before moving to the research camps. = 0.89) and representative vocalizations (M = 2.14, s.d. Having a permanent vet on site and using a field laboratory we are able to monitor the health status of staff and wildlife. We measured acoustic features of 155 vocalizations produced by 66 individual chimpanzees using PRAAT [25]. of fundamental frequency (f0) and harmonics-to-noise ratio (HNR). After completing two practice trials, participants listened to the 155 chimpanzee vocalizations and for each were asked to (i) make a forced-choice context categorization, selecting from 10 categories, (ii) indicate the level of arousal on a 5-point scale (1 = very low, 5 = very high, and (iii) indicate the emotional valence on a 5-point scale (1 = very negative, 5 = very positive).

“The findings suggest that the chimpanzees take into account not only the actions of their test partners but also their cooperative intentions, and that they can differentiate truly prosocial behaviour from potentially self-serving acts,” says Sebastian Grüneisen, another of the study’s authors. Specifically, decreases in this parameter (corresponding approximately to less pitch variability) predicted better listener accuracy in identification of arousal levels. The sample size was predetermined by a power analysis using G*Power 3.1 [20] for a t-test given d = 0.2, power = 0.80, α = 0.005. This contradicts the common assumption that chimpanzees only care for themselves as soon as a chance for more food is involved,” says Martin Schmelz, one of the study’s authors. <<<]eva.mpg.de, © 2020, Max Planck Institute for Evolutionary Anthropology, Leipzig, Great Ape Evolutionary Ecology and Conservation, Robert Koch Institute (Fabian Leendertz, Project Group Zoonoses, OIPR - Office Ivorien des Parcs et Réserves, Centre Suisse de Recherches Scientifiques en Côte d'Ivoire, Centre Suisse de Recherches Scientifique (CSRS), Abidjan, Cote d’Ivoire, LANADA, Labo Veterinaire Central, Bingerville, Cote d'Ivoire, Office Ivorien des Parces et Reserves (OIPR), Cote d’Ivoire, Wild Chimpanzee Foundation (WCF), West African Office, Abidjan, Cote d’Ivoire, Cultural differences between neighboring communities, Angela Friederici, MPI for Cognition and Brain Sciences, Leipzig, GER. To assess the effect of different degrees of acoustic regularities in vocalizations on perception of behavioural contexts from heterospecific vocalizations, future studies should aim at including vocalizations from multiple species differing in phylogenetic closeness. Experiment 1 (project no. On average, participants rated both behavioural contexts (M = 1.86, s.d. In order to test our hypothesis that human listeners would perform better than chance in matching vocalizations to context types, d-prime scores for each participant were tested against chance (random guessing, reflected by a d-prime score of zero) using separate one sample t-tests for each context type at the Bonferroni-corrected level α level (α= 0.005). It has been suggested that even though increasing the number of alternatives in forced-choice tasks has advantages (e.g. First, we examined whether behavioural context, arousal level, and valence would be reflected in the acoustic structure of the vocalizations. All reported having no hearing impairments and no experience working with or studying chimpanzees.

They are social creatures, whose pass their life in the company of their peers. We therefore employed paired sample Wilcoxon signed-rank tests. The 10-way context categorization task used in experiment 1 was challenging for participants because they were asked to choose from a substantial number of unfamiliar behavioural context categories.

Listeners failed to match vocalizations of copulation, being separated from mother, being tickled and discovering something scary.

Drawing on two complementary approaches to phylogenetic continuity in emotional expressions, we sought to test the hypotheses that (i) human listeners can accurately infer the type of behavioural context in which chimpanzee vocalizations were produced [16]; and that (ii) human listeners can correctly judge arousal and valence from chimpanzee vocalizations [12]. = 0.37, positive: M = 0.22, s.d. To assess how accurately human listeners judged the arousal level and valence of the vocalizations, ratings on the 5-point scales were transformed into −2 (very low), −1 (low), 0 (medium), 1 (high), 2 (very high); and −2 (very negative), −1 (negative), 0 (neutral), 1 (positive), 2 (very positive). This continuity may allow humans to accurately infer affective information from vocalizations produced by chimpanzees. ), Vocal expression of emotions in mammals: mechanisms of production and evidence, Hear them roar: a comparison of black-capped chickadee (, Humans rely on the same rules to assess emotional valence and intensity in conspecific and dog vocalizations, Humans recognize emotional arousal in vocalizations across all classes of terrestrial vertebrates: evidence for acoustic universals, Humans identify negative (but not positive) arousal in silver fox vocalizations: implications for the adaptive value of interspecific eavesdropping, Human behavioural discrimination of human, chimpanzee and macaque affective vocalisations is reflected by the neural response in the superior temporal sulcus. Duration (χ62=8.789, p < 0.01), f0 mean (χ62=19.797, p < 0.01) and HNR mean (χ62=5.381, p < 0.05) made significant unique contributions. Perceptual mechanisms may exist that allow human listeners to infer richer affective information from particular types of behaviours than inferences of core valence [16]. : 21.05; time of the maximum peak frequency: 4.10) indicating that there was a collinearity problem [31]. Following this transformation, all variables were checked for normality using a Shapiro–Wilk test, which indicated that they were not normally distributed (ps < 0.001).

Bold indicates better than the chance level performance. In experiment 1, listeners (n = 310), categorized the vocalizations in a forced-choice task with 10 response options, and rated arousal and valence.

: 1.25; HNR mean: 1.56; HNR max: 1.62). Because we tested 10 behavioural contexts, the total sample size was set to 3120. For instance, listeners correctly identified arousal levels in silver fox vocalizations only when they were produced in negative contexts [8].

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