What is the objective of this study?

It is crucial for the survival of animals that group members recognize each other’s emotional expressions and produce adequate emotional responses. The bonobo is the closest living human relative, together with the chimpanzee. Researching emotions from our ancestors can provide insight in the evolutionary nature of human emotions. Bonobos can show consolatory, appropriate behaviours after conflict and they are effective in self-regulation. The current study researches the emotional attention of the bonobo. Emotional attention can be measured using reaction times with the dot-probe test. Bonobos have rich and emotional lives and a soft and friendly character. The objective of this study is to see whether bonobos are similar in performance on the dot-probe task to humans. People are biased towards images in this task, especially threatening images. The researchers want to know if Bonobos display the same attentional bias and which emotional behaviour attracts the most attention.

What is the method used in this study?

Four female bonobos completed the dot-probe task. During the task, emotional and neutral pictures of unknown bonobos were shown. The reaction times of the bonobos was measured before they tapped on the image on the touch screen that followed an emotional image. The same exercise was repeated using affiliative and protective behaviours in the images. Nose wipes were also measured as a sign of negative emotion. The researchers tested whether nose wipes occurred more frequently in emotional trials than neutral ones. To measure positive emotions of the bonobos, pictures were taken during the test and shown to experts from Apenheul.

What are the results of this study?

According to the results, bonobos attention was biased towards the location of the emotional, not the neutral scene. Their attention was more focused on images that showed conspecifics, including sexual behaviour, but also yawning or grooming. Bonobos showed less signs of distress and aggression with viewing these images. This suggests that the bonobo society also has protective and affiliative behaviour, and this causes the immediate attraction of attention. The application of a well-known human paradigm to investigate apes showed that apes show increased attention towards emotional stimuli, compared to neutral ones. It also shows they are mostly drawn toward affiliative and protective emotions. No significant effect was found for the occurrence of nose wipes.

What did the researchers conclude?

Observations have shown that bonobos are very social and can use their emotions to resolve or avoid conflict. Bonobos have, like humans, an increased attention for group members’ and their own emotions. This is the first study that found evidence for the heightened attention for emotional versus neutral cues in bonobos. According to the results the researchers proposed the following statements about their study:

1. The bonobos that were experimentally tested showed the most attention towards pictures of yawning bonobos. There is an ongoing debate on the function of yawning, but it has social significance. Yawning is supposed to cool down the brain, yawing induces vigilance, which is evolutionary adaptive behaviour often picked up by other members of a group. The involvement of a mirror neuron system while contagious yawning takes place shows contagious yawning is based on empathy.
2. It could be that bonobos displayed threat when shown images of canines (a less threatening chimpanzee). It is unlikely because these images did not draw more attention of the bonobos.
3. Touch is used for the display of social emotions and affection. Especially grooming is very important, not only socially, but also in terms of hygiene and its calming effects. It is no surprise bonobos respond strongly to the grooming images.
4. The increased attention towards sexual images versus neutral images can be explained by the high frequency and importance of sex in the bonobo’s life.
5. The attention of a bonobos is quickly captured by the emotional expression of others. The strongest response is with affiliative behaviours such as mating and grooming, but also highly contagious behaviour such as yawning. This suggests that affiliative behaviours are pivotal in bonobo society and therefore prioritized.

Summary: Bonobos (pan paniscus) show an attentional bias toward conspecifics’ emotions

• The objective of this study is to see whether bonobos are similar in performance on the dot-probe task to humans. People are biased towards images in this task, especially threatening images. The researchers want to know if Bonobos display the same attentional bias and which emotional behaviour attracts the most attention.
• According to the results, bonobos attention was biased towards the location of the emotional, not the neutral scene. Their attention was more focused on images that showed conspecifics, including sexual behaviour, but also yawning or grooming. Bonobos showed less signs of distress and aggression with viewing these images.

Study note: Bonobos (pan paniscus) show an attentional bias toward conspecifics’ emotions

• Can you think about reasons for studying emotional behaviour in primates from an evolutionary perspective on emotions?
• Which parts of the emotional responses in bonobos are similar to human emotions?