Page 92 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 4
Experiment 1: Examining biased attention to emotions in bonobos
Method
Participants
Our sample included four bonobos (Besede [12 yo], Kumbuka [18 yo], Monyama [7 yo], and Zuani [~16 yo]; all female) that are part of a social group of 12 individuals housed in the primate park Apenheul, Apeldoorn, The Netherlands. Except for Zuani, all bonobos took part in two prior touchscreen studies (Kret et al., 2016). At time of testing, none of the bonobos were pregnant nor were on contraceptives. During winter time (from November to the end of March), the park is closed for visitors, allowing us to conduct experimental research. All but one individual (Zuani) were born and raised in captivity. During non-testing hours, the bonobos had access to a 2812m2 outdoor and 158m2 indoor enclosure, and testing took place in the indoor enclosure.
The zoo kept the bonobos separated into two groups that varied in group composition on a weekly basis to mimic naturalistic fission-fusion dynamics. During testing periods, only one group of the bonobos was given access to the test apparatus. For ethical reasons, the group was never split further. This meant that when one individual was tested, its group members were present nearby. Water was available ad libitum, and food (a variety of vegetables, fruits, and branches and leaves) was provided four to five times a day, as well as nutritionally balanced mash.
Tests with the bonobos followed the EAZA Ex situ Program (EEP) guidelines, formulated by the European Association of Zoos and Aquaria (EAZA). Bonobos voluntarily participated in the experiment and were never restrained or forced to take part. Furthermore, only positive reinforcement (juice) was used during training and testing, and juice was also offered to the bonobos that did not take part in the experiment. Data were collected between February 2017 – March 2017, and December 2017 – April 2018.
Equipment
Our setup is comparable to those in other research facilities (see Hopper et al., 2020), and involves one PC running Tobii Studio (v.3.4.8), two computer screens (one for the experimenter, one for the participant, 1280x1024 pixels), a webcam to record the bonobos while they were tested, and a Tobii X2-60 eye tracker mounted on one of the screens. One computer screen, together with the eye
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