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General discussion2119explore sexually selective cognition in Bornean orang-utans by employing similar test paradigms that have been used to study this topic in humans. However, I was able to employ these paradigms only with mixed success. Based on my experiences, future studies could consider improving their approach in several ways. In the section above, I already argued for a more biocentric approach to animal cognition (Bräuer et al., 2020). Taking such a perspective is essential to ensure that tasks are valid measures of the hypothesized cognitive processes involved in performing the task (Schubiger et al., 2020). I want to elaborate on this in the context of Chapter 6, where I tested Bornean orang-utans in two touchscreen tasks, that both yielded null results. First, Bornean orang-utans have historically been exposed to extremely long periods of food scarcity (Vogel et al., 2017). As a consequence, orang-utans are extremely well-equipped to saving energy. For example, orang-utans have very low levels of daily energy expenditure compared to other mammals (Pontzer et al., 2010) and will minimise travel costs by adapting their locomotion style (Roth et al., 2017; Thorpe et al., 2007). Whereas sensitivity to food rewards has not been systematically studied yet, it is to be expected that Bornean orangutans are extremely sensitive to and focused on food rewards. This is also what I noticed in the touchscreen task. At the end of each trial, individuals would receive a reward, in order to keep them motivated. However, it sometimes seemed that the anticipation of a reward distracted them from the task. More specifically, although they performed the task correctly, they showed little involvement in it, and seemed more focused on the reward. Such a finding is not unique to orangutans, however. In quantity judgment tasks, primates are well-known to show improved performance when they need to discriminate between abstract tokens instead of actual food items (e.g., Boysen & Berntson, 1995). This suggests that primates are naturally inclined to respond to rewarding stimuli, which might disrupt their ability to focus on and complete tasks effectively. Interestingly, I did not encounter the same problem during the eye-tracking experiment (Chapter 7), where individuals received a reward continuously throughout the trial. This design might have avoided continuous anticipation of reward, thereby increasing involvement in the task. Therefore, I consider studies that can provide a reward to orang-utans while they are performing a test trial more likely to be successful.Second, the touchscreen setup employed in Chapter 6 allowed orang-utans to only use their hands during the tasks. However, manual tasks may not be the most suitable tasks for orang-utans, as they often seem to employ their mouth Tom Roth.indd 211 08-01-2024 10:42