Page 133 - Demo

Absence of cognitive bias to flanges in orang-utans1316receiving the participant’s attention, they will first need to switch their attention to the dot before they can indicate the location. Thus, if the dot appears behind a stimulus that immediately attracts attention, participants will be faster to respond than when the dot appears behind a less salient stimulus (van Rooijen et al., 2017). Recently, the dot-probe task has been used to study emotion perception in different primate species (orang-utans: Laméris et al., 2022; chimpanzees: Kret et al., 2018; Wilson & Tomonaga, 2018; rhesus macaques: King et al., 2012; Lacreuse et al., 2013). In addition, the task has successfully been used in humans to study attractiveness bias (Ma et al., 2019; Ma, Zhao, et al., 2015; Roth et al., 2022). In general, these studies have established that individuals immediately attend to evolutionarily relevant stimuli, such as emotional expressions or preferred partners. Therefore, we here employed the dot-probe task to study direct attention towards sexually relevant facial characteristics in orang-utans.When it comes to choice bias, Watson et al. (2012) developed a paradigm to test choice biases in unrestrained primates. In this task, individuals first learn to associate two coloured dots (red and green) with specific categories (e.g., pictures of faces), so that they can predict what they will see on the screen by clicking a specific dot. During the test phase they can choose between the two coloured dots: both choices yield the same reward, but the picture that will appear on the screen is different. The authors successfully used this method to study preference for sex and status in rhesus macaques: they found that rhesus macaques chose to look more at faces of dominant males and perinea of conspecifics, while they were less likely to choose pictures of low-ranking conspecifics. Because this task has been successfully applied to rhesus macaques, here we used an adapted version to study choice bias for flanges in orang-utans.The present paper reports the results of two studies. These two studies aimed to investigate direct attentional biases towards flanged and symmetrical faces, and a choice bias for flanged faces in Bornean orang-utans, respectively. Given that the presence of flanges or facial symmetry may be a signal of good genes, we predicted for the dot-probe task that individuals should respond faster on trials where the dot would replace stimuli that depicted males with large flanges or males with symmetrical faces than when the dot replaced stimuli that depicted males with small or no flanges or asymmetrical faces. For the choice task, we expected individuals to more often choose the coloured dot that was associated with pictures of flanged males over the coloured dot that was associated with unflanged males. Tom Roth.indd 131 08-01-2024 10:41