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Absence of cognitive bias to flanges in orang-utans1476paradigm, while we expected a bias towards larger flanges and more symmetrical faces. With regard to flanges, previous research has shown that orang-utans spend a substantial amount of time looking at flanges while scanning male faces (Kano et al., 2012). However, it is possible that the manipulation we used, which involved presenting faces with slightly larger or smaller flanges, did not generate salient enough differences between the stimuli to produce robust variations in reaction times. Therefore, future research could repeat the approach with different combinations of flanged and unflanged males instead. Regarding symmetry, we recently reported a similar null result in humans in the exact same task (Roth et al., 2022): human participants had no attentional bias towards symmetrical faces. While the aforementioned explanation of too little difference in salience between stimuli would also apply to our null results in the current study, there is also an important theoretical consideration. While previous literature has often emphasised the importance of symmetry for mate choice (Gangestad et al., 1994; Møller & Thornhill, 1998), recent literature has criticised this notion in humans on the basis that the link between symmetry and attractiveness seems overstated (Jones & Jaeger, 2019)and the link between symmetry and health remains equivocal (Pound et al., 2014). Thus, while our null findings could be the result of methodological limitations, the results for facial symmetry are in accordance with recent null findings and theoretical debates in humans.Moreover, the experimental paradigm that we used to study immediate attention, the dot-probe paradigm, has been subject to debate in humans due to its relatively poor reliability (Kappenman et al., 2014; Rodebaugh et al., 2016). Similarly, some inconsistent results have been observed when applying this paradigm to primates. While the paradigm has successfully shed light on the influence of emotion information on cognition in various primate species (King et al., 2012; Kret et al., 2016; Lacreuse et al., 2013; Schino et al., 2020; van Berlo et al., 2023), inconsistencies persist. For example, we have recently shown that Bornean orang-utans do not seem to show the expected attentional bias towards emotions in the dot-probe task (Laméris et al., 2022). This raises the question of whether such a widely reported bias is genuinely absent in Bornean orang-utans or if the current paradigm fails to capture it adequately. One potential methodological reason for these inconsistencies is that the dot-probe paradigm relies on reaction times, which are inherently noisy (Morís Fernández & Vadillo, 2020). Especially for species with relatively low levels of manual dexterity compared to humans, such as orang-utans (Bardo et al., 2017), reaction time might not be the most suitable Tom Roth.indd 147 08-01-2024 10:41