Nasal temperature change in response to conspecific screams in chimpanzees as measured by a thermal infrared camera

抄録

The interplay between emotion and cognition is one of the key areas in primatology that is likely to grow substantially in the coming years. A crucial component for this to happen hinges on the development of reliable methods to measure emotion in primates both at the physiological and behavioral levels. Previous studies have used thermal imaging (measured by an infrared thermal camera) to investigate lie detection in human adults, embarrassment and irritation in children, and fear in macaques. Here we established the conditions and techniques needed to apply the same method to great apes. In experiment 1, in Germany, 9 chimpanzees were tested in 3 conditions in which they heard, respectively: conspecific screams (experimental), an orangutan' long call (control 1), and no sound (control 2). We measured facial temperature right before and after the playbacks. Chimpanzees dropped their nasal temperature in response to conspecific screams, but not in the control conditions. In experiment 2, in Japan, 3 chimpanzees were additionally tested under the same conditions, yet in this experiment, the facial temperature could be measured in an environment with fewer distractions and consequently, we were able to obtain measurements before/after as well as during the playbacks. In addition, we also measured the heart rate of one of the chimpanzees. We replicated and extended the results from experiment 1. In summary, changes in facial temperature could be reliably detected in chimpanzees hearing conspecific screams after a relatively short period of time since the stimulus onset (< 30 sec.). However, the influence of general activity (walking, eating) was not negligible, which means that such artifacts need to be carefully controlled to obtain reliable measures of emotion based on facial temperature.