Page 161 - Demo

Eye-tracking reveals bias to flanges in orang-utans1597we used the great ape eye tracking mode on the eye tracker. On the top of the screen, we added a webcam to record the participants during the test sessions.First, we calibrated the participants using a resizing video as a calibration target in Tobii Pro Lab. We used a range of different videos during the calibration process, depicting caretakers, baby orang-utans, food, and mating orangutans. The calibration process was repeated until a successful calibration was obtained, and this calibration was reused during the experiment. With Sandy, we managed to obtain a successful 5-point calibration, whereas the other orangutans completed a successful 2-point calibration, which is sufficient to produce accurate gaze data for this type of experimental design (Hopper et al., 2021). After the calibration phase, data collection began. Each participant completed nine sessions of six trials (54 trials in total). Each session started with a 9-point grid to visually inspect calibration accuracy. Thereafter, six trials were started. Each trial started with a fixation video in the center of the screen (180 × 180 pixels) depicting one of the orang-utan caretakers. Stimulus presentation was started manually; when the eyetracker showed that the participant’s gaze overlapped with the fixation video, the experimenter proceeded to the stimuli, which were presented for four seconds. After the stimulus presentation, a gray screen was shown for three seconds. After all six trials were completed, the experiment was automatically stopped. Participants completed a maximum of three sessions on testing days, and the order of the sessions was randomized between participants.After the participants had completed all nine sessions, we repeated trials in which the participant (i) looked away from the center during trial onset because the start point of the trial would not be neutral, or (ii) showed less than 1s of fixation time on the stimuli during the trial because this could indicate a lack of attention and/or distraction during the trial. During the experiment, the orangutans were rewarded with strongly diluted (±1:35) sugar-free raspberry lemonade.StimuliIn each trial, two stimuli, 690 × 500 pixels each, were presented: one flanged face and one unflanged face on a light-gray background (#808080). The stimuli were centered at 20% and 80% horizontally and 50% vertically on a dark-gray background (#626262). The stimuli were collected from the Internet, mainly from release reports published by Bornean orang-utan reintroduction programs. These were supplemented with portrait pictures taken from semi-wild orang-utans and pictures of zoo-housed orang-utans within the orang-utan EEP. Tom Roth.indd 159 08-01-2024 10:41