Page 52 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 2
of the photo participant and outside of the view of the dot-probe participant. Photos were taken on the same spot near the test location, around the corner and against a background with a brick wall. The participant was asked to express one of each of the four emotions (angry, fearful, happy, sad), based on an example from Model 1 from the NimStim database (Tottenham et al., 2009) printed on a sheet of paper. After each emotional expression, the participant was asked to show a neutral expression. This prevented the use of the same neutral photo across all trials, and ensured some variation in the neutral expressions. As such, eight unique photos were taken (four emotional, four neutral). Low quality photos were retaken on the spot.
Next, the pictures were loaded into the software (which automatically handled the resizing of stimuli) and the dot-probe participant was then seated behind the touchscreen. The experimenter entered personal data (age, handedness, sex of both the dot-probe and photo participant, the nature of their relationship, and how often they see each other (Table S9). The instructions for the task were kept to a minimum, as the bonobos could also not receive written or verbal instructions.
The experimenter told the participant that they would see a dot appear on the screen, and that they would have to touch the dot as soon as it appeared by using only their dominant hand. The task started with the pictures of the four bonobos participating in Experiment 1, with the text “Are you faster than the bonobos? Press anywhere on the screen to continue”. After three practice trials that included pictures of flowers, the participants saw a display asking them whether they understood the task and were reminded of using only one hand during the task. Participants could then move on to the experiment by pressing the red dot on the screen. The experimental procedure was similar to that in Experiments 1 and 2 with bonobos. A trial started with a start dot in the lower middle part of the screen. Upon touching the start dot, two stimuli were presented side by side for 300 ms. These stimuli were an emotional and neutral stimulus of either a familiar companion or an unfamiliar individual. A probe then replaced one of the stimuli. After touching the probe, a blank screen was shown for 2000 ms, after which the next trial would start. After completing all 40 trials, participants would see a screen depicting their average reaction time and how it compared to that of the bonobos. The location of the stimuli on the screen (left/right) and the location of the probe were counterbalanced, and stimuli were presented in a randomized order. The whole procedure took about 15 to 20 minutes to complete.
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