Page 162 - Demo

Chapter 7160We checked for differences in luminance and contrast between stimuli using a custom MATLAB script to determine luminance and contrast for each stimulus, and then calculated the difference in luminance and contrast between the flanged and unflanged stimuli at the trial level. We found no robust differences in contrast (Bayesian intercept-only LM; 89% CrI [-0.08; 0.35], pd = 0.85) or luminance (Bayesian intercept-only LM; 89% CrI [-0.23; 0.21], pd = 0.53) between flanged and unflanged stimuli. This check ensured that gazing patterns were not driven mainly by low-level features at the stimulus level, which are known to capture visual attention (Theeuwes, 1995).Experiment 2ProcedureThis procedure was identical to that used in Experiment 1. However, because of time pressure, we applied a maximum of four sessions per participant per test day instead of three. Experiment 2 consisted of 12 sessions of six trials in total, followed by repetition of erroneous trials, similar to Experiment 1.StimuliOwing to an editing mistake, the dimensions of the stimuli for Experiment 2 were slightly different from those in Experiment 1. Each trial consisted of two stimuli of 600 × 450 pixels, centered at 22.5% and 77.5% horizontally and 50% vertically on a dark-grey background (#626262). While this meant that Experiments 1 and 2 were slightly different, the presentation of stimuli was administered in exactly the same way as in Experiment 2.For Experiment 2, we selected six naturalistic stimuli of four different orangutan males (two flanged: Bako & Sibu, two unflanged: Jingga & Wousan). Stimuli of Bako and Jingga were provided by Ouwehands Zoo (Rhenen, The Netherlands), stimuli of Sibu were provided by Dublin Zoo (Dublin, Ireland), and stimuli of Wousan (housed in Paignton Zoo, UK) were kindly shared by Brian Lilly. All four males were part of the orang-utan EEP and had not been previously housed with the subjects of the study. We selected four portrait photos and two photos depicting both the face and (part of the) body. Using GIMP (v2.10.32), we transformed each photo to grayscale and then applied the Equalize-option to standardise the luminance of all stimuli. We paired the stimuli such that participants were always presented with stimuli from the same category within Tom Roth.indd 160 08-01-2024 10:41