Figure 2

Direct gaze and disk or triangular stimuli attract the animals’ attention towards the center. (a) Plot of left target choice as function of the duration of a central stimulus, either a conspecific’s face looking straight at the observer (direct gaze) or a circular grey or black disk of similar size. Data pooled over the three animals (monkeys M1, M2, M3). A choice bias is evident at the shortest duration time, whereas for longer exposures the animals chose the targets on the right and left at random. Binomial probability: ***p < 0.001. (b) Bar plot of percentage of choices congruent with the darker half of a bipartite disk. Data pooled over the three animals (monkeys M1, M2, M3). For 100 ms presentation duration, the animals exhibited a significant preference for the target on the brighter side, i.e. opposite to the side preference to be expected based on a mechanism exploiting the luminance asymmetry associated with face orientation. At 300 ms the choices did not indicate a preference. Binomial probability: **p < 0.01; ***p < 0.001. (c) Bar plot of percentage of choices congruent with the side cued by the oriented triangles. Data pooled over the three animals (monkeys M1, M2, M3). No significant bias was detected.