Attention to social stimuli is modulated by sex and exposure time in tufted capuchin monkeys

The dot-probe task is an experimental procedure commonly used to study how animals (including humans) pay attention to different stimuli. In this study, we evaluated how different durations of image exposure modulate the response to this task and how male and female tufted capuchin monkeys (Sapajus spp.) respond to different social stimuli. Subjects were shown pairs of images of unfamiliar conspecifics: a male vs. a female or two individuals grooming vs. two individuals not engaged in grooming. With shorter image exposures (250 ms) both sexes responded faster to (i.e., biased their attention towards) images of unfamiliar males compared to females, and were unaffected by images of grooming compared to nongrooming. With longer image exposures (1000 ms) females biased their attention towards images of unfamiliar females, while males did not show any difference; in contrast, males biased their attention towards images of grooming compared to nongrooming, while females did not show any difference. We interpret these results as showing that responses to the dot-probe task with different image exposures reflect different attentional phenomena, and that the two sexes differ in how social stimuli affect their attention.