Evolutionary derived modulations of attention to two common fear stimuli: serpents and hostile humans

In this paper we present an evolutionary analysis of attention to stimuli that are threatening from an evolutionary perspective, such as angry faces and snakes. We review data showing that angry, photographically depicted angry faces are more rapidly detected than happy faces in a visual search setting provided that they are male and that distractors are redundant in the sense that they are drawn from a small set of faces. Following Isbell's (2009) novel Snake Detection Theory, we predicted that snakes, as the prototypical predators, should be more rapidly detected than spiders, given that spiders have provided less of a predatory threat for primates. We review a series of experiments from our laboratory showing that snakes indeed are more rapidly detected than spiders provided that the target stimuli are presented in a demanding visual context, such as many distractor stimuli, or in peripheral vision. Furthermore, they are more distracting than spiders on the performance of a primary attention task. Because snakes were not affected by perceptual load, whereas spiders followed the usual rule of better detection with low perceptual load, we concluded that attending to snakes might constitute an evolutionary adaptation.