Do snakes alter our visual attention to food?

Abstract

The need to detect and avoid predators drives many aspects of foraging behavior. Snakes are historical predators of primates, but predator avoidance-foraging tradeoffs are rarely studied in humans. We examined whether humans have a detection bias for snake versus food images using eye-tracking technology in 76 undergraduate student participants (38 men, 38 women). We tested three questions: 1) Do humans exhibit a visual bias to snakes over food? 2) Does food palatability affect any visual bias to snakes? 3) Is the response to snakes specific for these predators or a generalized reaction to a visually evocative stimulus? We analyzed three metrics in balanced pairs of food and snake images and images normatively ranked for arousal (low, high) and emotional valence (negative and positive): saccade latency, gaze duration, and saccade bouts. There was a strong bias toward shorter saccade latency with the snake images relative to food images. Gaze duration and saccade bouts were significantly greater for snake images relative to food images. Food palatability had discrete effects on the visual bias to snake images. Finally, qualitatively similar effects on visual bias were observed in response to negative valence, high arousal non-snake images. While humans display a gaze bias to snakes over food, this bias may be related to the negative valence and high arousal linked to snake images rather than key visual features of snakes themselves.