Patterns on serpentine shapes elicit visual attention in marmosets (Callithrix jacchus)

Given the prevalence of threatening snakes in the evolutionary history, and modern-day environments of human and nonhuman primates, sensory, and perceptual abilities that allow for quick detection of, and appropriate response to snakes are likely to have evolved. Many studies have demonstrated that primates recognize snakes faster than other stimuli, and it is suggested that the unique serpentine shape is responsible for its quick detection. However, there are many nonthreatening serpentine shapes in the environment (e.g., vines) that are not threatening; therefore, other cues must be used to distinguish threatening from benign serpentine objects. In two experiments, we systematically evaluated how common marmosets (Callithrix jacchus) visually attend to specific snake-like features. In the first experiment, we examined if skin pattern is a cue that elicits increased visual inspection of serpentine shapes by measuring the amount of time the marmosets looked into a blind before, during, and after presentation of clay models with and without patterns. The marmosets spent the most time looking at the objects, both serpentine and triangle, that were etched with scales, suggesting that something may be uniquely salient about scales in evoking attention. In contrast, they showed relatively little interest in the unpatterned serpentine and control (a triangle) stimuli. In experiment 2, we replicated and extended the results of experiment 1 by adding additional stimulus conditions. We found that patterns on a serpentine shape generated more inspection than those same patterns on a triangle shape. We were unable to confirm that a scaled pattern is unique in its ability to elicit visual interest; the scaled models elicited similar looking times as line and star patterns. Our data provide a foundation for future research to examine how snakes are detected and identified by primates. Am. J. Primatol. 78:928-936, 2016. © 2016 Wiley Periodicals, Inc.