Early in my teaching career I kept a captive born squirrel monkey in a classroom laboratory along with a variety of lizards and snakes. Once the monkey realized snakes were present, it would scream, race back and forth in its cage and literally bounce off-the-walls in a display that was impossible to ignore. After seeing the snakes the monkey respond with the same display towards completely harmless objects that were snake-shaped, like ropes and garden hoses. Research over the past 20 years has suggested humans have evolved the ability to detect snakes as a threat – an attentional bias – that has served to warn humans of a snake’s presence before it has an opportunity to bite. This mechanism involves fear of snakes as well as a visual sensitivity to objects shaped like snakes, most likely a detection mechanisms similar to the ones found in monkeys.
Vanessa Lobue, of Rutgers University, and Judy Deloache, at the University of Virginia, have recently published the results of a series of experiments using touch screen technology with preschool children and adults. The subjects were presented with 3x3 matrices of color photographs and asked to touch a target on the screen as quickly as possible. Based on previous research, parallel results were expected for the adult and the preschool participants; they expected adults would respond more rapidly than the children, but that the two age groups would display the same pattern of performance. The subjects responded to snakes much more rapidly than frogs as expected. In one experiment they found the color of the snake was not important in detection; but other experimental sets suggest recognizing a coiled object (coiled snake vs. a coiled wire vs. flower); the coiled snake and coiled wire were detected more rapidly than the flower. But the differences between detecting the snake and detecting the wire were not statistically significant. In another experimental set and one using a snake stretched out, the coiled snake was detected more rapidly.
It seems likely that human fear as well as human obsession with snakes have an evolutionary origin and will keep psychologists busy for sometime trying to understand the impact of snakes on the human brain.
Lobue, V. and J. S. Deloache. 2011. What's so special about slithering serpents? Children and adults rapidly detect snakes based on their simple features. Visual Cognition, 19(1):129-143