Fear of snakes
has been documented in some primates as well as humans, and snake-phobia is
regarded as a global phenomenon. Lynn
Isbell’s study of the human visual system proposes that some aspects of it
evolved to facilitate the detection of snakes. Evidence to support her argument
included a series of investigations that showed that human adults have an
attentional bias for the detection of fear-relevant stimuli such as snakes when
compared to neutral stimuli such as flowers and mushrooms. Other recent studies
suggest that preschool children, 8- to 14-months old infants, and even
non-human primates also detect snakes more quickly than neutral stimuli such as
flowers. Nobuo Masataka and colleagues performed an experiment with 74 children
3- to 4-years old and adults. The test subjects were asked to find a single
target black-and-white photo of a snake among an array of eight black-and-white
photos of flowers as distracters. As target stimuli, the researchers prepared
two groups of snake photos, one set in which a typical striking posture was
displayed by a snake and the other in which a resting snake was shown. Masataka
and colleagues then measured the reaction time to find the snake photo. This
was then compared between the resting and striking snakes. The reaction time to
find the striking snake had a mean value significantly faster for the photos of
snakes displaying a striking posture than for the photos of resting snakes in
both the adults and children. These findings suggest the possibility that the
human perceptual bias for snakes per se could be differentiated according to
the difference of the degree to which their presence acts as a fear-relevant
stimulus.
 |
| Masataka et al. Figure 2. An example of a 363 matrix used as the stimulus in an experimental trial where a photo of striking posture of a snake was included (Striking), and one where a photo of a resting snake was included (Resting). From doi:10.1371/journal.pone.0015122.g002 | | | |
 |
| Masataka et al. Figure 3. Mean reaction time to detect a snake when striking posture was displayed in the target photo and when a resting snake was shown in the target photo. From doi:10.1371/journal.pone.0015122.g003 |
Literature
Isbell, L. A.
2009. The Fruit, the Tree, and the
Serpent: Why We See So Well. Cambridge: Harvard University Press.
Masataka, N., S.
Hayakawa, and N. Kawai. 2010. Human Young Children as well as Adults
Demonstrate ‘Superior’ Rapid Snake Detection When Typical Striking Posture Is
Displayed by the Snake. PLoS ONE
5(11): e15122. doi:10.1371/journal.pone.0015122
Labels: human evolution, snake phobia
