Ever since ?hman, Flykt and Esteves published their classic study in 2001, many researchers have replicated their findings regarding attentional bias to threatening stimuli in visual perception research. Based on these findings, psychologists proposed a promising theory called predatory fear, in which the attentional bias to threatening animals is interpreted as evolutionarily adaptive behavior of early mammals and the ancestors of modern humans. However, from an evolutionary perspective, the lack of ecological validity of existing experiments inevitably attenuated the interpretation. The present study aimed to fill the gaps by repeating the classic work in a virtual reality environment.
A virtual reality grove was created with the Virtools virtual reality engine, in which jungles, trees, flowers, and weeds were arranged in the form of a wild grass field. The virtual reality grove was presented with an Oculus Rift DK 2 helmet. Forty participants were instructed to navigate along a path in the grove and search for threatening or non-threatening target stimuli. 3D models of a snake, a spider, a flower, a mushroom, a cicada, and a squirrel were used as stimuli in the search task, among which snake and spider were considered threatening stimuli. All the stimuli were shown in yellow and were assessed by twenty participants not included in the forty participants in search task to ensure they were of similar salience.
To examine attentional bias to threatening stimuli, two experiments were conducted in the same visual search task as reported by ?hman et al. In Experiment 1, as in ?hman et al., the snake or the spider was selected as a target stimulus, and thirteen copies of the flower or the mushroom were used as distracting stimuli, or other combinations of these. Twenty participants were individually presented with the virtual grove and instructed to passively wander along the path in the jungle to search for target stimuli. A fixed camera was set at a uniform speed to simulate the navigation in visual search task. Given that searching for animals took less time than searching for plants ( Soares et al, 2009), flowers and mushrooms were replaced with cicadas and squirrels in Experiment 2. The other twenty participants repeated the experiment procedure. In addition to response time (RT), response distance (RD) was also computed as a compensatory index.
In Experiment 1, the results of RTs revealed that the searching for threatening stimuli (snake and spider) is faster than searching for non-threatening stimuli (mushroom, flower). The RD values showed that participants found the threatening stimuli when they were farther away than the non-threatening stimuli. In Experiment 2, the same results were found even when the distracting stimuli were all animals. The RTs and RDs both confirmed that participants were better at finding snakes and spiders than finding flowers, mushrooms, cicadas, and squirrels.
The total results supported the hypothesis of predatory fear was relatively soundly and the attentional bias to threatening animals, especially snake and spider, was found to be likely to be caused by predatory fear as part of human cognition. These findings provide new evidence for the hypothesis of predatory fear from an evolutionary perspective. In addition, virtual reality was proven to be a suitable technique for assessing the ecological validity of psychological experiments.