Pourtois et al. found that when participants were asked to judge the placement of the bar, they were significantly better at judging the orientation when it replaced the fearful compared to the neutral face. Therefore it can be concluded that humans have evolved a type of attentional bias towards fearful stimuli, hence detect fearful expressions faster than neutral. This attentional bias can be classed as a survival instinct as vital information, such as when a threat (predator) is approaching can be passed more efficiently from one group member to the other, increasing the likelihood of survival (Ohman, 2001). .
Furthermore, research suggests humans subconsciously process biological cues portrayed by the eyes of others, helping them detect emotions. Whalen et al. (2004) used photographs of fearful and happy eyes for the experiment, yet removed all other information except for pupils and the sclera of the eyes. During the experiment, whilst the different eyes were being presented to each participant (presented too quickly for conscious awareness of the stimuli), amygdala activation was significantly enhanced when participants were presented with fearful eyes compared to happy. The amygdala is primarily involved in attention, emotion and learning whilst it also constantly assess potential dangers, hence controlling emotionally significant events and the fight or flight response (Adams et al., 2003). Whalen et al. concluded that the ratio of pupil to sclera visible to others indicates an immediate and unconscious measure of either safety or danger: with a larger ratio being perceived as danger. This finding portrays biological evidence for the efficient detection of fear. .
Additionally, there is evidence suggesting that threatening faces themselves are detected faster than other expressions. Hansen and Hansen (1988) investigated the, "face in the crowd effect," and presented participants with angry, happy or neutral faces within their 3 experiments.