Several studies have shown that evolutionary relevant fear stimuli hold a privileged access to the fear module, an independent behavioral, psychophysiological and neural system that is automatically and selectively activated, and is relatively encapsulated from more advanced human cognition. However, to the best of our knowledge no study has yet directly assessed whether such stimuli are granted a facilitated access to visual awareness, compared to stimuli without such evolutionary relevance.

In the present study we used an interocular suppression technique, the Continuous Flash Suppression, known to reduce the activity along the geniculostriate pathway and to strongly suppress processing in the visual cortex.

Our goal was to investigate whether ecologically relevant fear stimuli (snakes and spiders) overcame suppression and accessed awareness to a larger extent than non-evolutionary relevant animal stimuli (birds).

Thirty university students volunteered to participate. Participants were asked to identify the screen quadrant in which the stimulus was presented in order to ensure that there was indeed a conscious processing.

The results confirmed our hypothesis by showing an advantage of fear stimuli (snakes and spiders) over the control stimulus (birds) in emerging from suppression into awareness, which was evidenced by significantly shorter response times.

Our findings support the notion that evolutionary relevant stimuli hold a privileged access into awareness, most likely involving a direct brainstem-thalamic route to the amygdala. Importantly, they contribute to elucidate the functions and mechanisms of the fear system and may have important implications for understanding emotional disorders, since many of these involve the fear system.

The authors have not supplied their declaration of competing interest.