title: Who is afraid of the invisible snake? Subjective visual awareness modulates posterior brain activity for evolutionarily threatening stimuli.
abstract: Snakes were probably one of the earliest predators of primates, and snake images produce specific behavioral and electrophysiological reactions in humans. Pictures of snakes evoke enhanced activity over the occipital cortex, indexed by the "early posterior negativity" (EPN), as compared with pictures of other dangerous or non-dangerous animals. The present study investigated the possibility that the response to snake images is independent from visual awareness. The observers watched images of threatening and non-threatening animals presented in random order during rapid serial visual presentation. Four different masking conditions were used to manipulate awareness of the images. Electrophysiological results showed that the EPN was larger for snake images than for the other images employed in the unmasked condition. However, the difference disappeared when awareness of the stimuli decreased. Behavioral results on the effects of awareness did not show any advantage for snake images.
authors.affiliation: Department of Psychology, University of Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, Finland. Electronic address: simone.grassini@utu.fi.
authors.forename: Simone
authors.initials: S
authors.lastname: Grassini
authors.affiliation: Department of Psychology, University of Turku, Finland.
authors.forename: Suvi K
authors.initials: SK
authors.lastname: Holm
authors.affiliation: Department of Psychology, University of Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, Finland.
authors.forename: Henry
authors.initials: H
authors.lastname: Railo
authors.affiliation: Department of Psychology, University of Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Koivisto
mesh_terms: D000328:Adult; D000818:Animals; D001364:Awareness / Q000502:physiology*; D001921:Brain / Q000502:physiology; D005239:Fear / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology; D010698:Phobic Disorders / Q000503:physiopathology; D010775:Photic Stimulation / Q000379:methods*; D012911:Snakes; D013334:Students / Q000523:psychology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Awareness; Consciousness; Early posterior negativity (EPN); Evolution; Snake detection hypothesis; Snake fear; Spider fear; Visual masking