section_path: Causes
section_name: Causes
paragraph_text: Causes
  
  An influential categorization of stimuli causing fear was proposed by psychologist Jeffrey Alan Gray; namely, intensity, novelty, special evolutionary dangers, stimuli arising during social interaction, and conditioned stimuli. Another categorization was proposed by Archer, who, besides conditioned fear stimuli, categorized fear-evoking (as well as aggression -evoking) stimuli into three groups; namely, pain, novelty, and frustration, although he also described " looming ", which refers to an object rapidly moving towards the visual sensors of a subject, and can be categorized as "intensity". Russell described a more functional categorization of fear-evoking stimuli, in which for instance novelty is a variable affecting more than one category: 1) Predator stimuli (including movement, suddenness, proximity, but also learned and innate predator stimuli); 2) Physical environmental dangers (including intensity and heights); 3) Stimuli associated with increased risk of predation and other dangers (including novelty, openness, illumination, and being alone); 4) Stimuli stemming from conspecifics (including novelty, movement, and spacing behavior); 5) Species-predictable fear stimuli and experience (special evolutionary dangers); and 6) Fear stimuli that are not species predictable (conditioned fear stimuli).