Some of this is my opinion rather than consensus, but in case you’re interested:
I believe that the human brainstem (superior colliculus) has an innate detector of certain specific visual things including slithering-like-a-snake and scuttling-like-a-spider, and when it detects those things, it executes an “orienting reaction” which involves not only eye-motion and head-turns but also conscious attention, and it also induces physiological arousal (elevated heart-rate etc.). That physiological arousal is not itself fear—obviously we experience physiological arousal in lots of situations that are not fear, like excitement, anger, etc.—but the arousal and attention does set up a situation in which a fear-response can be very easily learned. (Various brain learning algorithms are also doing various other things in the meantime, such that adults can wind up with that innate response getting routinely suppressed.)
My experience is that stairs don’t trigger fear-of-heights too much because you’re not looking straight down off a precipice. Also, I think sufficiently young babies don’t have fear-of-heights? I forget.
I’m not making any grand point here, just chatting.
Some of this is my opinion rather than consensus, but in case you’re interested:
I believe that the human brainstem (superior colliculus) has an innate detector of certain specific visual things including slithering-like-a-snake and scuttling-like-a-spider, and when it detects those things, it executes an “orienting reaction” which involves not only eye-motion and head-turns but also conscious attention, and it also induces physiological arousal (elevated heart-rate etc.). That physiological arousal is not itself fear—obviously we experience physiological arousal in lots of situations that are not fear, like excitement, anger, etc.—but the arousal and attention does set up a situation in which a fear-response can be very easily learned. (Various brain learning algorithms are also doing various other things in the meantime, such that adults can wind up with that innate response getting routinely suppressed.)
My experience is that stairs don’t trigger fear-of-heights too much because you’re not looking straight down off a precipice. Also, I think sufficiently young babies don’t have fear-of-heights? I forget.
I’m not making any grand point here, just chatting.