Trypophobia - a fear of (clusters of small) holes - was first formally described by Geoff G. Cole and Arnold J. Wilkins in their paper for Psychological Science August 2013 entitled
“The image most often reported as inducing the phobia is the seed head of the lotus flower. Other examples include soap bubbles and the holes in aerated chocolate.”
The team were the first to document a seemingly innate aversion that many people have to (images of) groups of small holes. In their tests, 11% of males and 18% of females reported unpleasant reactions to the images.
The evolutionary reasons why such feelings have arisen with regard to images of clusters of small holes are presently unknown. The original paper suggested that the images might have similar contrast profiles (i.e. comparatively high contrast energy at midrange spatial frequencies) to images of dangerous animals - but other images with similar contrast patterns do not appear to produce such effects.
A subsequent set of experiments, reported in 2018, determined that the unpleasant reactions to images of holes was more associated with 'disgust' than with 'fear'. See: Pupillometry reveals the physiological underpinnings of the aversion to holes in PeerJ 6:e4185, January 4, 2018.
Again there is no currently agreed explanation for the aversion.
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