Trypophobia: The fear of holes

Abstract

Phobias are usually described as an irrational and persistent fear of certain objects or situations, and causes of such fears are difficult to identify. We describe an unusual but common phobia (trypophobia), hitherto unreported in the scientific literature, in which sufferers are averse to images of holes. We performed a spectral analysis on a variety of images that induce trypophobia and found that the stimuli had a spectral composition typically associated with uncomfortable visual images, namely high contrast energy at midrange spatial frequencies. Critically, we found that a range of potentially dangerous animals
also possess this spectral characteristic. We argue that although sufferers are not conscious of the association, the phobia arises in part because the inducing stimuli share basic visual characteristics with those of dangerous organisms, characteristics that are low-level, easily
computed, and therefore facilitate a rapid non-conscious response.

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Psychological Science
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DOI: 10.1177/0956797613484937
published online 27 August 2013Psychological Science
Geoff G. Cole and Arnold J. Wilkins
Fear of Holes
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DOI: 10.1177/0956797613484937
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Research Article
According to the fourth edition of the Diagnostic and
Statistical Manual of Mental Disorders (American
Psychiatric Association, 2000), a phobia can be defined as
a marked and persistent fear of a specific object or situa-
tion that invariably provokes anxiety. Furthermore, the
individual may recognize that the fear is excessive and
unreasonable. Although setting out criteria for such aver-
sions is relatively easy, identifying the etiology of the fear
is difficult. Indeed, isolating cause has been one of the
main challenges of phobia research. For instance, there
have been accounts of phobia based on evolutionary
principles (Marks & Nesse, 1994), classical conditioning
(e.g., Merckelbach & Muris, 1997), and the role of
thoughts and beliefs about objects and situations (e.g.,
Hertel & Brozovich, 2010).
Such theories of phobia acquisition can have difficulty
explaining many phobias. A case in point, and central to
this article, is trypophobia—the fear of holes. Sufferers
report aversion to visual stimuli comprising particular
configurations of holes. The stimuli are usually clusters of
holes of any variety that are almost always innocuous
and seemingly pose no threat. Although no peer-reviewed
articles currently exist concerning the phenomenon, its
documentation on the Internet surpasses that of several
more widely recognized phobias, and there are a number
of Internet-based support groups, including a Facebook
site (https://www.facebook.com/groups/3318322299/),
where people provide testimonials. It is clear from these
accounts that for many people, trypophobia affects their
everyday lives and can be quite debilitating. For instance,
one sufferer reported, “[I] can’t really face small, irregu-
larly or asymmetrically placed holes, they make me like,
throw up in my mouth, cry a little bit, and shake all over,
deeply.” The image most often reported as inducing the
phobia is the seed head of the lotus flower (see Fig. 1).
Other examples include soap bubbles and the holes in
aerated chocolate. To obtain an initial estimate of how
common trypophobia is, we asked 286 adults (91 male
and 195 female; age range = approximately 18–55 years)
to view an image of the lotus seed head. The participants
indicated whether the image was “uncomfortable or even
repulsive to look at.” Ten males (11%) and 36 females
(18%) reported aversion.
484937PSSXXX10.1177/0956797613484937Cole, WilkinsFear of Holes
research-article2013
Corresponding Author:
Arnold J. Wilkins, Centre for Brain Science, University of Essex,
Wivenhoe Park, Colchester CO4 3SQ, England
E-mail: arnold@essex.ac.uk
Fear of Holes
Geoff G. Cole and Arnold J. Wilkins
Centre for Brain Science, University of Essex
Abstract
Phobias are usually described as irrational and persistent fears of certain objects or situations, and causes of such
fears are difficult to identify. We describe an unusual but common phobia (trypophobia), hitherto unreported in the
scientific literature, in which sufferers are averse to images of holes. We performed a spectral analysis on a variety
of images that induce trypophobia and found that the stimuli had a spectral composition typically associated with
uncomfortable visual images, namely, high-contrast energy at midrange spatial frequencies. Critically, we found that
a range of potentially dangerous animals also possess this spectral characteristic. We argue that although sufferers are
not conscious of the association, the phobia arises in part because the inducing stimuli share basic visual characteristics
with dangerous organisms, characteristics that are low level and easily computed, and therefore facilitate a rapid
nonconscious response.
Keywords
phobia, trypophobia, holes, evolution, visual stress, aposematism, threat, fear, evolutionary psychology, vision,
avoidance
Received 7/3/12; Revision accepted 2/19/13
Psychological Science OnlineFirst, published on August 27, 2013 as doi:10.1177/0956797613484937
by Anna Mikulak on September 3, 2013pss.sagepub.comDownloaded from

2 Cole, Wilkins
Sufferers of trypophobia report that it is the visual per-
cept that is particularly aversive. This aversion can be
contrasted with, for instance, an aversion to cats, in which
a person with ailurophobia will be uncomfortable in the
presence of a cat even if it is not visible. Furthermore,
trypophobia seems to increase if the holes occur on
human skin. It is only in this respect that the phobia
involves any reference to the semantics of the image. The
visual nature of trypophobia provides a clue as to its
cause.
For many years, researchers have been aware of aver-
sion and discomfort caused by the viewing of certain
geometric patterns (Wilkins et al., 1984). Motivated by
sporadic media reports during the past four decades of
public artworks inducing migraines, Fernandez and
Wilkins (2008) examined the spectral characteristics of
images that induce aversion. Any visual image can be
analyzed with respect to its fundamental visual proper-
ties. For instance, chromatic and brightness (luminance)
contrasts can be computed at any point in a scene. A
major property of the visual world is luminance contrast,
which can be derived at various spatial scales. An image
can be constructed from Fourier components consisting
of luminance varying sinusoidally at different spatial fre-
quencies, phases, contrasts, and orientations. One of the
fundamental properties of a visual scene is the relation-
ship between luminance contrast and spatial frequency.
In scenes from nature, the spatial frequency and contrast
of the components are related such that contrast increases
as spatial frequency decreases. When log contrast energy
is plotted against log spatial frequency, a straight line
with a slope close to −1 is typically found (Field & Brady,
1997). The image is then scale invariant: The complexity
of the scene is independent of spatial scale. In other
words, the natural visual world has a characteristic visual
property revealed with a spectral analysis.
However, this particular property is not found in
images that are uncomfortable to look at. Fernandez and
Wilkins (2008) asked participants to rate discomfort in
response to a wide variety of images, including paintings,
photographs, and meaningless images created from ran-
dom noise. Images rated as being particularly uncomfort-
able to look at possessed Fourier spectra with an excess
of contrast energy at midrange spatial frequencies rela-
tive to that expected elsewhere in the spectrum. Thus,
uncomfortable images do not possess the characteristic
visual property in which contrast amplitude decreases
linearly with increasing spatial frequency; rather, they
tend to have relatively large contrast at midrange spatial
frequencies. The discomfort depends on amplitude rather
than phase. These findings have since been confirmed by
O’Hare and Hibbard (2011).
Given the knowledge that images associated with
aversion have a characteristic spectral composition, we
examined whether trypophobia arises partly because the
inducing images possess this unusual feature, that is, rel-
ative excess of contrast energy at midrange spatial fre-
quencies. We performed a spectral analysis on a range of
trypophobia-inducing images and compared them with
control images of holes that do not induce trypophobia.
Experiment 1: Analysis of Trypophobic
Images
A total of 76 images were obtained from the trypophobia
Web site (www.trypophobia.com), including images of a
lotus seed head and a wide range of other images of
clusters of holes. We took the first 76 images presented
without prejudice; none were of the skin-lesion type. A
Google search for “images of holes” provided a set of 76
control images of holes that were not exhibited on the
trypophobia Web site as associated with trypophobia.
Using MATLAB, we cropped the images to give the larg-
est central square image, resized them to 512 × 512 pixels
(using the nearest-neighbor algorithm), rendered them in
gray level with the rgb2gray function (0–255), and nor-
malized them so that the mean gray level was 125 (SD =
25). We applied a Hanning window that reduced the con-
trast to 0 at the periphery to remove edge effects. The
fast-Fourier-transform algorithm provided an amplitude
spectrum in two dimensions, and this matrix was sam-
pled using a set of annular masks that summed the
energy over all orientations. The internal and external
dimensions of the annuli were such as to sum the energy
in bins of equal size on a logarithmic scale of spatial fre-
quency, with each bin differing from its neighbor by a
factor of a square root of 2. The four lowest spatial-
frequency bins were removed from analysis owing to the
effects of the Hanning window.
Fig. 1. Lotus seed head. Images of lotus seed heads are often reported
as inducing trypophobia.
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Fear of Holes 3
Figure 2 shows the power spectrum of the control
images and those images obtained from the trypophobia
Web site. Overall, a power function (linear on log-log
axes) accounted for more than 97% of the variance, a
good fit to the prediction for natural images. The percent-
age variance explained by the linear fit to the average
spectra for the trypophobic images of holes (95.7%) was
significantly less than for the nontrypophobic images of
holes (97.9%), t(121) = 3.31, p < .002.
These findings are consistent with a greater energy at
midrange and high spatial frequencies in the trypophobic
images. In Figure 2, the spatial frequency has been
expressed in cycles per image (cpi). Using a Bonferroni
correction for 12 paired comparisons of a probability
value of .0043, we found the difference in power between
the two functions to be significant for spatial frequencies
in the range of 45 to 181 cpi. Most photographic images
subtend 10° to 30° of visual angle, so from the viewpoint
of the camera, the excess in contrast energy ranged from
a minimum of 45 cpi divided by 30° per image (i.e., 1.5
cycles per degree, or cpd) to a maximum of 181/10 (i.e.,
18) cpd. Objects are usually photographed so that they fit
most of the frame; consequently, small objects may be
photographed from distances less than those from which
they are typically viewed, and the reverse holds for large
objects. Fernandez and Wilkins (2008) showed that the
range of spatial frequencies for which an excess energy
can be expected in uncomfortable images is from 1 to
8 cpd—a range of a factor of 8. Given this large range, it
seems likely that, even allowing for the typical viewing
distance of small and large objects, this critical spatial-
frequency range expressed in cycles per degree is within
the range for which the two curves are maximally and
significantly divergent. In sum, Experiment 1 showed that
trypophobic images have a visual property not usually
possessed by natural images: They have relatively high
contrast at midrange spatial frequencies.
Experiment 2: Generality of the
Aversion
In our second study, we examined whether aversion to
trypophobic images extends across the general popula-
tion. Fifty images obtained from the trypophobia Web site
and 50 images of holes obtained from a Google search
were presented in random order as a PowerPoint presen-
tation to 20 undergraduate students at the University of
Essex, none of whom reported being trypophobic. The
students were asked to rate any discomfort in response to
viewing the images, using scales from −5 (maximum dis-
comfort) to 5 (maximum comfort). The mean ratings for
the trypophobic and control images were −0.42 and 0.53,
respectively, t(49) = 4.67, p < .0001. Evidently, trypopho-
bic images are uncomfortable not simply for a minority of
individuals who profess to a phobia but also for individu-
als in the general population.
Experiment 3: Analysis of Images of
Poisonous Animals
In our third study, we attempted to identify the cause of
trypophobia by assessing the spectral composition of
poisonous animals. This procedure was motivated by an
individual who reported a fear of holes and told us that
certain animals also induced aversion (e.g., the blue-
ringed octopus). The common aspect of the animals
seemed to be that they were highly poisonous. We
obtained images of animals that in a large number of
Internet sources have been listed as “the 10 most poison-
ous animals.” These animals are extremely poisonous to
humans and, consequently, are commonly considered
dangerous. The 10 species were the blue-ringed octopus,
the box jellyfish, the Brazilian wandering spider, the
deathstalker scorpion, the inland taipan snake, the king
cobra snake, the marbled cone snail, the poison dart
frog, the puffer fish, and the stonefish. Ten different
images of each species were obtained from the Internet.
As with the trypophobic images, we analyzed the first 10
uncomfortable images that a Google image search gener-
ated without prejudice; our only constraint as to selection
was that the size of the image had to exceed 300 pixels
on its smaller dimension. The images were photographs
of the individual animals on a variety of backgrounds,
most of which were natural. In most of the photographs,
the animal was close to the center of the image and, in its
1
Spatial Frequency (cycles per image)
100
1,000
10,000
100,000
Fourier Power (arbitrary units)
10 100 1,000
Fig. 2. Power spectra (Fourier power as a function of spatial fre-
quency) of trypophobic (broken line) and control (solid line) images of
holes analyzed in Experiment 1.
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4 Cole, Wilkins
longer dimension, occupied more than 50% of the image.
The images were in JPEG format, which involves lossy
compression. To control for any artifacts such compres-
sion might introduce, we compared the images with
images of otherwise similar but nonpoisonous species,
sourced and prepared identically. These images were of
various nonpoisonous octopus species, nonpoisonous
jellyfish, spiders, crabs, nonvenomous snakes, nontoxic
frogs, edible snails, and edible fish.
Figure 3 shows the log contrast energy as a function of
log spatial frequency for the images of the poisonous and
nonpoisonous animals. Overall, a power function (linear
on log-log axes) accounted for more than 99% of the
variance, which again provided a good fit to the predic-
tion for natural images. The percentage of variance
explained by the linear fit to the average log spectra for
the 10 highly poisonous animals (99.1%) was less than
for the 10 control animals (99.6%), t(9) = 2.58, p = .03.
Notwithstanding the normalization of all images in terms
of pixel mean and variance, there was 15% more contrast
energy at midrange spatial frequencies in the images of
the poisonous animals (p < .05; 16–32 cpi); the size of
this difference is masked by the logarithmic scale in
Figure 3. The excess was obtained not only in the gray-
level images but also in the images formed from the R, G,
and B pixels taken separately, suggesting that the excess
was not dependent on a particular coloration or, indeed,
a particular spectral sensitivity. In sum, these results show
that the images of highly poisonous animals possess a
spectral feature similar to that of the trypophobic images.
Experiment 4: Snakes and Spiders
Some of the more common phobias are those of snakes
and spiders, and many individuals are unable to look at
images of these animals without aversion (e.g., Ohman,
Flykt, & Esteves, 2001). This is the case even in countries
in which spiders are not venomous and present no threat.
Furthermore, a number of standard behavioral measures
have been used to assess the processing priority given to
such objects. For instance, in a typical attention task,
observers are required to detect the presence of a target
item as quickly as possible. Relatively short response
times are usually taken as a marker of cognitive biases
toward particular stimuli (e.g., Crundall, Cole, & Galpin,
2007). Both adults and young children have repeatedly
been found to detect snakes more rapidly than other
kinds of stimuli. LoBue and DeLoache (2008) measured
the time taken to detect images of snakes and frogs by
young children. They found that the snakes were more
rapidly detected and that it was the coiled body shape
rather than the snakes’ sometimes-colorful markings that
was largely responsible for the conspicuity. Such a spec-
tral power distribution is likely to be conspicuous because
it differs from the spectral energy most pervasive in
nature.
Motivated by this prior work, we analyzed images of
snakes and spiders. Twenty images of snakes and 20
images of spiders with smaller dimension of at least 300
pixels were sourced from Google—again in order of
acquisition and without prejudice—and processed as in
Experiment 1. Both spectra were curved downward, as
reflected in Figure 3. A power function accounted for an
average of 98.5% (SD = 1.1%) of the variance of the
spectra of the snake images and 98.6% (SD = 1.0%) of
the variance of the spectra of the spider images. These
figures were substantially lower than those for the
images of the control animals used in Experiment 3.
Thus, as with the poisonous animals analyzed in Experi-
ment 3, images of snakes and spiders did not show the
usual linear relationship of log contrast energy to log
spatial frequency.
General Discussion
We found that images responsible for a previously unde-
scribed but relatively common form of visual phobia pos-
sess a property characteristic of images that are generally
uncomfortable to view. Such images show comparatively
high contrast energy at midrange spatial frequencies.
This confirms the results of Fernandez and Wilkins
(2008), who found a similar property in a variety of
uncomfortable images. We also found that images of ani-
mals well known to be dangerous also possess this visual
property. We therefore suggest that trypophobia arises
because the inducing stimuli share a core spectral feature
with such organisms—a feature that does not reach con-
scious awareness. In other words, if any stimulus, such as
a configuration of holes, coincidently possesses this
spectral feature, the stimulus may induce some form of
aversion because of the survival value of such aversion.
1
Spatial Frequency (cycles per image)
100
1,000
10,000
100,000
Fourier Power (arbitrary units)
10 100 1,000
Fig. 3. Power spectra (Fourier power as a function of spatial fre-
quency) of images of poisonous (broken line) and nonpoisonous (solid
line) animals analyzed in Experiment 3.
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Fear of Holes 5
This survival account is based on the notion that
humans have been selected, via Darwinian principles, for
their ability to notice poisonous organisms. The notion
that phobias can be explained by an innate predisposi-
tion to fear potentially dangerous stimuli (e.g., Marks &
Nesse, 1994) is often contrasted with the view that the
etiology of phobia is due to a learning process. Aversion
to dangerous objects is said to have resulted in modern
humans’ possessing an innate predisposition to develop
fears of certain objects, such as snakes, spiders, heights,
and so forth. An alternative Darwinian explanation is that
the ability to effectively process dangerous stimuli
evolved before humans originated. Possessing patterns as
a warning of unpalatability (i.e., aposematism) is a well-
established method of defense (e.g., Santos, Coloma, &
Cannatella, 2003). Such patterns tend to be characterized
by their high-contrasting colors at midrange spatial fre-
quencies. Furthermore, it is widely accepted that the
visual system has been selected for its ability to orient
attention to the location of a new object in the visual field
(e.g., Abrams & Christ, 2003; Cole & Kuhn, 2009, 2010).
However, conscious recognition of an object is a slow
process taking up to 350 ms (Johnson & Olshausen,
2003). Responding to a potential threat, such as a snake,
on the basis of relatively slow conscious perception
could be costly to an organism.
An alternative, more effective detection-and-avoidance
strategy might be to respond to the presence of an object
via an early, fast-acting visual mechanism based on a sim-
ple feature that is common to most dangerous animals. In
addition to the perception of motion (e.g., Cole, Heywood,
Kentridge, Fairholm, & Cowey, 2003; Skarratt, Cole, &
Gellatly, 2009), the computation of contrasts at various
spatial scales provides just such a low-level mechanism.
Support for this idea comes from other work that has
examined threat-related stimuli with respect to low-level
features. For instance, Bannerman, Hibbard, Chalmers,
and Sahraie (2012) required observers to make a saccade
to happy, fearful, or neutral faces that had been filtered
so that they had predominantly low, high, or broad
spatial frequencies. Among a number of effects,
Bannerman et al. reported that at low spatial frequencies,
fearful faces showed the fastest saccadic responses. In
contrast, there were no differences in mean latency
between any emotions for higher spatial frequencies.
Similarly, Vuilleumier, Armony, Driver, and Dolan (2003)
showed that amygdala activity was greater for the pro-
cessing of fearful expressions of faces containing low spa-
tial frequencies as opposed to high spatial frequencies.
Given the large number of images that possess
an excess of energy at midrange spatial frequencies
(Fernandez & Wilkins, 2008), it is most unlikely that this
spectral feature is a sufficient condition for phobia, even
though it is associated with aversion. Nevertheless, it may
prove possible to offer treatment by progressive spatial
filtering of the offensive images. It is, of course, still
unknown why some people develop an aversion to holes
but others do not. This issue is common to all explana-
tions of phobia; some people who have not suffered an
animal bite become phobic to dogs, whereas others who
have suffered such a bite do not become phobic.
However, our results from Experiment 2 do suggest that
nontrypophobic individuals are sensitive to the inducing
stimuli in that they perceive trypophobic images of holes
to be more aversive to look at than nontrypophobic
images of holes. Perhaps the condition is a matter of
degree, an exaggeration of a normal tendency. Finally,
although the aversion has become known as the fear of
holes, our data reveal that one essential characteristic that
induces the aversion is a particular spectral property, a
property often associated with relatively high-contrast
material at midrange spatial frequencies and not neces-
sarily involving holes.
Author Contributions
Both authors jointly wrote the manuscript and jointly carried
out all the empirical work.
Declaration of Conflicting Interests
The authors declared that they had no conflicts of interest with
respect to their authorship or the publication of this article.
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