Pupillometry reveals the physiological underpinnings of the aversion to holes

Abstract

An unusual, but common, aversion to images with clusters of holes is known as trypophobia. Recent research suggests that trypophobic reactions are caused by visual spectral properties also present in aversive images of evolutionary threatening animals (e.g., snakes and spiders). However, despite similar spectral properties, it remains unknown whether there is a shared emotional response to holes and threatening animals. Whereas snakes and spiders are known to elicit a fear reaction, associated with the sympathetic nervous system, anecdotal reports from self-described trypophobes suggest reactions more consistent with disgust, which is associated with activation of the parasympathetic nervous system. Here we used pupillometry in a novel attempt to uncover the distinct emotional response associated with a trypophobic response to holes. Across two experiments, images of holes elicited greater constriction compared to images of threatening animals and neutral images. Moreover, this effect held when controlling for level of arousal and accounting for the pupil grating response. This pattern of pupillary response is consistent with involvement of the parasympathetic nervous system and suggests a disgust, not a fear, response to images of holes. Although general aversion may be rooted in shared visual-spectral properties, we propose that the specific emotion is determined by cognitive appraisal of the distinct image content.

Keywords: Disgust; Fear; Holes; Psychophysiology; Pupillometry; Trypophobia; Vision.

Figure 1. Example stimuli from each stimulus category used in Experiments 1 and 2.

(A) Images from the holes category known to elicit an aversive response in trypophobes and the general population. (B) Images from the threat category generally associated with a fear response in individuals with snake and spider phobias (arachnophobia and ophidiophobia, respectively) as well as the general population. (C) Images from the neutral category used as controls in Experiment 1. (D) Images from the control category (i.e., controls for the pupil grating response) included in Experiment 2.

Figure 2. Pupillary waveforms across time for each stimulus type in Experiment 1.

The x-axis reflects trial time in seconds (s) and the y-axis reflects the percentage of pupil-size change from baseline, such that greater percent change corresponds to a smaller pupil size. Shaded colors represent standard error of the mean (SEM).

Figure 3. Pupillary waveforms across time for each stimulus type in Experiment 2.

The x-axis reflects trial time in seconds (s) and the y-axis reflects the percentage of pupil-size change from baseline, such that greater percent change corresponds to a smaller pupil size. Shaded colors represent SEM.