Abstract
The pupil has been shown to be sensitive to the emotional content of stimuli. We examined this phenomenon by comparing fearful and neutral images carefully matched in the domains of luminance, image contrast, image color, and complexity of content. The pupil was more dilated after viewing affective pictures, and this effect was (a) shown to be independent of the presentation time of the images (from 100–3,000 ms), (b) not diminished by repeated presentations of the images, and (c) not affected by actively naming the emotion of the stimuli in comparison to passive viewing. Our results show that the emotional modulation of the pupil is present over a range of variables that typically vary from study to study (image duration, number of trials, free viewing vs. task), and encourages the use of pupillometry as a measure of emotional processing in populations where alternative techniques may not be appropriate.
Highlights
The pupil has been shown to be sensitive to the emotional content of stimuli
Average baseline-corrected data were entered into a 2 3 4 analysis of variance (ANOVA) with factors of emotional content and duration (100, 300, 1,000, 3,000 ms)
In order to perform a 10 3 2 3 4 ANOVA with factors of trial position within-block (1–10), emotional content, and block (1–4), missing values were imputed with the mean value calculated using a Markov chain Monte Carlo multiple imputation method
Summary
The pupil has been shown to be sensitive to the emotional content of stimuli. We examined this phenomenon by comparing fearful and neutral images carefully matched in the domains of luminance, image contrast, image color, and complexity of content. When a person becomes aroused or excited, the pupil enlarges (Snowden, Thompson, & Troscianko, 2012) Given this response, it is not surprising that researchers have used pupillometry as a physiological measure of psychological processes (Laeng, Sirois, & Gredeback, 2012). The pupil controls the amount of luminance reaching the retina, but light level and the state of retinal adaptation are not the sole influence on the actual size of the pupil Work in this area (Hess & Polt, 1960) showed that the pupil appears to react to the specific meaning of the pictures rather than the mere presentation of patterns of light and dark.
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