Abstract
Eckhart Hess (1965) claimed that pupils dilate to pleasing images and constrict to displeasing images. This work has been most severely criticized on two grounds; first, the luminances and contrast of the images across conditions were not kept constant, and second, the pupil only constricts to light (Loewenfeld, 1966). To correct for these confounds we presented rightward or leftward facing male and female portraits by Rembrandt for 20 seconds each on a CRT in either their original (n=20) or mirror-reversed position to 30 observers while measuring their pupil size. After presenting each portrait, observers used a 1–9 Likert-scale to report how (dis)pleasing they found each image. We then took their difference in “pleasingness” ratings between the original and mirror-reversed images, and correlated it with the difference in average pupil diameter obtained between the original and mirror-reversed images. We found that differences in “pleasingness” ratings did not alter observer's difference in pupil size while viewing the female images. However, we found a strong correlation between differences in “pleasingness” ratings and observer's pupil size while viewing male portraits. Surprisingly, we found that as observers rated one of the image pairs (original viewing versus mirror-reversed) more displeasing their pupil size increased. This contradicts Hess' original findings (which predict a decrease in pupil size with more displeasing images). However, it agrees with Libby, Lacey & Lacey (1973) and suggests that perceived threat (connoted as “displeasing”) correlates with an increase in pupil diameter as Darwin (1890) would have predicted.
References:
Darwin (1890). The Expression of the Emotions in Man and Animals, D. Appleton & Co., N.Y.).
Hess (1965). Attitude and pupil size. Scientific American, 212, 46-54.
Libby, Lacey & Lacey (1973). Pupillary and cardiac activity during visual attention. Psychophysiology, 10(3), 270-294.
Loewenfeld (1966). Comment on Hess' findings. Survey of Ophthalmology, 11, 291-294.