Erotic subset for the Nencki Affective Picture System (NAPS ERO): cross-sexual comparison study

Abstract

Research on the processing of sexual stimuli has proved that such material has high priority in human cognition. Yet, although sex differences in response to sexual stimuli were extensively discussed in the literature, sexual orientation was given relatively little consideration, and material suitable for relevant research is difficult to come by. With this in mind, we present a collection of 200 erotic images, accompanied by their self-report ratings of emotional valence and arousal by homo- and heterosexual males and females (n = 80, divided into four equal-sized subsamples). The collection complements the Nencki Affective Picture System (NAPS) and is intended to be used as stimulus material in experimental research. The erotic images are divided into five categories, depending on their content: opposite-sex couple (50), male couple (50), female couple (50), male (25) and female (25). Additional 100 control images from the NAPS depicting people in a non-erotic context were also used in the study. We showed that recipient sex and sexual orientation strongly influenced the evaluation of erotic content. Thus, comparisons of valence and arousal ratings in different subject groups will help researchers select stimuli set for the purpose of various experimental designs. To facilitate the use of the dataset, we provide an on-line tool, which allows the user to browse the images interactively and select proper stimuli on the basis of several parameters. The NAPS ERO image collection together with the data are available to the scientific community for non-commercial use at http://naps.nencki.gov.pl.

Keywords: Nencki Affective Picture System; emotion; erotic stimuli; heterosexual; homosexual; sexual orientation.

Figure 1

A sample image from each category. All images were obtained from Flickr and were published under a Creative Commons license. Credits (from left to right): Charles Roffey, CC BY-NC-SA 2.0; David Shankbone, CC BY 2.0; Georgie Pauwels, CC BY 2.0; Charles Roffey, CC BY-NC-SA 2.0; Lies Thru a Lens, CC BY 2.0. For license terms see: CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/); CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/).

Figure 2

Distribution of the mean ratings obtained for 200 erotic images from NAPS ERO and 100 control non-erotic images from NAPS in the affective space of valence and arousal. Each plot represents mean ratings obtained from a different group of participants.

Figure 3

Pairwise comparisons of image ratings averaged over all subjects in a given group and over all images in a given category. Each comparison is done separately for valence and arousal. Significant differences (p < 0.05) are marked with an asterisk. Notation: HoM, homosexual males; HoF, homosexual females; HeM, heterosexual males; HeF, heterosexual females; N, Non-erotic; OC, Opposite-sex Couple; MC, Male Couple; FC, Female Couple; M, Male; F, Female.

Figure 4

Differences in the mean ratings between the respective samples (HoM—HeM, HoM—HoF, HoM—HeF, HeM—HoF, HeM—HeF, HoF—HeF) as obtained for each of the NAPS ERO images (200 erotic, 100 non-erotic), for valence and arousal separately. Each bin represents a difference in the mean ratings of a given image. Significant differences (p < 0.05) are marked by a darkening of a bin. Bins are sorted according to the size of a difference in mean ratings. Images rated higher by one group in a given comparison are aggregated on both sides of the plot, whereas images for which no difference was obtained can be found around the middle of the plot.