“The Point of Nipple Erection 1: The Experience and Projection of Perceived Emotional States While Viewing Women With and without Erect Nipples”, 2021 (; backlinks; similar):
[part 2]Given the research that suggests men attend to nipples and that nipple erection is triggered by sexual excitement (among other triggers), we questioned whether men see nipple erection as a sign of sexual interest. Our findings indicate that men (but not women) see women as sexier when they have nipple erection and also see themselves as sexier, supporting the idea that nipple erection is perceived signaling arousal or sexual interest.
To determine whether female nipple erection is perceived as a sign of sexual arousal or interest, male and female participants were asked to rate photos of real women with and without salient nipple erection on a series of 16 emotional and physiological states, including positive, negative, and sexually aroused states. Nipple erection salience was rated by independent raters, and faces in photos were obscured to prevent discerning emotional states from facial cues.
Men clearly projected more sexy and positive emotions onto the stimuli when the stimuli displayed erect nipples. Whereas women did project more positive emotions with erect nipples, they did not differ in their expression of sexy. We also observed that men’s self-ratings of sexy and positive emotions were the same as their ratings of the stimuli. Women, however, reported statistically-significantly less sexy and positive emotions for themselves relative to the stimuli.