In the introduction to her project Experimental Relationship, the New York-based photographer Pixy Liao writes: “As a woman brought up in China, I used to think I could only love someone who is older and more mature than me, who can be my protector and mentor. Then I met my current boyfriend, Moro. Since he is five years younger than me, I felt that the whole concept of relationships changed, all the way around. I became a person who has more authority and power. One of my male friends even questioned how I could choose a boyfriend the way a man would choose a girlfriend. And I thought: ‘Damn right. That’s exactly what I’m doing, and why not!’” Experimental Relationship is a deadpan examination of that perceived reversal of power. Liao creates situations in which Moro appears passive or submissive to her whims in order to “explore the alternative possibilities of heterosexual relationships”. The series has fun with the expectations of the male gaze. Sometimes, Liao is clothed in the portraits and Moro is naked. She carries him over her shoulder in a fireman’s lift, or eats her breakfast off his unclothed body, or stares uncompromisingly into the camera while he places his head, childlike, on her shoulder, or tweaks his nipple. The pictures are more comical than coercive. Here, Moro seems to be getting the wrong end of the candy floss, while Liao enjoys his slight discomfort. The picture is included in a new guide to portrait photography, The Portrait Photographer’s Manual, in the “Family and Friends” section. Liao met Moro on their first day at art school in Memphis. She began taking the pictures after they had been dating for a year; she got the idea from the reaction of Chinese friends and family to her having a younger boyfriend. She and Moro now live together. The project is continuing. The Portrait Photographer’s Manual is published on 20 July by Thames & Hudson (£16.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply