Thirty-one female participants (M ± SD = 19.55 ± 0.89 years) were recruited through campus advertisements. All participants were right-handed, possessed either normal vision or vision corrected to normal, and had no record of neurological or psychiatric disorders. This study received ethical approval from the Human Participants Ethics Committee of Shanghai Normal University (2022-069). Prior to the experiment, all participants were provided with detailed information about the study, including how their data (i.e., interview transcripts, subjective reports, fNIRS data, and behavioral data) would be used and shared. All participants provided informed consent and voluntarily agreed to take part in the study. The consent explicitly included permission for the anonymous and open publication of their data, including interview transcripts. Strict measures were taken to protect their confidentiality, ensuring that all information remained secure and was used only for research purposes. We closely followed ethical guidelines and institutional review board regulations to maintain privacy and ethical standards. Upon completing the experiment, each participant received a compensation of 35 RMB.
Procedures
Upon entering the laboratory, participants were introduced to a female confederate and engaged in a two-minute warm-up to foster mutual familiarity. Then, they were asked to subsequently engage in three segments of dialogue with the confederate: the pre-test talk, fat talk, and post-test talk (Fig. 1). Each conversation was initiated by the confederate who posed questions, and participants were required to answer and elaborate in detail. Notably, throughout the conversation, the confederate consistently assumes the role of the questioner, guiding participants to explore and discuss relevant topics. Each conversation lasted for five minutes.
Experimental procedure and setup.
During the pre-test talk, the confederate’s questions focused on travel (e.g., “Which scenic spots do you prefer? How do you plan your travel itinerary? How do you map out your travel route?”) or dormitory (e.g., “What style of interior design do you find appealing? How do you organize your space? What wallpapers do you recommend?”). During the fat talk, the confederate’s inquired explore participants’ bodies, asking questions like “Which part of your body brings you the most satisfaction”, “What part of your body do you find least satisfying”, “Which specific aspect of your body would you like to alter” and so on. These questions were designed to prompt participants to provide their own negative self-evaluations on the body. The content of the post-test talk mirrored that of the pre-test talk. Specifically, each participant was tasked with discussing travel, obesity, and dormitory, with the sequence of discussing travel and dormitory being randomly balanced.
Throughout each conversation, fNIRS was used to record brain signals in the frontoparietal regions of each participant. Additionally, both video and audio recordings were made of the entire conversation. After each conversation, participants completed a series of questionnaires via a data collection platform to assess their levels of body surveillance, body dissatisfaction, and emotional experiences. Following the completion of the questionnaires, participants rested for 1 minute before beginning the next segment of conversation.
fNIRS data acquisition
The brain data were collected by using the NIRSport device, manufactured by Hanxiang Company. The data was obtained at a sample rate of 7.6 Hz. Two 4 × 4 probe boards were placed on the head of each participant, and contained 16 emitters and 16 detectors. These components collectively constituted 40 measurement channels, with a 3-cm separation between optodes (Fig. 1). The alignment of fNIRS channels with measurement points on the cerebral cortex was established through the application of the virtual registration method17. This method has been validated through a multi-subject study examining anatomic craniocerebral correlation. The possible MNI coordinates of each channel (Table 1) were obtained by using the built-in software of the NIRSport device (i.e., NIRSite). The brain regions corresponding to the channels were identified using the Automated Anatomical Labeling atlas18 and verified using data from Neurosynth, a platform for the large-scale and automated synthesis of fMRI data.
Subjective measures
After each conversation, participants were required to complete several questionnaires about body surveillance, body image, and emotional experiences. To measure participants’ body surveillance, the Objectified Body Consciousness Scale (OBCS) were used19. The eight items of OBCS were evaluated on a Likert 7-point scale (“1 = Strongly Disagree” to “7 = Strongly Agree”). Total scores, obtained by summing responses, provide insights into respondents’ attitudes regarding appearance and clothing comfort.
The Body Image State Scale (BISS) was employed to evaluate an individual’s perception of their body image20. It encompasses thoughts about appearance, body shape, weight, attractiveness, and comparisons with one’s typical state and others. With six items, the BISS utilizes a Likert 9-point scoring system, where higher scores signify a more positive body image perception by the individual.
Six items from The Positive and Negative Affect Schedule (PANAS) were used to assess emotional experiences potentially related to self-objectification21. These items included Excited, Upset, Afraid, Nervous, Hostile, and Irritable. Responses were recorded on a percentage scale, with higher scores reflecting a more intense emotional experience.
Behavioral data coding
Based on the start and end times of the three conversation segments, each video was trimmed to 5 minutes, resulting in a total of 15 minutes of data divided into three 5-minute clips. These clips were processed using motion energy analysis to obtain behavioral data. Following standard research practices, the regions of interest (ROIs) were defined as the head and upper body22. The head ROI extended from a few inches above the participant’s head to the bottom of the chin, while the body ROI included the area from the bottom of the head ROI, beneath the chin, down to the horizontal surface of the couch. Motion energy parameters were recorded in a text file for each video segment.