'Wired for Empathy: Family Synchrony During Emotional Disclosure'

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1) Have any data been collected for this study already?
No, no data have been collected for this study yet.

2) What's the main question being asked or hypothesis being tested in this study?
Our study investigates whether interbrain synchrony (IBS) in the right temporoparietal junction (rTPJ) and right inferior frontal gyrus (rIFG) is higher across family members during an empathy-eliciting conversation compared to a non-empathic control conversation. We also examine whether this empathy-elicited IBS is associated with greater perceived success of emotional disclosure, higher levels of situational cognitive and affective empathy, and higher perceived closeness between family members.

Hypotheses
H1: Family members will show higher IBS during the empathy-eliciting conversation compared to the non-empathic control conversation.
H2a-c: A greater increase in IBS from the control to the empathy-eliciting conversation will be associated with a) higher perceived success of emotional disclosure, b) higher levels of cognitive and affective empathy between family members, c) greater perceived closeness between family members.

3) Describe the key dependent variable(s) specifying how they will be measured.
Interbrain Synchrony (IBS)
We will use functional near-infrared spectroscopy (fNIRS) to measure brain activation in the right temporoparietal junction (rTPJ) and the right inferior frontal gyrus (rIFG) in a hyperscanning setup, with all family members recorded simultaneously.

IBS will be quantified using Wavelet Transform Coherence (WTC) analysis. WTC will be computed for each dyad within the family, separately for the empathy and control conditions. Only task epochs (i.e., the conversation periods) will be included in the analysis. Our frequency-of-interest is 0.06Hz – 0.15Hz (based on Jiang et al., 2015, which shows that during free-flow conversation synchrony occurs around 6s to 15s). We will use a channel of interest approach.

Closeness Between Family Members
We will assess perceived interpersonal closeness using an adapted task version of the Inclusion of Other in the Self (IOS) scale (Aron et al., 1991). In this dynamic version, each family member is presented with a set of circle pairs (each pair representing a specific family member and themselves). They can drag these circles to indicate perceived closeness. Greater overlap between circles reflects higher perceived closeness across family members. Participants complete these for all possible combinations of themselves and family members (one-by-one), as well as for the family all together (with each circle/member appearing subsequently and with all circle/members remaining on the screen) We will look at closeness at the dyadic as well as at the family level.

Success of Emotional Disclosure
After each conversation, each family member will rate (on a scale from 1 to 7): How well did you feel listened to by the others? (for the family member that disclosed during the conversation)
How well do you think you listened to the others? (for the family member(s) that listened to the disclosing during the conversation)
Higher scores indicate a greater sense of successful disclosure.

Cognitive and Affective Empathy
To assess empathy, each family member will rate (on a scale from 1 to 7):
How they themselves felt during the conversation and how they think each other family member felt during the conversation.
Cognitive empathy will be calculated as the absolute difference between a participant's estimate of another family member's emotions and that person's actual self-report. Smaller distances indicate greater emotion recognition accuracy, interpreted as higher cognitive empathy.
Affective empathy will be calculated as the absolute difference between the self-reported emotions of two family members. Smaller distances reflect greater emotional alignment, interpreted as higher affective empathy.

4) How many and which conditions will participants be assigned to?
Conditions
• Empathy Condition (experimental):
The cards contain emotional and empathy-eliciting questions, designed to evoke emotional and empathic responses from other family members.
• Neutral Condition (active control):
The cards contain neutral and less emotionally charged questions, designed to mimic the structure and timing of the empathy condition without evoking an empathetic response.
Each family will participate in both the empathy-eliciting condition (experimental, adapted from Quasier et al., 2023) and the neutral condition (active control), with each condition repeated twice (randomised). Both conditions follow this structure:
1. Initial sharing phase (1 min):
One family member selects a card with a prompt and answers the question aloud. During this phase, only the selected participant is allowed to speak, while the others listen.
2. Open conversation phase (1.5 min):
The other family members can respond and react in a free-flowing conversation based on the initial sharing phase. All participants may contribute.

5) Specify exactly which analyses you will conduct to examine the main question/hypothesis.
We will conduct multilevel modeling using linear mixed-effects models (LMMs) to account for the nested structure of the data.
For each hypothesis, we will begin with a maximal random effects structure (Barr et al., 2013), including random intercepts and random slopes. We will include random intercepts for participant, dyad, and family. If the model fails to converge, we will simplify the random effects by removing the slopes/correlations.
We will conduct confirmatory analyses to test whether IBS increases during the empathy condition (H1), and whether this increase predicts perceived success of emotional disclosure (H2a), cognitive and affective empathy (H2b), and perceived closeness between family members (H2c).

6) Describe exactly how outliers will be defined and handled, and your precise rule(s) for excluding observations.
Participants with missing fNIRS data or with signal loss will be excluded from the IBS analyses per trial if less than 50% of usable data remain. fNIRS channels will be excluded one by one after visual inspection of data. Self-reported data will be excluded per timepoint if missing/incomplete.

7) How many observations will be collected or what will determine sample size?
No need to justify decision, but be precise about exactly how the number will be determined.
We will actively test families until the 28th February 2026 or until we have tested 60 families with complete data (whichever comes first). If during a testing session, the family is not complete, we will still collect and use the data as long as there are two family members (including one child and one parent) present.

8) Anything else you would like to pre-register?
(e.g., secondary analyses, variables collected for exploratory purposes, unusual analyses planned?)
For the TPJ, we will use a functional channel-of-interest approach, identifying channels based on significant activation during a separate TPJ localizer task. The localiser task consists of watching a short movie ('Partly Cloudy'). These will be cross-referenced with photogrammetry-based co-registration to MNI space to ensure anatomical correspondence.
For the IFG, we will use an anatomically defined channel-of-interest approach, selecting channels located over the IFG based on photogrammetry and standard MNI-space mapping.
Regarding the frequency of interest, as multiple studies refer to differences in frequency bands (Park et al., 2023), we will exploratively consider different frequency ranges as well. In the manuscript we will transparently communicate about these additional ranges. We will use a channel of interest approach
Additional measures: We will record the whole session on video + audio.
Explorative analysis: we will investigate whether effects differ across dyad types (e.g., sibling–sibling, parent–child, parent-parent), which may reflect differences in relationship dynamics and roles. We also plan to compare neural synchrony measures to behavioural synchrony (e.g., turn-taking, gaze), as well as conversation patterns (e.g. relevance, contingency, intrusiveness, Nguyen et al., 2020). Lastly, we are interested in looking at differences in synchrony between the two regions of interest (rTPJ and rIFG).
We will also exploratively compare across families to understand predictors of family relationship quality in relation to synchrony and other family-dynamics. One key aspect will be ownership and usage of AI: we will compare families who own AI at home (e.g., social robots, digital voice assistants), those who own pets (reference category), and those who do not own either (control group). We aim to include 20 families per category.