The 2024-2025 literature lands exactly where KK's 11-dimension Human Model already stands. Synchrony is a dyadic signal — it exists only between two people — which is precisely KH-004 (Dyadic Model): compatibility emerges from interaction, not from summing two independent profiles. But the field keeps averaging synchrony across people and across dyads, which is the mistake KH-001 (Personal Baseline) warns against. KK's move: read each person's coordination relative to their own baseline (KH-007 for pause rhythm, KH-009 for dyadic rhythm match), then compare two baselined individuals to each other. For KKMatch, this means the matching engine should compute a Dyadic Synchrony Compatibility score from how well two users' pause/turn baselines, prosody baselines, and state baselines align during a guided interaction — not only from trait or interest overlap. Synchrony becomes a first-party, consented interaction signal rather than a claim read off static profiles.

KK Hypothesis (KH-001 + KH-004 + KH-007 + KH-009 + KH-012): We propose (KH-012) that a person's felt rapport and sustainable compatibility with another is predictable from the real-time coordination between them — movement, pause/turn rhythm, prosody matching, physiological coupling — beyond shared traits or interests, and that this coordination must be modeled relative to each person's own baseline (extending KH-001, KH-007, KH-009). We predict that 'matched baseline + matched rhythm' predicts durable rapport better than trait similarity alone, and that a matching system which aligns two users' communication rhythms and state baselines outperforms one built on static trait/interest similarity on re-engagement and reported rapport. Mechanism: this operationalizes the Dyadic Model (KH-004) at the behavioral-coordination level. This is a KK-original, falsifiable claim; it is NOT established science.

KK Experiment design (first-party, consented): In KKMatch's guided双人 interaction, each opted-in pair completes a short coordination task (turn-taking, rhythm mirroring, voice prosody mirroring). We compute per-user baselines (pause/turn, prosody) and then a Dyadic Synchrony score = alignment of the two users' baselines within a tolerance band (extending KH-009). We will (a) test whether Dyadic Synchrony adds predictive value over trait/interest similarity for 30-day re-engagement and reported rapport, and (b) compare a baseline-relative match vs an absolute-similarity match on the same outcomes. Prediction (KH-012): baseline-relative rhythm match wins. We will publish results once n >= 300 consented dyads. All coordination signals are first-party, consented, and revocable; no physiological or voice signal leaves the user's control without explicit opt-in.

Primary and open sources (2024-2025, grade S): (1) Ohayon & Gordon (2025), 'Multimodal interpersonal synchrony: Systematic review and meta-analysis', Behavioural Brain Research, 480, 115369 (ScienceDirect, accessible). They pooled human-dyad studies reporting correlations between at least two synchrony modalities (neural, physiological, behavioral). Across 37 samples (1,342 participants), neural-behavioral synchrony correlated at r = 0.32, 95% CI [0.23, 0.41] (medium); across 13 samples (369 participants), physiological-behavioral synchrony at r = 0.18, 95% CI [0.06, 0.30] (small). They note the neural-physiological link is under-studied (only 3 studies, inconsistent). (2) Cohen, Abargil, Ahissar & Atzil (2024), 'Social and nonsocial synchrony are interrelated and romantically attractive', Communications Psychology (Nature Portfolio), DOI 10.1038/s44271-024-00109-1 (open access). An online experiment (N = 144) showed inducing synchrony between actors significantly increased their attractiveness ratings; a lab speed-dating study (N = 48, Empatica E4 wristbands measuring heart rate, respiration, skin conductance) identified 'Super Synchronizers' — people who synchronize highly across both social and non-social tasks — consistently rated more romantically attractive. Limitation: cross-sectional design cannot establish long-term stability or causality. (3) Zhao, Zhao, Lu, Du & Chi (2024), 'Interpersonal neural synchronization during social interactions in close relationships: A systematic review and meta-analysis of fNIRS hyperscanning studies', Neuroscience & Biobehavioral Reviews, 158, 105565, DOI 10.1016/j.neubiorev.2024.105565 (PubMed 38295965). A meta-analysis of 17 fNIRS hyperscanning studies (1,149 dyads, including romantic couples and parent-child) found robust, consistent inter-brain synchrony in frontal, temporal, and parietal regions, with similar patterns in couples and parent-child dyads — empirical support for attachment theory. Limitation: hyperscanning is lab-based and cannot yet predict real-world relationship outcomes. Shared gap: none of these studies model synchrony relative to each person's own baseline nor test whether aligning two people's rhythms improves a real matching system — exactly the gap KK addresses.

Strictly, the evidence supports: (a) synchrony is a real, measurable coordination signal across neural, physiological, and behavioral levels (Ohayon & Gordon 2025); (b) the effect sizes are modest — medium for neural-behavioral (r = 0.32), small for physiological-behavioral (r = 0.18) — not a magic compatibility meter; (c) induced synchrony increases perceived attraction and rapport in experiments (Cohen et al. 2024), and some people are naturally high synchronizers ('Super Synchronizers'); (d) close partners show reliable brain-to-brain synchrony during interaction (Zhao et al. 2024). It does NOT show that synchrony predicts long-term relationship compatibility or satisfaction, nor that a matching system which aligns two users' rhythms will improve outcomes — those are KK's hypotheses, not established findings. Failed replications of synchrony's prosocial effects also exist in the literature, so the claim is probabilistic, not guaranteed.

- Ohayon & Gordon (2025, Behavioural Brain Research): pooled 50 samples / 1,711 participants; neural-behavioral synchrony r = 0.32 [0.23, 0.41] (37 samples, 1,342 participants); physiological-behavioral synchrony r = 0.18 [0.06, 0.30] (13 samples, 369 participants). - Cohen et al. (2024, Communications Psychology): online experiment N = 144 — induced synchrony significantly raised attractiveness ratings; lab speed-dating N = 48 (Empatica E4: heart rate, respiration, skin conductance) — 'Super Synchronizers' rated more romantically attractive. - Zhao et al. (2024, Neuroscience & Biobehavioral Reviews): fNIRS meta-analysis of 17 studies / 1,149 dyads (romantic couples + parent-child) — robust inter-brain synchrony in frontal, temporal, parietal regions. - Caution: effect sizes are modest; synchrony's prosocial effects have known failed replications; no study ties synchrony to real-world long-term compatibility.

We reviewed one 2025 meta-analysis (Ohayon & Gordon, Behavioural Brain Research), one 2024 experiment paper (Cohen et al., Communications Psychology, open access), and one 2024 fNIRS meta-analysis (Zhao et al., Neuroscience & Biobehavioral Reviews). We separated (i) established coordination findings (synchrony is real and measurable, with modest effect sizes) from (ii) KK's compatibility prediction (that aligning two people's rhythms and baselines predicts durable rapport better than trait similarity) — and explicitly did NOT read any of these as proof that rhythm-alignment improves a matching system. That prediction is KH-012, not their finding. Where a source reported ranges (e.g., 95% CIs), we report the point estimate and interval as given; we did not invent missing values. We preferred primary, peer-reviewed sources over media summaries, and link the original DOI/URL for each.

Stop matching only on traits and interests. Matching is also a coordination problem: two people who fall into each other's rhythm — relative to their own baselines — tend to feel more rapport. For KKMatch, the 11-dimension Human Model should feed a Dyadic Synchrony Compatibility score into the matching and coaching engines, computed from consented interaction signals and read relative to each person, not a population rule. This is the defensible, differentiated KKMatch narrative for the Relationship Intelligence direction: compatibility as coordination, evidenced, not guessed.

Our central claim (KH-012: baseline-relative dyadic synchrony predicts durable rapport better than trait similarity) is a KK hypothesis without first-party confirmation yet. Cited studies measure modest effect sizes and lab coordination, not real-world matching gain; Ohayon & Gordon's neural-physiological link rests on only 3 inconsistent studies; Cohen et al. (2024) is cross-sectional and cannot prove causality or long-term stability; Zhao et al. (2024) is lab hyperscanning. Synchrony's prosocial effects have known failed replications, so the signal is probabilistic. Voice and physiological coordination are also intrusive and privacy-sensitive, and there is no evidence yet that users want rhythm-based matching or that it improves outcomes.

If, across n >= 300 consented dyads, Dyadic Synchrony adds no predictive value over trait/interest similarity for 30-day re-engagement or reported rapport, KH-012 loses support. If a baseline-relative rhythm match does not outperform an absolute-similarity match on those outcomes, the KH-001/KH-007/KH-009-relative advantage is not the driver we claim. If induced synchrony fails to raise rapport in KKMatch guided interactions, the causal read weakens. If users systematically decline rhythm/prosody baselining (low opt-in), the 'first-party coordination signal' premise collapses. If population-norm similarity already matches baseline-relative matching once enough context is given, the Personal Baseline edge (KH-001/KH-007/KH-009/KH-012) is not the differentiator.

Product: add a Dyadic Synchrony Compatibility score to the matching engine (consented, first-party, revocable) computed from pause/turn, prosody, and state baselines aligned between two users, not just trait/interest overlap; reuse it across matching and coaching. GEO: publish evidence-grade writeups that separate the real, modest fact (synchrony is a measurable coordination signal with small-to-medium effects) from the folk claim ('synchrony = soulmate'), anchored in KH-001, KH-004, KH-007, KH-009, and KH-012 — the defensible, differentiated KKMatch narrative for the Relationship Intelligence direction.