Background: Mindfulness research faces two structural problems. First, weak active control conditions make it impossible to isolate specific mechanisms from expectancy and non-specific effects. Second, most protocols systematically exclude low-socioeconomic status (SES) populations through design assumptions that presuppose high literacy, quiet private spaces, and familiarity with contemplative practice.

Objective: This study validates the Standardized Open-source Mindfulness Architecture (SOMA), the first modular, open-source stimulus library purpose-built to address both challenges simultaneously. SOMA comprises 88 distinct audio assets organized around 16 sensory practice modules, each paired with a structurally equivalent active control script engineered to induce analytically orthogonal cognitive processing.

Design: Pre-registered randomized controlled trial using a 2×2 mixed design (Condition [Mindfulness vs. Active Control] × Measure [State Mindfulness Scale vs. Analytical Engagement Scale]), with quota sampling to ensure equal representation of participants with and without a university-level degree (n = 180 per SES stratum).

Setting: Online, via Prolific Academic recruitment platform and Qualtrics survey software.

Participants: N = 360 English-proficient adults aged 18 years and older (or the applicable minimum age of majority in the participant's country of residence) without a current mental health diagnosis or treatment, and without a current meditation practice.

Intervention: Each participant listens to a single 12-minute audio-guided exercise. Participants are randomly assigned to either the Mindfulness condition or the Active Control condition, and within that condition to one of 16 practice scripts. Mindfulness scripts guide bottom-up experiential awareness; Active Control scripts guide top-down analytical processing of the same everyday activities.

Primary Outcomes: (1) Credibility and expectancy equivalence between conditions (H1: Two One-Sided Tests on Credibility and Expectancy Questionnaire composite, equivalence bounds d = ±0.40); (2) mechanistic double dissociation - higher state mindfulness in the Mindfulness condition and higher analytical engagement in the Active Control condition (H2: 2×2 mixed ANOVA, interaction term as primary criterion).

Exploratory Outcome: SES-related differential experiential accessibility (H3: independent-samples t-test plus equivalence test on Semantic Differential composite by SES group).

The SOMA Validation RCT is a proof-of-concept deployment of the Standardized Open-source Mindfulness Architecture (SOMA) library, testing whether the library's two core design goals - mechanistic orthogonality between Mindfulness and Active Control conditions, and equitable accessibility across socioeconomic strata - have been achieved before the library is used in large-scale multi-site efficacy trials.

The study uses a randomized, single-blind, parallel-group 2×2 mixed design. Each participant is randomly assigned to either the Mindfulness condition or the Active Control condition and listens to a single 12-minute audio track. Within each condition, participants are further randomized to one of 16 practice scripts, with approximately equal allocation across scripts. Mindfulness and Active Control scripts are structurally matched on duration, word count, and narrator voice, and cover the same 16 everyday activities and sensory domains - the difference lies exclusively in the cognitive mechanism targeted. Blinding is achieved via a neutral cover story framing both conditions as "Mental Efficiency Training." Researchers analyzing data are not blinded.

Three pre-registered hypotheses are tested. H1 (confirmatory) tests whether the Active Control condition is perceived as equally credible as the Mindfulness condition, using Two One-Sided Tests (equivalence bounds d = ±0.40, one-sided α = .05) on the Credibility and Expectancy Questionnaire (CEQ) composite, with script assignment as covariate. H2 (confirmatory) tests whether the two conditions produce a mechanistic double dissociation - Mindfulness greater than Active Control on the State Mindfulness Scale (SMS) and Active Control greater than Mindfulness on the Analytical Engagement Scale (AES) - using a 2×2 mixed ANOVA (Condition × Measure). The interaction term is the primary confirmatory criterion (α = .05); planned one-tailed contrasts provide confirmatory directional evidence. The SMS measures bottom-up experiential awareness; the AES, developed specifically for this study, measures top-down analytical engagement. H3 (exploratory) tests whether Low-SES and High-SES participants show equivalent experiential responses on a Semantic Differential composite, using an independent-samples t-test plus equivalence test (bounds d = ±0.40).

Primary analyses follow an intention-to-treat approach: all participants who completed the study are included regardless of performance on the Script Comprehension Check. A pre-specified sensitivity analysis repeats all primary analyses excluding participants who fail both Script Comprehension Check items. In the unlikely event that the target N of 360 is not reached within four weeks of launch, data collection will close and analyses will proceed on the achieved sample, with any shortfall reported transparently as a deviation.

Quota sampling is used at the recruitment stage to ensure n = 180 per SES stratum (Low-SES: no university-level degree; High-SES: university-level degree or higher), recruited via two linked studies on the Prolific Academic platform with mutual exclusion between studies. SES is not used as a stratification variable at the randomization stage.

Full pre-registration, analysis code with simulated data, and all stimuli are available at osf.io/m76cg.

Inclusion Criteria:

Aged 18 years or older (or the legal age of majority in the participant's country of residence, whichever is higher)

Fluent in English (English as first language or self-reported fluent language)

Able to listen to a 12-minute audio recording with headphones, earphones, or device speaker

Access to a device capable of completing an online survey

Exclusion Criteria:

Current diagnosis of a mental health condition

Currently receiving or waiting for treatment for mental health symptoms (e.g., psychological therapy or psychiatric medication)

Regular yoga or meditation practice in the last six months

De-identified participant-level data will be shared in a public repository (Open Science Framework, osf.io/m76cg) after study completion and publication. The dataset will include all survey responses (excluding any inadvertently identifying information) and the analysis code needed to reproduce all reported results. Data sharing is a pre-specified condition of participation and is disclosed in the participant information sheet.

De-identified individual participant data and all supporting information will be available on the Open Science Framework (osf.io/m76cg) within 12 months of primary study completion. Data will remain publicly accessible indefinitely.

Open access. No registration or application required. All de-identified data, analysis code, study protocol, statistical analysis plan, and informed consent form will be freely available for download at osf.io/m76cg. Data are shared under CC BY-NC-SA 4.0 - free for academic, clinical, and public research use.

Participants are blinded to condition assignment via a neutral cover story ("An Investigation of Audio-Guided Mental Training for Focus and Perception"). Both conditions are presented under a "Mental Efficiency Training" rubric within the survey. Investigators and outcome assessors are not blinded.