This randomized controlled trial examines the effects of a mobile-based gamified combined cognitive bias modification (CBM-C) intervention on obsessive-compulsive symptoms, obsessive beliefs, attentional and interpretation biases, depressive symptoms, and psychological distress. The gamified CBM-C condition is compared to a standard mobile-based CBM-C and a placebo control condition. All interventions are delivered via a mobile application. Assessments are conducted at baseline, post-intervention (week 4), and 3-month follow-up.

Cognitive Bias Modification (CBM) is a cognitive intervention that experimentally modifies cognitive biases by using a series of disorder-related stimuli designed to manipulate cognitive processes relevant to psychopathology. There are two major forms of CBM interventions: Cognitive Bias Modification-Attention (CBM-A) and Cognitive Bias Modification-Interpretation (CBM-I). CBM is also a promising treatment for Obsessive- Compulsive Disorder (OCD). In recent years, there has been a growing consensus that there may be causal relations among different cognitive biases ("combined cognitive bias hypothesis"). In line with this hypothesis, it is reasonable to suggest that modification in one section will also have an impact on other biases. There are a few studies testing the effect of Combined CBM (CBM-C) programs on anxiety symptoms, depressive symptoms, and OCD symptoms in subclinical samples with promising results.

In recent years, gamification has also been used in order to increase motivation and participation in experimental tasks that constitute the content of both CBM-A and CBM-I interventions. It is possible to see examples of this method in the field of mental health in general and it is stated that it has the potential to be effective as an intervention on reducing the symptoms of psychiatric disorders. However, there is no study to investigate the effect of gamified CBM in individuals with OCD. Based on these new developments and their positive effects, the aim of the study is to investigate the effect of the gamified CBM-C on reducing the severity of OCD symptoms, obsessive beliefs, interpretation and attentional biases, depressive symptoms, and psychological distress, and increasing motivation and participation in experimental tasks.

The study will be conducted on adult participants primarily diagnosed with OCD according to the DSM-5 criteria by a psychiatrist at Dokuz Eylul University Hospital and referred for outpatient treatment at the same hospital. Participants will be randomly assigned to one of three groups: gamified CBM-C, standard CBM-C, or a placebo control condition. The intervention will be delivered via a mobile phone. Data collection will include self-report assessments and behavioral tasks. Attentional bias will be measured using a dot-probe task with eye-tracking, and interpretation bias will be assessed through a recognition scenario task. Measurements will be taken at baseline, post-intervention (week 4), and at 3-month follow-up.

It is expected that participants in the gamified CBM-C condition will demonstrate greater improvements across clinical symptoms, cognitive biases, and motivational outcomes compared to participants in the standard CBM-C and placebo control groups. To the best of current knowledge, this study will be the first to evaluate the effects of a gamified CBM-C intervention in individuals diagnosed with OCD. Its findings are anticipated to contribute to the development of scalable, accessible, and cost-effective digital interventions for clinical populations with elevated dropout and relapse rates.

Inclusion Criteria:

• Age 18 years or older
• Primary diagnosis of obsessive-compulsive disorder (OCD), confirmed by a licensed clinician using the Structured Clinical Interview for DSM-5 (SCID-5)
• No current suicidal ideation or psychotic symptoms
• Access to the internet and a mobile phone
• Stable psychiatric medication use for at least one month prior to enrollment, with no changes in dosage during the 4-week intervention period
• No current neurological or medical condition that would interfere with participation
• Ability to perceive colored visual stimuli (e.g., no color blindness)
• Not currently enrolled in another intervention-based study
• Not receiving any other form of psychological treatment at the time of participation

Exclusion Criteria:

• Presence of active suicidal ideation or psychotic symptoms
• Unstable psychiatric medication use (e.g., recent dose change within the past month or expected change during the intervention period)
• Significant neurological or medical illness that may interfere with participation
• Visual impairments that would prevent accurate perception of colored stimuli (e.g., color blindness)
• Current participation in another clinical trial involving psychological intervention
• Receiving concurrent psychotherapy or other psychological treatments outside of the study

The participants will know that they will receive a treatment, but they will be blinded to randomization, i.e. will not know which groups they can be randomized to.