## 1 Introduction  
In vivo exposure therapy (iVET) is widely regarded as the most effective treatment for specific phobia (SP) [1], one of the most prevalent anxiety disorders globally [2]. Despite this, iVET faces several barriers to implementation in clinical practice, including low acceptance, high dropout rates, poor accessibility, and administering challenges in implementing it in a clinical setting [3].  
The use of mixed realities, such as Virtual Reality (VR) and augmented reality (AR), improves the limitations mentioned, particularly in terms of access and acceptability.  
Regarding increased acceptability, randomized clinical trial results showed that AR exposure was an effective and accepted treatment for SP [4].  
The previous results should motivate further investigation with mixed realities so that SP can replicate the findings in other contexts and with innovations that increase the acceptability. The present study taps into the latter goal.  
The developed projection-based AR exposure therapy (P-ARET) system [5] for small animal phobia [6] treatment enables patients to confront the feared animal (cockrach) in the real environment, projected onto a table within the treatment room. This design eliminates the need for helmets or glasses. Participants can interact with the stimulus using his or her bodies or tools, like a glass, fostering a natural interaction. Additionally, the system includes interactive activities (e.g., capturing, chasing, and killing) and environmental games. The phobic stimulus is customizable in terms of size, color, movement, and quantity, allowing the clinician to control its actions (such as dying or flapping) via a laptop. Also, it allows the phobic stimulus to be manipulated and modified in a controlled manner. This concept of stimulus \"variability\" is an important contributor to the effectiveness of the exposure technique [7; 8].  
The variability of context and stimuli seems crucial for generalizing learning. These enable individuals with SP to apply the skills learned to novel or diverse situations and stimuli that were not part of the traditional exposure therapy process [7; 9].  
Moreover, a growing body of scientific evidence has used this ecological momentary assessment (EMA) to collect experience in real-life contexts to assess anxiety disorders [10]. This approach may be particularly beneficial for individuals with SPs [11] to be able to assess their symptoms in a real context. In the present work, they face these fears, especially in the daily assessment of their fear of cockroaches. During these momentary assessments, participants are not directly exposed to cockroaches but are instead asked questions throughout the day based on hypothetical encounters with cockroaches. However, it is possible that during this period, participants may encounter real-life situations where they come across cockroaches, such as on the street, at home, or in the workplace, or engage in activities that typically trigger their anxiety, like walking outside at night or taking out the trash. These real-world experiences allow participants to respond more authentically to questions than they would in a controlled laboratory setting, thus providing a more accurate measure of their phobia progression and responses to stimuli.  
This study aimed to explore the feasibility of using P-ARET to present a variety of phobic stimuli to participants diagnosed with cockroach phobia. A key study goal was to compare participants' experience with multiple stimuli (MS) versus single stimulus (SS) conditions. As a secondary objective, we analyzed the adherence to a daily monitoring app (_Emotional Monitor_). A final secondary goal was to assess the preliminary efficacy of the P-ARET treatment.