Participants will be directed to complete the T1 survey within the week before the first session of the multi-session study. The T1 survey will assess symptoms of fear-based psychological disorders, attentional control, autonomic arousal and threat perception. Additionally, participants will complete a flanker task.

At the first laboratory session, participants will complete the Attention Network Task (ANT), the Fear Potentiated Startle (FPS) paradigm and the Multi-Source Interference Task (MSIT). Participants will be prepared for the protocol through affixing two 5 mm Ag/AgCl pre-gelled disposable electrodes approximately 1 cm under the pupil and 1 cm below the lateral canthus to assess electromyography of the orbicularis oculi muscle contraction for the FPS paradigm, and all resistance will be kept less than 6 kΩ.

Following the resting phase, the FPS paradigm will begin. For the proposed study, the aversive unconditioned stimulus (US) will be a 250-ms airblast with an intensity of 140 p.s.i. directed to the larynx. The conditioned stimuli (CS) consist of different colored shapes presented on a computer monitor utilizing SuperLab 4.0 for Windows (Cedrus, Inc.). The startle probe will be comprised of a 108 A-weighted decibel 40-ms burst of broadband noise with near instantaneous rise, which is presented via headphones after 6 s and will be followed by the US 0.5 s later. The CS+ will be paired with the airblast, while the CS- will not. Fear-potentiation and extinction occur across two active phases. The first 20 minute phase includes fear acquisition. During this period, a colored shape will be the reinforced conditioned stimulus (CS+) through its association with the aversive US. A second shape, the non-reinforced conditioned stimulus (CS-), and noise probe alone (NA) will also be presented. The conditioning phase includes three blocks of four trials of each type of stimulus (i.e., NA, CS+, CS-) in each block. All trials in both phases are presented on a fixed schedule with inter-trial intervals ranging between 18 and 25 seconds. Upon conclusion of the acquisition phase, participants complete the MSIT before beginning the extinction phase.

Following the completion of the MSIT, a 25-minute extinction phase begins. The extinction phase will consist of five blocks of four trials of each type (NA, CS+ \[unreinforced\], and CS-) in each block. Throughout the FPS paradigm, participants are asked to use a keypad to press a button marked "+" if they expect a CS to be followed by the US, a button marked "-" if they do not expect a CS to be followed by the US, and a button marked "0" if they are uncertain of what to expect. Following the FPS paradigm at T2, participants will download and learn to use the study application, whereas at T4, participants will complete the computerized post-intervention survey (same as baseline survey).

Over the course of the next 6 days following T2, participants will complete 6 sessions of the ATT or the sham control condition when prompted by the Expiwell app on their smartphone. Upon completion of the intervention, participants will complete a short assessment of their self-reported attentional control and experience of fear since the last signal. Exactly one week from the first laboratory session (i.e., same day of the week, same time of day) participants will return to the laboratory for the second lab session (T4). Participants will complete informed consent, followed by ANT, FPS, and MSIT paradigms. Upon completion of the FPS paradigm, participants will complete a computerized survey that includes measures of fear-related symptomatology and attentional control that will be modified to assess experiences over the past week. One month following the final lab session (T4), participants will be emailed the follow-up survey (T5) The T5 survey assesses fear-related symptomatology over the past month since T4.