The training app for the control condition was based on an open source code for a popular cognitive training app called 2048 that is marketed as a fun and relaxing puzzle game. Within 2048, participants slide numbered tiles around a grid, matching tiles of the same value. Instead of tiles disappearing, as in Candy Crush or other similar grid-sliding games, matching 2 numbered tiles in 2048 combines them into 1 new tile displaying the sum of the previous 2 numbers. For example, two 2-tiles linked side-by-side become a 4-tile, whereas 2 matched 4-tiles become an 8-tile, and so on. The goal is to match tiles until the sum of 2048 is reached on a single tile. There is no time limit.

A 20-item self-report scale that measures 2 components of mindfulness: awareness and acceptance. Respondents rate a series of statements on a 5-point likert scale, with 1 being never and 5 being very often. This scale yields two scores, one for each subscale: awareness and acceptance. On the awareness scale the minimum possible score is 10 and the maximum is 50. Higher values on this subscale represent higher levels of awareness (better outcome). For the acceptance subscale, the minimum possible score is 10 and the maximum is 50, with higher values representing higher levels of acceptance (better outcome).

A 32-item self-report scale that measures the multidimensional construct of interoceptive body awareness. Respondents rate a list of statements on a 6-point likert scale, with 0 being never and 5 being always. This measure yields 8 scores, one for each of the subscales: noticing (min-max range: 0-20), not distracting (min-max range: 0-15), not worrying (min-max range: 0-15), attention regulation (min-max range: 0-35), emotional awareness (min-max range: 0-25), self-regulation (min-max range: 0-20), body listening (min-max range: 0-15), and trusting (min-max range: 0-15). On each of these subscales, higher values represent higher levels of interoceptive body awareness (better outcome).

A 23-item self-report scale that measures a person's faith and spiritual journey. Respondents rate a list of statements on a 6-point likert scale, with 1 being strongly disagree and 6 being strongly agree. This measure yields two scores, one for each subscale: spiritual support (min-max range: 13-78) and spiritual openness (min-max range: 10-60). On the spiritual support subscale, higher values represent higher levels of spiritual support (better outcome). On the spiritual openness subscale, higher values represent higher levels of spiritual openness (better outcome).

A 10-item self-report scale that measures 2 dimensions of the meaning in life and as such includes 2 subscales: presence of meaning and search for meaning. Respondents rate statements on a 7-point Likert scale, with 1 being absolutely untrue and 7 being absolutely true. On the presence of meaning subscale the minimum possible score is 5 and the maximum is 35, with higher values representing the degree that participants feel they have meaning in their lives (better outcome). On the search for meaning subscale the minimum possible score is 5 and the maximum is 35, with higher values representing the extent that individuals are searching for meaning in their lives (better outcome).

The mood board is a visual representation of negative and positive emotions on a spectrum, ranging from intense emotions to mild emotions. This mood board provides a maximum of 32 emotions that a participant can select by clicking on that emotion. This measure yields 4 scores one for each subscale. Each subscale has a minimum possible score of 0 and maximum of 8. Higher values on the intense negative emotions subscale represent greater levels of intense negative emotions (worse outcome). Higher values on the intense positive emotions subscale represents greater levels of intense positive emotions (better outcome). Higher values on the mild negative emotions subscale represents greater levels of mild negative emotions (worse outcome). Lastly, higher values on the mild positive emotions subscale represents greater levels of mild positive emotions (better outcome).

This is a 10-min version of the Attention Network Test that measures 3 different functions of attention:

alerting, orienting, and conflict monitoring.

This is a newly developed behavioral task created in our laboratory to assess interoceptive attention.

Mood was measured via self-report on the smartphone app. This measurement was taken before and after each use of the smartphone app in their assigned condition.

Stress was measured using a visual analogue scale on a smartphone app where participants would rate their level of stress by sliding a bar along the scale. They would slide the bar to the green side of the scale if experiencing low levels of stress and to the red side of the scale if experiencing high levels of stress. This is a continuous scale with a minimum possible score of 0 and a maximum score of 1, with higher values representing greater levels of stress (worse outcome). This measurement was taken before and after each use of the smartphone app in their assigned condition.

Heart rate was measured using the camera on the smartphone app using a well established algorithm. This measurement was taken before and after each use of the smartphone app in their assigned condition.