Adults who have attention deficit hyperactivity disorder (ADHD) suffer from significant occupational, academic and social problems, many of which are believed to be a result of problems with executive functioning. Executive functioning refers to a group of neuro-psychological functions which include sustained attention, working memory, verbal fluency, as well as motor and mental processing speed. Individuals with ADHD have been shown to have deficits in executive functioning independent of IQ, co-occurring psychiatric disorders, gender, and ADHD subtype. "Recollect" is an application (App) based working memory training video game where participants conduct 3-different adaptive working memory tasks. In each of these tasks participants are presented with a set of stimuli to be remembered while playing a simple platform game where they help navigate an astronaut across the screen and dodge obstacles. Recollect has been designed for all age groups to an interesting, fun and effective brain-training activity. The memory tasks included in the game have been independently shown to improve working memory in a manner that transfers to untrained tasks.

The purpose of this study is to evaluate the effects of playing Recollect versus Tetris for 20 minutes per day, 5 days per week over a 4 week period, on executive functioning deficits in individuals who have Adult ADHD.

The primary objective is to evaluate the effects of playing Recollect versus Tetris for 20 minutes per day, 5 days per week over a 4 week period, on executive functioning deficits in individuals who have Adult Attention Deficit Hyperactivity Disorder (ADHD).Consenting participants will be screened using the Mini International Neuropsychiatric Interview for DSM-5 (MINI) to confirm ADHD diagnosis. Participants will be asked to download either Recollect or Tetris on their own mobile device. Following a training/orientation session, they will be asked to spend 20 minutes per day at least 5 days per week playing Recollect or Tetris over a 4 week period. At Week 4, study staff will check the time log on the Recollect/Tetris App to confirm how much time was spent playing the game. Participants will be asked to complete two ADHD symptom severity scales, as well as App-based neurocognitive testing at baseline (Week 0) and endpoint (Week 4).

Inclusion Criteria:

1. Males and females aged 18 and older who own a mobile device such as a Smartphone or tablet.
2. Current diagnosis of Adult ADHD, at any stage of treatment.
3. Comorbid psychiatric conditions will be allowed.
4. Medication or psychotherapy must have been stable (no dose changes) for 4 weeks prior to study participation.
5. Must be able to read, write and understand English.

Exclusion Criteria:

1. Participant does not own a Smartphone or tablet.
2. No dose changes during the 4 week study period.
3. No initiation of new psychological therapy or counselling during the 4 week study period.