Simple Cognitive Task After Trauma

Inclusion Criteria: * Aged 18 or over * Experienced or witnessed a traumatic event resulting in admission to the emergency department for example a road traffic accident (as a driver, passenger, motorcyclist, cyclist or pedestrian) * Met the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM5) criterion A for Post-Traumatic Stress Disorder (PTSD) ("The person was exposed to: death, threatened death, actual or threatened serious injury, or actual or threatened sexual violence" by "Direct exposure" or "Witnessing the trauma") ) * Can be seen in the emergency department within 6 hours after the traumatic event * Report memory of the accident * Fluent in Swedish * Alert and orientated * Have sufficient physical mobility use the intervention platform (their smartphone) to play a computer game or engage in other smartphone activities at the point of taking informed consent (i.e. sufficient use of hands). * Willing and able to provide informed consent and complete study procedures * Willing and able to be contacted following discharge to complete follow-up assessments * Have access to an internet enabled smartphone * in addition to point above "can be seen in the emergency department within 6 hours after the traumatic event", from mid May 2019, to also include patients presenting later to the emergency department if still within 72 hours of the event Exclusion Criteria: * Loss of consciousness of \> 5 minutes * Current intoxication * Report a history of sever…