Inclusion Criteria:  18 and 29 years Those who use ENDS exclusively, not combining with other tobacco, for 3 consecutive months Those who own a smartphone.  Exclusion criteria:  Current medication or psychosocial treatment for ENDS dependence Serious alcohol-use problems (≥ 26 points on the Alcohol Use Disorders Identification Test) Ophthalmic conditions impeding eye-tracking Current psychiatric/psychosocial treatment for other mental health disorders in the DSM-5 (e.g., schizophrenia) Pregnancy.