A 24-year-old man is brought to the emergency department by his roommate after exhibiting paranoid delusions and auditory hallucinations for the past 3 weeks. Urine drug screen is positive for methamphetamine. The patient's roommate reports the patient has been using methamphetamine heavily for the past 2 months but that the patient had been "acting strange and talking to himself" even during a 10-day period when they were on a camping trip with no access to substances. The patient has no prior psychiatric history. Which of the following findings is most important in differentiating substance-induced psychotic disorder from a primary psychotic disorder in this patient?