Which ONE feature could help to differenciate Alzheimer's Dementia from Delirium in a 70 year old man with Urinary Tract Infection?

Delirium is broadly defined as an acute decline in attention and cognition. It is characterized by altered sensorium, confusion, stupor, and fluctuations of consciousness. Dementia is defined as a progressive impairment of cognitive functions occurring in clear consciousness (i.e. in the absence of delirium).