An 80-year-old man undergoes an evaluation for dementia versus depression. His caregiver describes a history of a gradually worsening depressed mood and confusion，with poor appetite，weight loss，poor self-care，and irritability，On his cognitive examination，he is alert and oriented to person and place but not to time. His concentration is impaired,and he displays poor short-term memory despite adequate recall.His effort is poor overall and he often responds to question stating “I don’t know”. Which of the following features is more consistent with a depressive illness than with dementia