When people are asked to assess or compare the value of experienced or hypothetical events, one of the most intriguing observations is their apparent insensitivity to event duration. The authors propose that duration insensitivity occurs when stimuli are evaluated in isolation because they typically lack comparison information. People should be able to evaluate the duration of stimuli in isolation, however, when stimuli are familiar and evoke comparison information. The results of 3 experiments support the hypothesis. Participants were insensitive to the duration of hypothetical (Experiment 1) and real (Experiment 2) unfamiliar experiences but sensitive to the duration of familiar experiences. In Experiment 3, participants were insensitive to the duration of an unfamiliar noise when it was unlabeled but sensitive to its duration when it was given a familiar label (i.e., a telephone ring). Rather than being a unique phenomenon, duration neglect (and perhaps other forms of scope insensitivity) appears to be a particular case of insensitivity to unfamiliar attributes. (Contains 2 figures and 4 footnotes.)