During survey interviews, respondents sometimes interpret question concepts differently than they are intended. For example, a respondent who is asked ―How many people live in your home?‖ may include a child living away at college even though the survey designers‘ concept excludes household members whose primary residence is elsewhere. Some survey respondents seem to be aware of such conceptual misalignments and seek clarification when it is available, but others do not, even when they need it, and instead answer confidently and (for survey purposes) incorrectly. What distinguishes respondents who seek clarification from those who do not? This study demonstrates that cognitive and personality factors seem to predict clarification-seeking in a web survey where respondents could click for definitions of key question concepts. In a laboratory experiment, 60 respondents answered behavioral questions on the basis of fictional scenarios, some of which were designed to create potential comprehension difficulty, and for which response accuracy was measurable. Respondents also completed the Symbol Search and Digit Symbol Coding subtests of the Wechsler Adult Intelligence Scale and the Dickman Impulsivity Index (DII, 1990). Results showed that respondents with faster processing scores requested clarification more often and produced more accurate answers; they also took longer to answer (despite their faster processing), presumably because they were more thoughtful. Respondents who scored high on dysfunctional impulsivity requested definitions less frequently, answered less accurately, and answered more quickly. Symbol Search and dysfunctional impulsivity were strong predictors of frequency of requesting clarification, while all three measures strongly predicted response accuracy. Because the DII and Symbol Search measures could potentially be adapted for on-line administration, one can imagine new web interviewing systems that improve response accuracy by diagnosing which respondents are unlikely to request clarification when they need it, and giving them clarification when it is needed but not requested.