The efficiency of committee voting and referenda with common-interest issues critically depends on voter motivation, i.e., on voters' willingness to cast an informed vote. If voters are motivated, voting may result in smart choices because of information aggregation but if voters remain ignorant, delegating decision making to an expert may yield better outcomes. We experimentally study a common-interest situation in which we vary voters' information cost and the competence of the expert. We find that voters are more motivated to collect information than predicted by standard theory and that voter motivation is higher when subjects demand to make choices by voting than when voting is imposed on subjects.