In other studies, stimulus duration is controlled, not by the experimenter, but by the participants themselves. That is, participants experienced the stimulus as long as they wished before giving their response, either in a lab (e.g., Augustin & Leder,
2006; Locher, Krupinski, & Schaefer,
2015; Millis,
2001) or while being observed in an art gallery (Kontson et al.,
2015; Pelowski,
2015). In those studies, stimulus duration was neither controlled nor a variable of interest. In other studies, self-determined stimulus duration (viewing time) is the dependent variable. Viewing time has been used to measure preference in infants (Bayet et al.,
2015; Langlois, Ritter, Roggman, & Vaughn,
1991; Liu et al.,
2015; Ramsey, Langlois, Hoss, Rubenstein, & Griffin,
2004; Slater et al.,
1998) and predicts adult preference for abstract colored shapes (Holmes & Zanker,
2012,
2013). Viewing time has also been used to measure the extent to which a stimulus is desired (“wanting”) in key-press tasks that allow the participant to prolong viewing by repeatedly pressing a key (Aharon et al.,
2001; Dai, Brendl, & Ariely,
2010; Parsons, Young, Kumari, Stein, & Kringelbach,
2011; Sprengelmeyer, Lewis, Hahn, & Perrett,
2013; Wang et al.,
2015). The number of key presses then indicates how much participants “want” the stimulus—that is, how much effort they are willing to exert prolonging the experience. To an economist, finding that people will work to prolong pleasant stimuli implies that value increases with duration. This accords with Bentham's (
1789/2007) suggestion that value is fundamentally the product of pleasure and duration.