Effects of effort and difficulty on human preference for a stimulus: Investigation of the within-trial contrast.

The within-trial contrast hypothesis (WTC) provides a more parsimonious explanation for the phenomenon that humans and animals prefer outcomes that follow more effortful events to outcomes that follow less effortful events (Zentall, 2013). We conducted two WTC experiments with human adults. In Experiment 1, we manipulated the difficulty of a preceding event by varying the interresponse time and the limited-hold interval during differential reinforcement with a low response rate schedule, to examine the effect of effort on the preference for the subsequent stimuli.