[The effects of response cost and time on choosing a stimulus].

We investigated how people develop preferences for stimuli, as a function of different levels of response cost. In Experiment 1, participants learned to discriminate between stimuli that followed high-cost versus low-cost responses. Contrary to previous studies of pigeons, participants chose the stimulus that appeared after a single response. In Experiment 2, three kinds of discriminations (low-cost, high-cost, and delay conditions) followed a single response, 20 responses or a five-s delay period, in order to examine how temporal factors affect choice. Participants with fast reaction times chose the stimuli in the low-cost condition, over those in the high-cost and delay conditions. Participants with slow reaction times chose the stimuli in the high-cost condition over those in the low-cost condition. These results suggest that temporal factors may become critical when choosing a stimulus that is presented after the response. These results are discussed in terms of the difference between expected and actual values of the reward, which determined stimulus preference either by virtue of contrast or assimilation.