Time perception/judgment is relevant to everyone and is an integral part of decision making, because any meaningful choices are embedded in a temporal context. The unpacking effect (Tversky & Koehler, 1994) in probability judgment refers to a phenomenon where “unpacking” an event could increase the subjective probability judgment of the event. Given the similarity of time and probability in intertemporal and risky decision making and based on the results of plan fallacy research, we conject that the unpacking effect may also be detected in time perception/judgment. Unlike previous research that focused on the unpacking manipulation of some events, we only used pure manipulation on a time interval. We named this phenomenon the time unpacking effect, where a time interval is presented in an unpacked rather than compact way, thus lengthening subjective time perception. In this research, two studies explored the time unpacking effect in judgment and intertemporal decision making, and the impact the effect has on intertemporal decision making.
Study 1 tested this effect in temporal judgment of whether a given time is sufficient to complete a task. Hypothesis 1a states that people in the unpacking condition compared with those in the packed condition will have higher scores, meaning they will perceive the time period as longer. Based on previous research, we formulated hypothesis 1b stating that task difficulty will affect the time unpacking effect. The experiment used a between-subjects design, where 124 participants were randomly assigned to a packed or unpacked condition and were presented with two scenarios within which tasks of varying difficulty were presented and asked to finish the corresponding computerized questionnaires. As a control factor we measured the participants’ degree of busyness during the specified time periods. A mixed design MANOVA revealed that the interaction of condition-by-difficulty degree was significant, F(1, 120) = 5.14, p < 0.05. Furthermore, in the second scenario, which had a lower degree of difficulty, the unpacking manipulation significantly influenced the participants’ time judgment (t(122) = −2.70, p < 0.01), while in the first scenario, the effect was not significant (t(122) = −0.77, p > 0.05). These results supported hypotheses 1a and 1b.
Study 2 tested the time unpacking effect and explored its influence on intertemporal decision making. Hypothesis 2a states that participants in the unpacking condition perceive time delay as longer in the larger but later (LL) option of intertemporal choice, and thus prefer the smaller but sooner (SS) option compared with participants in the packed condition. Hypothesis 2b states that time perception of delay in the LL option mediates the effect of unpacking manipulation on intertemporal choice. The design and procedure were the same as in study 1. A total of 124 participants finished one of two versions of the intertemporal choice computerized questionnaire containing two scenarios. MANOVA analysis found that in both scenarios, people in the unpacking condition perceived a longer time delay (first scenario: F1(1, 98) = 9.03, p1 < 0.01; second scenario: F2(1, 98) = 6.54, p2 < 0.05). They also preferred the SS option in intertemporal decision making, F1(1, 98) = 13.82, p1 < 0.001 and F2(1, 98) = 4.47, p2 < 0.05 in the first and second scenarios, respectively. These results supported hypothesis 2a. Meanwhile, bootstrap mediating analysis supported hypothesis 2b indicating that time perception of delay mediated the influence of unpacking manipulation on intertemporal choice at 90% confidence interval in the first scenario (−0.4660, −0.0220) and 95% confidence interval in the second scenario (−0.4621, −0.0151).
This research identified a new influencing factor in judgment and decision making called the time unpacking effect, and implemented two studies to demonstrate its robustness. Using either an indirect (study 1) or direct (study 2) way to measure time perception substantiated this effect. Our time unpacking effect could be explained by support theory, specifically the attentional explanation. Compared with other influencing factors of time perception, the time unpacking effect is easier to manipulate, therefore it has more practical value in our daily lives.