Duration refers to the time that events last. If we think of tempo as the speed of events, then duration is the speed of the clock itself. For the physicist, the duration of a “second” is precise and unambiguous: it is equal to 9,192,631,770 cycles of the frequency associated with the transition between two energy levels of the isotope cesium-133. In the realm of psychological experience, however, quantifying units of time is a considerably clumsier operation. When people are removed from the cues of “real” time ─ be it the sun, bodily fatigue, or timepieces themselves ─ it doesn’t take long before their time sense breaks down. And it is this usually _____(A)_____ psychological clock, as opposed to the time on one’s watch, that creates the perception of duration that people experience.

Theoretically, a person who mentally stretches the duration of time should experience a slower tempo. Imagine, for example, that baseballs are pitched to two different batters. The balls are thrown every 5 seconds for 50 seconds, so a total of 10 balls are thrown. We now ask both batters how much time has passed. Let’s say that batter number one (who loves hitting) feels the duration to be 40 seconds. Batter number two (bored by baseball) believes it to be 60 seconds. Psychologically, then, the first person has experienced baseballs approaching every four seconds while the second sees it as every six seconds. The perceived tempo, in other words, is _____(B)_____ for batter number one.

* isotope: 동위원소 ** clumsy: 서투른