Dimensions of arousal: wakefulness and vigor.

Factors such as shift work, sleep deprivation, and noise affect job performance in part because they affect individuals' levels of arousal. Recent work on arousal has identified two distinct forms of arousal that affect performance in very different ways. Tense arousal represents a continuum from calmness to anxiety, whereas energetic arousal reflects a continuum from tiredness to energy. The three studies reported here sought to determine the usefulness of breaking down energetic arousal still further, into dimensions of wakefulness and vigor. In the first study, a factor analysis of self-reported psychological state data determined that wakefulness and vigor did form separate factors. The second study found that the circadian rhythms of wakefulness and vigor differed; wakefulness increased over the day, whereas vigor peaked at noon. The third study examined the relationship between the two types of arousal and performance on a reading comprehension task. Although both wakefulness and vigor showed an association with performance, only vigor showed the inverted-U-shaped relationship embodied in the Yerkes-Dodson law. These data suggest that distinguishing between wakefulness and vigor will clarify how changes in arousal levels affect productivity. These results also suggest that the schedule for optimal performance of tasks depends on whether they are facilitated by either wakefulness or vigor.