The effect of phasic alertness on temporal precision.

Many previous studies have found that there is a close relationship between attention and temporal precision. As a mechanism that regulates the intensity of attention, alertness has beneficial influences on perceptual processing. However, little is known regarding whether and how phasic alertness affects temporal precision. Experiment 1 and Experiment 2 used visual and auditory warning cues in a visual temporal order judgment (TOJ) task and a simultaneity judgment (SJ) task to investigate the phasic alerting effect on temporal precision. Participants in the TOJ and SJ tasks were required to make judgments of two successive and synchronous stimuli at various stimulus onset asynchronies (SOAs). Because of dissension regarding the SJ task, Experiment 3 adopted a dual SJ and TOJ task to create a new indicator of participant performance. Although these tasks may differ in the cognitive mechanism they involve, they all produced consistently decreased just noticeable difference (JND) scores and unaltered point of subjective simultaneity (PSS). This suggests that phasic alertness could significantly improve participants' temporal precision (reduced JNDs) of visual perception, without affecting temporal accuracy (unaltered PSS). We then discuss that the alerting effect on temporal sensitivity might be attributed mainly to transient arousal rather than temporal expectancy. Furthermore, the analysis of response ratios at each SOA could distinguish a heightened temporal precision from a reduction of attentional lapses. According to the previous and present studies, phasic alertness might simultaneously benefited the early perceptual processing and late motor execution of responses.