Selective attention in young women awakened from nocturnal sleep

Background: Selective attention, the ability to focus on relevant stimuli for information processing while ignoring irrelevant stimuli, is pertinent to many human activities. However, there have been few attempts to measure circadian influences on selective attention. Methods: As part of a larger protocol, 14 female subjects spent 3 nights at a General Clinical Research Center. On a given night, subjects were awakened at either 24:00, 03:00, or 06:00 hours and administered a computerized flankers task using two levels of spacing for the flankers ("near," 0.75°; and "far," 1.5°) and three types of flanker trials (compatible, incompatible, and neutral). Before sleeping on the first or second night, subjects were also administered the flankers task at 21:00. Results: Neutral flanker trials resulted in faster reaction times (RTs) at 21:00 than the three nighttime conditions. The flanker effect (i.e., the difference between compatible and incompatible trials) was also significantly smaller in the 21:00 condition, but did not differ among the other three conditions. An effect component analysis indicated significantly more interference than facilitation. For incompatible/far trials, there was a trend toward a slowing down of RT across the four time conditions. Conclusion: The present study demonstrated that the flankers task, which measures selective attention, may be a relevant measure of performance in circadian studies. The analyses suggest increases in RT if subjects are awakened from a bout of sleep, and if these results are confirmed, failures of selective attention mechanisms to inhibit stimuli that require a competing response when subjects are awakened from sleep.