Visual attention, reaction time, and self-reported alertness upon awakening from sleep bouts of varying lengths

The aim of the present study was to examine visual attention, especially the executive control functions that deal with conflict, when participants were in a low arousal state shortly after a nighttime awakening. Fifteen participants spent four consecutive nights at a laboratory and performed a flankers task using two levels of target-distractor spacing (0.75° and 1.50°) and three trial types (compatible, incompatible, and neutral). The first night was a habituation night. For the next three nights, participants went to sleep at 2300 hours and were then awakened at either 2400 hours (1-h sleep bout), 0300 hours (4-h sleep bout), or 0600 hours (7-h sleep bout) and were administered a flankers task and a self-report questionnaire that measured arousal level. These testing times were counter-balanced across participants, and a 2100 hours (pre-sleep) flankers task was also randomly assigned to be completed on one of the testing nights. Response time on neutral-flanker trials was increased if participants were awakened from a sleep bout and was slowest at 0300 hours, appearing to parallel circadian body temperature. In contrast, failures of selective attention, as indexed by the difference between compatible and incompatible trials, increased linearly as a function of the length of the sleep bout. Compared to the 2100 hours pre-sleep condition, self-reported energy was lower and Tiredness was higher after awakening from a sleep bout. Taken together, the current data suggest a dissociation between the processes that perform a non-conflict task and the executive control of attention. Specifically, longer sleep bouts seem to be associated with greater difficulty in inhibiting task-irrelevant information, perhaps due to a sleep inertia effect affecting the anterior cingulate cortex.