Tracking wakefulness as it fades: micro-measures of Alertness

Abstract

16A major problem in psychology and physiology experiments is drowsiness: around a third of 17 participants show decreased wakefulness despite being instructed to stay alert. In some non-18 visual experiments participants keep their eyes closed throughout the task, thus promoting the 19 occurrence of such periods of varying alertness. These wakefulness changes contribute to 20 systematic noise in data and measures of interest. To account for this omnipresent problem in 21 data acquisition we defined criteria and code to allow researchers to detect and control for 22 varying alertness in electroencephalography (EEG) experiments. We first revise a visual-scoring 23 method developed for detection and characterization of the sleep-onset process, and adapt the 24 same for detection of alertness levels. Furthermore, we show the major issues preventing the 25 practical use of this method, and overcome these issues by developing an automated method 26 based on frequency and sleep graphoelements, which is capable of detecting micro variations in 27 alertness. The validity of the automated method was verified by training and testing the algorithm 28 using a dataset where participants are known to fall asleep. In addition, we tested generalizability 29 by independent validation on another dataset. The methods developed constitute a unique tool 30 to assess micro variations in levels of alertness and control trial-by-trial retrospectively or 31 prospectively in every experiment performed with EEG in cognitive neuroscience. 32

Wandering minds, sleepy brains: lapses of attention and local sleep in wakefulness

“…However, alpha oscillations are not an unambiguous marker of sleepiness, as they only transiently increase with sleepiness. Alpha power is low when participants are both fully alert or, on the contrary, approaching sleep onset 51,52 . Thus, the divergent results obtained regarding mind wandering and alpha oscillations could be explained by a shift in participants' baseline level of fatigue.…”

Decreasing alertness modulates perceptual decision-making

“…In the drowsy session, the subjects were allowed to fall asleep and hence some trials would be considered as alert and some would be drowsy. For each trial in the drowsy session, pre-trial epochs were analysed using the micro-measures algorithm (Jagannathan et al, 2018) . Each trial was classed as 'alert', 'drowsy(mild)' , 'drowsy(severe)'.…”

“…While measures using alpha-theta assume participants being equally alert and drowsy (not always true) and manual Hori scoring suffers from subjectivity dependent on the experience of the human scorer. Recently we published a novel computational method to track alertness levels using electroencephalography (EEG) that shows robust outcomes (Jagannathan et al, 2018) , and has been successfully applied in other studies to explore the effect of alertness on executive control systems (Canales-Johnson et al) . Here we decided to take advantage of this technique and use an experiment (auditory spatial localisation task) with a known behavioural asymmetry (Bareham et al, 2014) to investigate how decision-making is modulated by fluctuations in tonic alertness.…”

Decreased alertness reconfigures cognitive control networks

“…The pre-trial period (-1500 to 0ms) before each tone was used in classifying the corresponding trial as awake or drowsy. Pre-trial epochs were analysed using the micro-measures algorithm (Jagannathan et al, 2018) and each trial was classified as 'alert', 'drowsy (mild)' or 'drowsy (severe)'.…”

“…In EEG recordings, conflict-related processes are often measured by quantifying the power of theta-band neural oscillations (4-8 Hz) (Luu et al, 2004;Trujillo and Allen, 2007;Cohen et al, 2008;Cavanagh et al, 2010;Nigbur et al, 2012;Cohen and van Gaal, 2014). In combination with a recently validated method to automatically detect drowsiness periods from EEG (Jagannathan et al, 2018) we here use conflictive information to map behavioural and neural markers of cognitive control as they get modulated by ongoing fluctuations in arousal.…”