Trial-by-Trial Variations in Subjective Attentional State are Reflected in Ongoing Prestimulus EEG Alpha Oscillations

Abstract

Parieto-occipital electroencephalogram (EEG) alpha power and subjective reports of attentional state are both associated with visual attention and awareness, but little is currently known about the relationship between these two measures. Here, we bring together these two literatures to explore the relationship between alpha activity and participants’ introspective judgments of attentional state as each varied from trial-to-trial during performance of a visual detection task. We collected participants’ subjective ratings of perceptual decision confidence and attentional state on continuous scales on each trial of a rapid serial visual presentation detection task while recording EEG. We found that confidence and attentional state ratings were largely uncorrelated with each other, but both were strongly associated with task performance and post-stimulus decision-related EEG activity. Crucially, attentional state ratings were also negatively associated with prestimulus EEG alpha power. Attesting to the robustness of this association, we were able to classify attentional state ratings via prestimulus alpha power on a single-trial basis. Moreover, when we repeated these analyses after smoothing the time series of attentional state ratings and alpha power with increasingly large sliding windows, both the correlations and classification performance improved considerably, with the peaks occurring at a sliding window size of approximately 7 min worth of trials. Our results therefore suggest that slow fluctuations in attentional state in the order of minutes are reflected in spontaneous alpha power. Since these subjective attentional state ratings were associated with objective measures of both behavior and neural activity, we suggest that they provide a simple and effective estimate of task engagement that could prove useful in operational settings that require human operators to maintain a sustained focus of visual attention.

Identifying Granger causal relationships between neural power dynamics and variables of interest

“…(Aue et al, 2009)), we can hope to identify brain activity which reflect this variation. Indeed it has been found that ongoing pre-stimulus alpha power modulates perception performance (see (Jensen and Mazaheri, 2010) for a review), and is negatively correlated with subjective attentional state (Macdonald et al, 2011). Recent studies also demonstrate increased alpha band activity up to 20 resp.…”

The roles of cortical oscillations in sustained attention

“…This approach allows estimation of the contribution of individual frequencies to the analysed signal ( Figure IB). In the case of cognitive electrophysiological research, frequencies are divided into spectral bands with distinct functional associations: delta (1-4 Hz), theta (4-8 Hz), alpha (8)(9)(10)(11)(12)(13)(14), beta (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and gamma (>30 Hz) ( Figure IC).…”

“…It is commonly studied using tasks that require subjects to monitor infrequent and temporally unpredictable signals over extended periods of time (i.e., more than 10 minutes) [7,8]. Changes in sustained attention are measured as both fluctuations [9,10] and deteriorations [7,11] in performance on these tasks. These different measures of performance have been suggested to reflect dissociable cognitive processes [12].…”

EEG indices of reward motivation and target detectability in a rapid visual detection task

“…Practically, neural measures of user state might prove useful in brain-computer interfaces to flag periods of reduced motivation or attentional focus in which missed targets or false alarms would be more likely (Grier, et al, 2003;Mathan et al, 2006a). Indeed, recent evidence has highlighted neural markers that directly correlate with trial-to-trial variations in participants' self-reported attentional state (Macdonald et al, 2011). The present study utilized similar single-trial analysis techniques (Parra et al, 2002) to assess the potential utility of both ERP and oscillatory EEG activity in assessing participants' motivation on single trials.…”

“…Correspondingly, reduced pre-stimulus alpha activity has been shown to be predictive of conscious visual perception in near-threshold detection tasks. For example, decreased alpha activity in the period prior to stimulus onset is associated with improved detection of briefly flashed light stimuli (Ergenoglu et al, 2004), variations in pre-stimulus alpha correlate with subjective ratings of attentional state (Macdonald et al, 2011), and participants with decreased pre-stimulus alpha tend to perform better at detection of backward masked near-threshold stimuli (Hanslmayr et al, 2005). Moreover, phase coupling of pre-stimulus alpha power across scalp electrodes has been shown to be an effective predictor of subsequent correct performance at the level of individual trials with such tasks (Hanslmayr et al, 2007).…”