Alpha oscillations and stimulus-evoked activity dissociate metacognitive reports of attention, visibility, and confidence in a rapid visual detection task.

Variability in the detection and discrimination of weak visual stimuli has been linked to oscillatory neural activity. In particular, the amplitude of activity in the alpha-band (8-12 Hz) has been shown to impact the objective likelihood of stimulus detection, as well as measures of subjective visibility, attention, and decision confidence. Here we investigate how preparatory alpha in a cued pretarget interval influences performance and phenomenology, by recording simultaneous subjective measures of attention and confidence (experiment 1) or attention and visibility (experiment 2) on a trial-by-trial basis in a visual detection task. Across both experiments, alpha amplitude was negatively and linearly correlated with the intensity of subjective attention. In contrast with this linear relationship, we observed a quadratic relationship between the strength of alpha oscillations and subjective ratings of confidence and visibility. We find that this same quadratic relationship links alpha amplitude with the strength of stimulus-evoked responses. Visibility and confidence judgments also corresponded with the strength of evoked responses, but confidence, uniquely, incorporated information about attentional state. As such, our findings reveal distinct psychological and neural correlates of metacognitive judgments of attentional state, stimulus visibility, and decision confidence when these judgments are preceded by a cued target interval.

Time contracts and temporal precision declines when the mind wanders.

Our perception of time varies considerably from moment to moment, but how this variability relates to endogenous fluctuations in attentional states has been neglected. Here, we tested the hypothesis that perceptual decoupling during spontaneous mind wandering episodes distorts interval timing. In two studies with different visual subsecond interval timing paradigms, participants judged their attentional state on a trial-by-trial basis. Mind wandering states were characterized by underestimation of temporal intervals and a decline in temporal discrimination. Further analyses suggested that temporal contraction during mind wandering, but not the decline in temporal discrimination, could be attributed in part to attentional lapses. By contrast, we did not find any robust evidence that metacognition pertaining to interval timing was altered during mind wandering states. These results highlight the role of transient fluctuations in attentional states in intraindividual variability in time perception and have implications for the perceptual consequences, behavioral markers, and costs and benefits, of mind wandering. (PsycINFO Database Record

Attentional sampling of multiple wagon wheels.

Attending to a periodic motion stimulus can induce illusory reversals of the direction of motion. This continuous wagon wheel illusion (c-WWI) has been taken to reflect discrete sampling of motion information by visual attention. An alternative view is that it is caused by adaptation. Here, we attempt to discriminate between these two interpretations by asking participants to attend to multiple periodic motion stimuli: The discrete attentional sampling account, but not the adaptation account, predicts a decrease of c-WWI temporal-frequency tuning with set size (with a single periodic motion stimulus the c-WWI is tuned to a temporal frequency of 10 Hz). We presented one to four rotating gratings that occasionally reversed direction while participants counted reversals. We considered reversal overestimations as manifestations of the c-WWI and determined the temporal-frequency tuning of the illusion for each set size. Optimal temporal frequency decreased with increasing set size. This outcome favors the discrete attentional sampling interpretation of the c-WWI, with a sampling rate for each individual stimulus dependent on the number of stimuli attended.

Perceptual echoes at 10 Hz in the human brain.

The occipital alpha rhythm (∼10 Hz) is the most prominent electrophysiological activity in the awake human brain, yet its functional role and relation to visual perception are little understood. Transient stimuli normally elicit a short series of positive and negative deflections lasting between 300 and 500 ms: the visual-evoked potential (VEP). Alpha oscillations, on the other hand, are generally suppressed by transient visual input; they only augment in response to periodic ("steady-state") inputs around 10 Hz. Here, we applied reverse-correlation techniques to the visual presentation of random, nonperiodic dynamic stimulation sequences and found that the brain response to each stimulus transient was not merely a short-lived VEP but also included a strong ∼10 Hz oscillation that lasted for more than 1 s. In other words, the alpha rhythm implements an "echo" or reverberation of the input sequence. These echoes are correlated in magnitude and frequency with the observer's occipital alpha rhythm, are enhanced by visual attention, and can be rendered perceptually apparent in the form of ∼10 Hz flicker. These findings suggest a role for the alpha rhythm in the maintenance of sensory representations over time.

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

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.

Visual perceptual load induces inattentional deafness.

In this article, we establish a new phenomenon of "inattentional deafness" and highlight the level of load on visual attention as a critical determinant of this phenomenon. In three experiments, we modified an inattentional blindness paradigm to assess inattentional deafness. Participants made either a low- or high-load visual discrimination concerning a cross shape (respectively, a discrimination of line color or of line length with a subtle length difference). A brief pure tone was presented simultaneously with the visual task display on a final trial. Failures to notice the presence of this tone (i.e., inattentional deafness) reached a rate of 79% in the high-visual-load condition, significantly more than in the low-load condition. These findings establish the phenomenon of inattentional deafness under visual load, thereby extending the load theory of attention (e.g., Lavie, Journal of Experimental Psychology. Human Perception and Performance, 25, 596-616, 1995) to address the cross-modal effects of visual perceptual load.

Load induced blindness.

Although the perceptual load theory of attention has stimulated a great deal of research, evidence for the role of perceptual load in determining perception has typically relied on indirect measures that infer perception from distractor effects on reaction times or neural activity (see N. Lavie, 2005, for a review). Here we varied the level of perceptual load in a letter-search task and assessed its effect on the conscious perception of a search-irrelevant shape stimulus appearing in the periphery, using a direct measure of awareness (present/absent reports). Detection sensitivity (d') was consistently reduced with high, compared to low, perceptual load but was unaffected by the level of working memory load. Because alternative accounts in terms of expectation, memory, response bias, and goal-neglect due to the more strenuous high load task were ruled out, these experiments clearly demonstrate that high perceptual load determines conscious perception, impairing the ability to merely detect the presence of a stimulus--a phenomenon of load induced blindness.