Awareness is related to reduced post-stimulus alpha power: a no-report inattentional blindness study

Delineating the neural correlates of sensory awareness is a key requirement for developing a neuroscientific understanding of consciousness. A neural signal that has been proposed as a key neural correlate of awareness is amplitude reduction of 8-14 Hz alpha oscillations. Alpha oscillations are also closely linked to processes of spatial attention, providing potential alternative explanations for past results associating alpha oscillations with awareness. We employed a no-report inattentional blindness (IB) paradigm with electroencephalography to examine the association between awareness and the power of 8-14 Hz alpha oscillations. We\ua0asked whether the alpha-power decrease commonly reported when stimuli are\ua0perceived is related to\ua0awareness, or other factors that commonly\ua0confound awareness investigations, specifically task-relevance and visual salience. Two groups of\ua0participants performed a target\ua0discrimination task at fixation\ua0while irrelevant non-salient shape probes were presented briefly in the left or\ua0right visual field. One group was explicitly informed of\ua0the\ua0peripheral probes at the commencement of the experiment (the control group),\ua0whereas the other was not told about the probes until halfway through the experiment (IB\ua0group). Consequently, the IB group remained unaware of the probes\ua0for the first half of the experiment. In all conditions in which participants\ua0were aware of the probes, there was an\ua0enhanced negativity in the event-related potential (the\ua0visual awareness negativity). Furthermore, there was an extended\ua0contralateral alpha-power decrease when the probes were\ua0perceived,\ua0which was not present when they failed to reach awareness. These results suggest alpha oscillations are intrinsically associated with awareness\ua0itself. This article is protected by copyright. All rights reserved

Preparatory Encoding of the Fine Scale of Human Spatial Attention

Our attentional focus is constantly shifting: In one moment, our attention may be intently concentrated on a specific spot, whereas in another moment we might spread our attention more broadly. Although much is known about the mechanisms by which we shift our visual attention from place to place, relatively little is known about how we shift the aperture of attention from more narrowly to more broadly focused. Here we introduce a novel attentional distribution task to examine the neural mechanisms underlying this process. In this task, participants are presented with an informative cue that indicates the location of an upcoming target. This cue can be perfectly predictive of the exact target location, or it can indicate-with varying degrees of certainty-approximately where the target might appear. This cue is followed by a preparatory period in which there is nothing on the screen except a central fixation cross. Using scalp EEG, we examined neural activity during this preparatory period. We find that, with decreasing certainty regarding the precise location of the impending target, participant RTs increased whereas target identification accuracy decreased. Additionally, the multivariate pattern of preparatory period visual cortical alpha (8-12 Hz) activity encoded attentional distribution. This alpha encoding was predictive of behavioral accuracy and RT nearly 1 sec later. These results offer insight into the neural mechanisms underlying how we use information to guide our attentional distribution and how that influences behavior

Preparatory Encoding of the Fine Scale of Human Spatial Attention

Our attentional focus is constantly shifting: In one moment, our attention may be intently concentrated on a specific spot, whereas in another moment we might spread our attention more broadly. Although much is known about the mechanisms by which we shift our visual attention from place to place, relatively little is known about how we shift the aperture of attention from more narrowly to more broadly focused. Here we introduce a novel attentional distribution task to examine the neural mechanisms underlying this process. In this task, participants are presented with an informative cue that indicates the location of an upcoming target. This cue can be perfectly predictive of the exact target location, or it can indicate-with varying degrees of certainty-approximately where the target might appear. This cue is followed by a preparatory period in which there is nothing on the screen except a central fixation cross. Using scalp EEG, we examined neural activity during this preparatory period. We find that, with decreasing certainty regarding the precise location of the impending target, participant RTs increased whereas target identification accuracy decreased. Additionally, the multivariate pattern of preparatory period visual cortical alpha (8-12 Hz) activity encoded attentional distribution. This alpha encoding was predictive of behavioral accuracy and RT nearly 1 sec later. These results offer insight into the neural mechanisms underlying how we use information to guide our attentional distribution and how that influences behavior