Attentional selection mechanisms in visual cortex involve changes in oscillatory activity in the EEG alpha band (8 to 12 Hz) – decreased alpha indicating focal cortical enhancement and increased alpha indicating suppression. This has been observed for spatial selective attention and attention to stimulus features such as color and motion. Theoretical work suggests that the control of oscillatory neural activity may be a crucial component of the mechanisms of attentional signal propagation through cortex, and in particular, the modulation of alpha band activity might constitute an information routing mechanism across all of visual cortex. This hypothesis leads to the prediction that alpha band modulation should also accompany attention to high-level visual features, such as object categories. To test this prediction, we investigated whether attention to objects involves alpha-mediated changes in focal cortical excitability. We conducted three experiments to look for systematic differences in the pattern of EEG alpha power across the scalp, and assess whether any such systematic differences were driven by the engagement of object-based attention to different object categories. In Experiment 1, twenty volunteers (8 males; 12 females) were cued (80% predictive) on a trial-by-trial basis to different objects (faces, scenes, or tools).¬ Support vector machine decoding of alpha power patterns revealed that late (>500 msec latency) in the cue-to-target foreperiod, only EEG alpha differed with the to-be-attended object category. In Experiment 2, to eliminate the possibility that decoding of physical features of the cues led to our results, twenty-five participants (9 males; 16 females) performed a similar task where cues were non-predictive of the object category. Alpha decoding was now only significant in the early (<200 msec) foreperiod. In Experiment 3, to eliminate the possibility that task set differences between the different object categories led to our Experiment 1 results, twenty participants (9 males; 11 females) performed a predictive cuing task where the discrimination task for different objects was identical across object categories. The results replicated Experiment 1. Together, these findings support the hypothesis that the neural mechanisms of visual selective attention involve focal cortical changes in alpha power for not only simple spatial and feature attention, but also high-level object attention in humans. These findings support the Specificity of Control model of attention, according to which a top-down source of attentional control signals issues instructions over individualized channels to sensory sites according to the particular receptive properties of those sites, and an identical mechanism to elaborate information processing operates at the sensory sites. We followed up the planned analyses with a series of ERP decoding analyses to corroborate our theoretical interpretation, and to provide evidence that alpha band modulation is directly related to an immediate perceptual benefit afforded by attention. Altogether, our findings suggest that the modulation of oscillatory neural activity in the alpha frequency band is an essential component of the enhancement mechanism of attention, operating throughout visual cortex.

Attention is the ability to concentrate on relevant events and objects while ignoring distractions. In laboratory settings, studies of top-down voluntary attention often employ paradigms with predictive or instructional cues to direct participants’ attention. However this is not how attention always operates in the real world, as voluntary attention can be guided volitionally, without external cues. The volitional control of attention without external influence is termed “willed attention”. This concept shares terminology with the study of willed motor actions, where motor actions are self-initiated. In line with the research on willed action, willed attention involves participants freely choosing where to direct their focus without external guidance. Here, I present three electrophysiological studies which center on the moment-to-moment neural activity which influences these willful shifts of attention. By studying the EEG signals obtained from humans, I have assessed the transient brain electrical patterns underlying shifts of willed attention in three separate human EEG experiments. First, I review the field of willed attention and relate it to the longstanding work on willed action and free will. Then, I present a study that breaks out of the usual cue-to-target paradigm and has no temporal constraints, allowing participants to shift attention when and where they would like to. Following that, an experiment focused on overt willed attention (with concomitant eye movements) is presented, where participants are given a visual search task with no external guidance, then I assess the electrophysiology preceding the first saccade into the visual search array. The third and final experiment presented here is a study of willed attention to color, where instead of space being the domain of interest, participants are allowed to choose to attend to one of two colors. In this dissertation, I expand the field of willed attention conceptually by relating the prior research conducted to research in surrounding fields, and experimentally by presenting experiments with different constraints and in different domains of vision than previously studied.