We often fail to see something that at other times is readily detectable. Because the visual stimulus itself is unchanged, this variability in conscious awareness is likely related to changes in the brain. Here we show that the phase of EEG ␣ rhythm measured over posterior brain regions can reliably predict both subsequent visual detection and stimulus-elicited cortical activation levels in a metacontrast masking paradigm. When a visual target presentation coincides with the trough of an ␣ wave, cortical activation is suppressed as early as 100 ms after stimulus onset, and observers are less likely to detect the target. Thus, during one ␣ cycle lasting 100 ms, the human brain goes through a rapid oscillation in excitability, which directly influences the probability that an environmental stimulus will reach conscious awareness. Moreover, ERPs to the appearance of a fixation cross before the target predict its detection, further suggesting that cortical excitability level may mediate target detection. A novel theory of cortical inhibition is proposed in which increased ␣ power represents a "pulsed inhibition" of cortical activity that affects visual awareness.

Alpha oscillations are ubiquitous in the brain, but their role in cortical processing remains a matter of debate. Recently, evidence has begun to accumulate in support of a role for alpha oscillations in attention selection and control. Here we first review evidence that 8–12 Hz oscillations in the brain have a general inhibitory role in cognitive processing, with an emphasis on their role in visual processing. Then, we summarize the evidence in support of our recent proposal that alpha represents a pulsed-inhibition of ongoing neural activity. The phase of the ongoing electroencephalography can influence evoked activity and subsequent processing, and we propose that alpha exerts its inhibitory role through alternating microstates of inhibition and excitation. Finally, we discuss evidence that this pulsed-inhibition can be entrained to rhythmic stimuli in the environment, such that preferential processing occurs for stimuli at predictable moments. The entrainment of preferential phase may provide a mechanism for temporal attention in the brain. This pulsed inhibitory account of alpha has important implications for many common cognitive phenomena, such as the attentional blink, and seems to indicate that our visual experience may at least some times be coming through in waves.

It has been established that successful ignoring of irrelevant distractors depends on the extent to which the current task loads attention. However, the previous load studies have typically employed neutral distractor stimuli (e.g., letters). In the experiments reported here, we examined whether the perception of irrelevant distractor faces would show the same effects. We manipulated attentional load in a relevant task of name search by varying the search set size and found that whereas congruency effects from meaningful nonface distractors were eliminated by higher search load, interference from distractor faces was entirely unaffected by search load. These results support the idea that face processing may be mandatory and generalize the load theory to the processing of meaningful and more complex nonface distractors.

Observers seem surprisingly poor at detecting changes in images following a large transient or flicker. In this study, we compared this change blindness phenomenon between human faces and other common objects (e.g., clothes). We found that changes were detected far more rapidly and accurately in faces than in other objects. This advantage for faces, however, was found only for upright faces in multiple-object arrays, and was completely eliminated when displays showed one photograph only or when the pictures were inverted. These results suggest a special role for faces in competition for visual attention, and provide support for previous claims that human faces are processed differently than stimuli that may be of less biological significance.

Theoretical models in perception assume that confidence is related to the quality or strength of sensory processing. Counter to this intuitive view, here we show that the motor system also contributes to judgments of perceptual confidence. In two experiments we used transcranial magnetic stimulation (TMS) to manipulate response-specific representations in the premotor cortex, selectively disrupting post-decision confidence in visual discrimination judgments. Specifically, stimulation of the motor representation associated with the unchosen response reduced confidence in correct responses, thereby reducing metacognitive capacity without changing visual discrimination performance. Effects of TMS on confidence were observed when stimulation was applied both before and after the discrimination occurred, suggesting confidence depends on late-stage metacognitive processes. These results post constraints on models of perceptual confidence and metacognition by revealing that action-specific information in the premotor cortex contributes to perceptual confidence.

In humans, the primary visual cortex (V1) is essential for conscious vision. However, even without V1 and in the absence of awareness, some preserved ability to accurately respond to visual inputs has been demonstrated, a phenomenon referred to as blindsight. We used transcranial magnetic stimulation (TMS) to deactivate V1, producing transient blindness for visual targets presented in a foveal, TMS-induced scotoma. Despite unawareness of these targets, performance on forced choice discrimination tasks for orientation (experiment 1) and color (experiment 2) were both significantly above chance. In addition to demonstrating that TMS can be successfully used to induce blindsight within a normal population, these results suggest a functioning geniculoextrastriate visual pathway that bypasses V1 and can process orientation and color in the absence of conscious awareness.consciousness ͉ perception ͉ vision ͉ blindsight ͉ transcranial magnetic stimulation

Human superior temporal sulcus (STS) is thought to be a key brain area for multisensory integration. Many neuroimaging studies have reported integration of auditory and visual information in STS but less is known about the role of STS in integrating other sensory modalities. In macaque STS, the superior temporal polysensory area (STP) responds to somatosensory, auditory and visual stimulation. To determine if human STS contains a similar area, we measured brain responses to vibrotactile somatosensory, auditory and visual stimuli using blood-oxygen level dependent functional magnetic resonance imaging (BOLD fMRI). An area in human posterior STS, STSms (multisensory), responded to stimulation in all three modalities. STSms responded during both active and passive presentation of unisensory vibrotactile stimuli and showed larger responses for more intense vs. less intense tactile stimuli, hand vs. foot, and contralateral vs. ipsilateral tactile stimulation. STSms showed responses of similar magnitude for unisensory tactile and auditory stimulation, with an enhanced response to simultaneous auditory-tactile stimulation. We conclude that STSms is important for integrating information from the somatosensory as well as the auditory and visual modalities, and could be the human homolog of macaque STP.

Background. Limited data are available about the effectiveness of early rehabilitation after stroke. Objective. This is the 1st randomized controlled trial of constraint-induced movement therapy (CIMT) in subacute stroke to investigate neurophysiologic mechanisms and long-term outcome. Methods. Within 2 weeks after stroke, 23 patients with upper extremity (UE) weakness were randomized to 2 weeks of CIMT or traditional therapy at an equal frequency of up to 3 h/day. Motor function of the affected UE was blindly assessed before treatment, after treatment, and 3 months after stroke. Transcranial magnetic stimulation (TMS) measured the cortical area evoking movement of the affected hand. Results. Long-term improvement in motor function of the affected UE did not differ significantly between patients who received CIMT versus intensive traditional therapy. All outcome comparisons showed trends favoring CIMT over intensive traditional therapy, but none was statistically significant except for improvements in the Fugl-Meyer (FM) UE motor scale immediately following treatment and in reported quality of hand function at 3 months. Improvement in UE motor function on the FM was associated with a greater number of sites on the affected cerebral hemisphere where responses of the affected hand were evoked by TMS. Conclusions. Future trials of CIMT during early stroke rehabilitation need greater statistical power, more inclusive eligibility criteria, and improved experimental control over treatment intensity. The relationship between changes in motor function and in evoked motor responses suggests that motor recovery during the 1st 3 months after stroke is associated with increased motor excitability of the affected cerebral hemisphere.