Abstract
Alpha oscillations (8–14 Hz) are the dominant rhythm in the awake brain, which is proposed to set the internal state of the neural system. Previous work has demonstrated that states of decreased spontaneous alpha oscillatory power correlate with enhanced neural excitability. However, whether and how changes in neural excitability influence sensory processing and manifest in behavior are yet open questions. To address these questions, we used a novel paradigm to experimentally manipulate human participants’ decision criterion (i.e., how certain percepts are used for decision) in a visual detection task. In different blocks, we primed participants differently with clearly visible stimuli to introduce either a liberal or conservative decision criterion for the subsequently presented ambiguous stimuli. While we observed prevalent criterion shifts in participants’ decisions under different priming conditions, the pre-stimulus oscillatory power or phase were not modulated by different priming conditions. Trial-by-trial analyses showed that lower spontaneous alpha oscillatory power in visual areas encoding the target stimuli leads to higher accuracy in performing the task, which is accompanied with enhanced information content decodable in the neural activity patterns. Moreover, spontaneous alpha oscillatory phase in anterior frontal and superior parietal regions modulate accuracy in a phasic sinusoidal manner. Together, our results indicate that as neural excitability increases in the state of decreased occipital alpha-band oscillatory power, the sensory representation of task-relevant visual stimuli is sharpened and consequently leads to improved behavioral discriminability.
