the most likely explanation of this finding is that the results observed represent a change in neural state associated with attending to a more novel, possibly environmentally relevant noise rather than to any task requirements or salience. These findings are consistent with a previous study that evaluated phase locking of EROs using a complex motor-learning task [105]. In that task, long-range theta phase coherence was stronger in the novel condition compared to learned sequences, independent of task-difficulty. The authors interpreted those findings as a reflection of an increase in the amount of sensory information necessary to integrate novel sequences as compared to learned sequences. Our studies demonstrate that changes in the stimulus characteristics in simple auditory tasks can also produce widespread changes in phase locking over a number of brain areas in the full range of the EEG frequencies (1-50 Hz). It has been suggested that the processing of sensory information, such as those used in our simple auditory task, is primarily guided by automatic “bottom up” processes that do not require as much mental processing [106]. Such effects may be mediated by mesencephalic reticular activation of cortical activity [107].
