We examined relationships between the phase of narrow-band electroencephalographic (EEG) activity at stimulus onset and the resultant event-related potentials (ERPs) in an equiprobable auditory Go/NoGo task with a fixed SOA, in the context of a novel conceptualisation of orthogonal phase effects (cortical negativity vs. positivity, negative driving vs. positive driving, waxing vs. waning). ERP responses to each stimulus type were analysed. Prestimulus narrow-band EEG activity (in 1Hz bands from 1 to 13Hz) at Cz was assessed for each trial using FFT decomposition of the EEG data. For each frequency, the cycle at stimulus onset was used to sort trials into four phases, for which ERPs were derived from the raw EEG activity at 9 central sites. The occurrence of preferred phase-defined brain states was confirmed at a number of frequencies, crossing the traditional frequency bands. As expected, these did not differ between Go and NoGo stimuli. These preferred states were associated with more efficient processing of the stimulus, as reflected in differences in latency and amplitude of the N1 and P3 ERP components. The present results, although derived in a different paradigm by EEG decomposition methods different from those used previously, confirm the existence of preferred brain states and their impact on the efficiency of brain dynamics involved in perceptual and cognitive processing.