Effects of attention and background verbal stimuli on event-related potentials to tone pips in humans

The effects of attention and background verbal stimuli on event-related potentials (ERPs) following tone pips were assessed under four conditions: tone pips presented alone when attending and ignoring the tones and tone pips plus verbal stimuli when attending the tones and attending the verbal stimuli. The data were quantified in terms of the N1-P2 amplitude and the similarity (correlation) between ERPs in corresponding placements over the two hemispheres. The main results were that attention influenced the ERP amplitude only with the verbal stimuli, that interhemispheric similarity was greatest with the tones only, and that similarity was greater under the tone plus verbal stimuli condition during tone-attention instructions.