Effects of intensity and order of stimuli presentation on AEPs: an analysis of the consistency of EP augmenting/reducing in the auditory modality

Objectives: (1) To achieve a better understanding of the intensity dependence function of AEPs recorded at fronto-central and temporal electrode sites; (2) To assess the possible influence of the order of stimuli presentation on this function; and (3) To investigate if a subjectʹs AEPs augmenting or reducing (A/R) tendency is consistent throughout two intra-session runs. Methods: Two sequences of 288 stimuli of different intensities (60, 80, 90 and 110 dB SPL) were delivered to 29 psychology students. In the first run, stimuli were presented in 4 consecutive blocks of 72 tones of each intensity, either in an ascendant (from lowest to loudest stimuli) or descendent (from loudest to lowest) way. In the second run, a pseudo-randomized sequence of stimuli of the 4 intensities was presented. Results: (1) AEPs recorded at fronto-central electrodes showed a stronger intensity dependence than those recorded at temporal leads; (2) The delivery of tones of different intensities in an aleatory sequence provoked higher amplitudes at Fz and Cz – especially for the loudest tones – but not at temporal leads; (3) The individualʹs AEP responses to stimuli of increasing intensity are highly consistent throughout two intra-session runs. Conclusions: The different findings obtained for the fronto-central N1P2 and the T complex in relation to the effect of intensity and order of stimuli presentation may be explained in terms of the cortical origin of those components. The higher amplitudes found with an aleatory sequence, especially for the highest intensity stimuli, may reflect that these stimuli capture the subjectʹs attention and provoke an enhancement of the N1 component. The implications of the present results for investigation into A/R and the clinical relevance of this phenomenon are discussed.