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 dependen ce 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 subject's 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 intensi ty, either in an ascendant (from lowest to loudest stimuli) or descendent ( from loudest to lowest) way. In the second run, a pseudo-randomized sequenc e of stimuli of the 1 intensities was presented. Results: (1) AEPs recorded at fronto-central electrodes showed a stronger i ntensity 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 Ct - especially for the loudest tones - but not at tem poral leads; (3) The individual's AEP responses to stimuli of increasing in tensity are highly consistent throughout two intra-session runs. Conclusions: The different findings obtained for the fronto-central N1P2 an d 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 com ponents. The higher amplitudes found with an aleatory sequence, especially for the highest intensity stimuli, may reflect that these stimuli capture t he subject's attention and provoke an enhancement of the N1 component. The implications of the present results for investigation into A/R and the clin ical relevance of this phenomenon are discussed. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.